Curious: How many stars can we 'see' in our own galaxy?
B.T.World
With the naked eye, I think we can see several thousand.
With good amateur telescopes, I assume maybe hundreds
of thousands or maybe even millions.
With space telescopes such as Hubble, I assume we could see billions.
With our galaxy's size roughly being 100,000 light years in diameter,
what % of the 100-200 billion stars can't we 'see'?
E.g. blocked by the black hole at the center or blocked by billions
of other stars or blocked by gigantic gas clouds?
Where are the stars we can't see? At the other side of the
black hole or is it all the stars beyond e.g. 10000 light years,
as their light is blocked or masked by the in-between stars?
As you can tell, I don't know the basics about astronomy so
any explanation or good URL is appreciated!
mitch.nico...@gmail.com
I heard two other numbers: 400 billion and even a trillion.
ah
> With 100 - 200 billion stars in our Milky Way, how many can we see?
> With the naked eye, I think we can see several thousand.
49,357 by my last count.
>
> With good amateur telescopes, I assume maybe hundreds
> of thousands or maybe even millions.
>
> With space telescopes such as Hubble, I assume we could see billions.
>
> With our galaxy's size roughly being 100,000 light years in diameter,
> what % of the 100-200 billion stars can't we 'see'?
>
> E.g. blocked by the black hole at the center or blocked by billions
> of other stars or blocked by gigantic gas clouds?
Opaque mass.
btw, the 'hole' at the center is actually purple.
>
> Where are the stars we can't see? At the other side of the
> black hole or is it all the stars beyond e.g. 10000 light years,
> as their light is blocked or masked by the in-between stars?
Opacity is a function of the sum of the quantity and type the mass in-between.
>
> As you can tell, I don't know the basics about astronomy so
> any explanation or good URL is appreciated!
Sam Wormley
> With 100 - 200 billion stars in our Milky Way, how many can we see?
> With the naked eye, I think we can see several thousand.
>
> With good amateur telescopes, I assume maybe hundreds
> of thousands or maybe even millions.
>
> With space telescopes such as Hubble, I assume we could see billions.
>
IIRC the 11 CD-ROM USNO stellar database has about half a billion
stars cataloged. Estimates for the mass of the Milky Way range
from 140 to 700 billion solar masses.
That's a lot of stars.
B.T.World
I researched ah's 'opacity' but a rough answer to my question is
still difficult to find. Maybe the question cannot easily be
answered.
Does half a billion stars 'cataloged' imply we can only see or
'catalog' say 0.5 to 2 billion, which would be less than 1% of
the stars in the Milky Way?
BradGuth
Perhaps we've cataloged all of 0.1%, thus guessing at the other 99.9%,
if we're even that good.
. - Brad Guth
B.T.World
I am beginning to think that we cannot 'see' a large % of the stars in
our
own galaxy from any viewpoint in our solar system (which is only a
small
speck and at 25,000 light years from the galactic center).
I also realize that using simple extrapolation from the number of
stars we
can see and count in the more nearby regions of our galaxy, we can
make
an estimate of the total number of stars in our spiral-shaped galaxy
based
on that distribution. The estimate now is 100-200 billion. Of course
it can
be anywhere from 50 billion to 500 billion.
My question is really what % of the stars can we see or can't we see
from any viewpoint in the solar system. Does somebody know a study/
URL that covers this question?
Thanks,
B.T.
BradGuth
If there were such a study/URL group of sufficient expertise, they're
either too afraid to share or simply not permitted to share whatever
they know.
For all we know, our Milky Way could host nearly a full trillion
stars, especially if the full spectrum of such stars are taken into
account, with our visual accounting of perhaps as few as .0001%, and
best instrument accounting of not more than .01%
. - Brad Guth
B.T.World
Why would they be afraid to share or simply not be permitted to share
whatever
they know? Most scientists like to share and it also has no military
or business
value (yet :-)).
Also are you saying that only .0001 - .01% of the estimated number of
stars is
'visible', or do you mean that our efforts to 'see' and/or catalog
them has
up to now been limited to below .01%. I understand what you are saying
that
the total number of stars in own galaxy may be much larger than the
100-200 billion figure and that it is therefore difficult to make a
good guess at
the percentage that can be 'seen'.
I was looking for a ballpark idea of how many of the stars in our
galaxy we can
really 'see' and to know that it may be far below 1% is a good enough
answer.
B.T.
BradGuth
You obviously do not appreciate the faith-based power and glory of
their DARPA organization, that which doesn't take kindly to hearing
the truth about much of anything unless it makes all of their kind
look every bit as good or better than God.
>
> Also are you saying that only .0001 - .01% of the estimated number of
> stars is
> 'visible', or do you mean that our efforts to 'see' and/or catalog
> them has
> up to now been limited to below .01%. I understand what you are saying
> that
> the total number of stars in own galaxy may be much larger than the
> 100-200 billion figure and that it is therefore difficult to make a
> good guess at
> the percentage that can be 'seen'.
The human visual spectrum is at best extremely piss poor at seeing
much of anything that's out there. Without technology we can't see
into the IR or UV spectrums, and there's certainly more than IR and UV
to behold. The human visual sensitivity is good at seeing green,
otherwise poor at seeing deep red or violet.
The physically sooty and artificial light polluted atmosphere of Earth
does a darn good job of further filtering and nearly blocking out as
well as distorting much of what we humans and unfiltered Kodak film
could otherwise clearly detect from our physically dark moon.
>
> I was looking for a ballpark idea of how many of the stars in our
> galaxy we can
> really 'see' and to know that it may be far below 1% is a good enough
> answer.
> B.T.
I think at best of our limited human visual perception, along with the
best optics of KECK, isn't worth 0.0001% of items larger than Earth
(Sirius-B for example is barely visible to the human eye if knowing
exactly where to look, and only if there's a sufficient degree of
custom filtered optics utilized).
Double that distance to Sirius and you can pretty much forget about
ever seeing Sirius-B without having to involve highly specialized
instruments.
Perhaps with those extended spectrum CCD instruments of IR and UV
included is where team KECK might stand a remote chance of detecting
1% of whatever's Earth+ significant within our Milky Way, although off-
world instruments are what's really required.
. - Brad Guth
John C. Polasek
<btrw...@yahoo.com> wrote:
>With 100 - 200 billion stars in our Milky Way, how many can we see?
>With the naked eye, I think we can see several thousand.
>
>With good amateur telescopes, I assume maybe hundreds
>of thousands or maybe even millions.
>
>With space telescopes such as Hubble, I assume we could see billions.
>
>With our galaxy's size roughly being 100,000 light years in diameter,
>what % of the 100-200 billion stars can't we 'see'?
>
>E.g. blocked by the black hole at the center or blocked by billions
>of other stars or blocked by gigantic gas clouds?
>
>Where are the stars we can't see?
All stars younger than our Sun are invisible. Science is calling this
dark matter. But they have the wrong geometry. I am preparing a paper
to show this. But I dont think that 's what you meant.
>At the other side of the
>black hole or is it all the stars beyond e.g. 10000 light years,
>as their light is blocked or masked by the in-between stars?
>
>As you can tell, I don't know the basics about astronomy so
>any explanation or good URL is appreciated!
>
John Polasek
Sam Wormley
> All stars younger than our Sun are invisible. Science is calling this
> dark matter. But they have the wrong geometry. I am preparing a paper
> to show this. But I dont think that 's what you meant.
There are many stars recently born in stellar birthing regions
of our galaxy... big suckers that live for just a few million
years... obviously younger than our sun that we measure the
luminosity and spectra of. Visible, yes!
John C. Polasek
wrote:
Many, but not enough. These are not main sequence stars. They are
accidental products of already existent older stars.
I am talking about the 95% that are "dark matter", in number about
10^22.
Greg Neill
news:406u149dsvis75dp3...@4ax.com
There's no evidence (yet) for dark matter stars, or that dark
matter clumps into stellar-sized objects.
Sam Wormley
Yes they are main sequence stars formed from collapsing gas and
dust clouds... The edidence is clearly visible over a broad range
of wave lengths.
Stars are made of baryonicv matter.
Dark matter is tenuous enough that is clumps only on extragalactic
scales... Dark Matter gravitation is measured by the motions in and
of galaxies and gravitational lensing.
John C. Polasek
wrote:
>John C. Polasek wrote:
>> On Mon, 05 May 2008 02:37:59 GMT, Sam Wormley <swor...@mchsi.com>
>> wrote:
>>> There are many stars recently born in stellar birthing regions
>>> of our galaxy... big suckers that live for just a few million
>>> years... obviously younger than our sun that we measure the
>>> luminosity and spectra of. Visible, yes!
>>>
>> Many, but not enough. These are not main sequence stars. They are
>> accidental products of already existent older stars.
>> I am talking about the 95% that are "dark matter", in number about
>> 10^22.
>
> Yes they are main sequence stars formed from collapsing gas and
> dust clouds... The edidence is clearly visible over a broad range
> of wave lengths.
Then I used the wrong terminology 'main sequence'.
I meant their lineage and origin does not follow that of our familiar
ancient stars, but they are, as you seem to agree, accidental products
of "collapsing gas and dust" (oh, my!) of contemporary ancient stars.
> Stars are made of baryonicv matter.
>
> Dark matter is tenuous enough that is clumps only on extragalactic
> scales... Dark Matter gravitation is measured by the motions in and
> of galaxies and gravitational lensing.
Your two declarative sentences lead me to believe that you endorse
these searches for WIMPs, MACHO's and neutralino's, all presently
undefined, yet adequately funded. Do you?
I will show that these exotic (not to say, quixotic) particles need
not exist; quite ordinary phenomena are the cause.
John Polasek
>
>
Greg Neill
> wrote:
>> Yes they are main sequence stars formed from collapsing gas and
>> dust clouds... The edidence is clearly visible over a broad range
>> of wave lengths.
> Then I used the wrong terminology 'main sequence'.
>
> I meant their lineage and origin does not follow that of our familiar
> ancient stars, but they are, as you seem to agree, accidental products
> of "collapsing gas and dust" (oh, my!) of contemporary ancient stars.
>> Stars are made of baryonicv matter.
There's still quite a bit of primodial hydrogen and
helium hanging around in the galaxy that can form
new stars without too much in the way of "metal"
contamination from previous generations.
Steve Willner
In article <a1bae604-910a-47b6...@z24g2000prf.googlegroups.com>,
"B.T.World" <btrw...@yahoo.com> writes:
> With 100 - 200 billion stars in our Milky Way, how many can we see?
> With the naked eye, I think we can see several thousand.
Good estimate. Probably around 6500 counting both hemispheres, all
times of year, and assuming good eyesight and dark skies. The exact
number depends on what "good eyesight" means; some people with
extraordinary eyesight could probably see more.
> With good amateur telescopes, I assume maybe hundreds
> of thousands or maybe even millions.
"Good amateur telescopes" have gotten a lot better in the last few
years. Also, it depends on whether you mean "with the naked eye" or
if you allow photography or (even better) long exposures with CCD
cameras. It would take some actual work to make a real estimate, but
even for strictly visual observing through a 10-inch or so telescope,
it looks as though there would be tens of millions of stars visible.
(At the Galactic poles, there are about 100 stars per square degree
brighter than mag 14.)
> With space telescopes such as Hubble, I assume we could see
> billions.
There are at least three problems than limit the number of Milky Way
stars we can see. In all cases, it would take some work to do a real
calculation, but I think in principle it could be done. Numbers
below are my best guesses without calculating anything, but I may be
grossly wrong.
1. Some stars are simply too faint and far away. Typical exposures
with Hubble might reach magnitude 25. With this sensitivity, and if
nothing else mattered, the Sun would be easily visible on the far
edge of the Galaxy. The longest Hubble exposures, such as the famous
Hubble Deep Field, can go quite a bit fainter than this. Most stars,
however, are fainter than the Sun. The faintest of all are something
like 10000 times fainter. I'm guessing well under 10% of all Milky
Way stars are bright enough to be seen in typical Hubble exposures.
2. The Milky Way contains vast quantities of dust -- small solid
particles. You can easily see foreground dust clouds in wide-field
images of the Milky Way or with your naked eye if you look on a dark
night. Because both stars and dust are concentrated to the Galactic
plane, the dust probably blocks more than 90% of the stars that would
otherwise be visible.
3. When two or more stars are close together on the sky, observations
may not be able to "resolve" or separate them. The obvious example
of this is the Milky Way itself, which looks like a solid band of
light to the naked eye but is really made up of the summed light of
many stars. (The generic term for inability to resolve multiple
sources is "confusion.") With a good telescope, or even binoculars,
you can begin to see the Milky Way stars separately. In principle, a
sufficiently large telescope above Earth's atmosphere could resolve
each Milky Way star, but Hubble and other existing telescopes cannot
do so. Many of the stars lost to confusion are the same ones lost
because of dust extinction, but probably another factor of 3 to 5 are
lost as well.
Thus my *guess* is that if we could map the entire sky with Hubble
(which would take what, thousands of years of observing time?), we
could detect something like 1% of the Milky Way stars. As I caution
above, this is a guess and may be wildly wrong. Anybody care to do a
real calculation?
Existing star catalogs, as someone mentioned, contain a much smaller
fraction than this.
> E.g. blocked by the black hole at the center
The black hole is tiny in comparison with the size of the galaxy. I
doubt it blocks even a single star.
--
Steve Willner Phone 617-495-7123 swil...@cfa.harvard.edu
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)
John C. Polasek
These clouds have the makings of a cleancut, landmark test to finally
validate general relativity. GR should define and quantify the exact
cause for an implosion of this gaseous detrita, vigorous enough to
register on our cameras, and to, at least, solder the particles
together, if not to glow for a long time. (and twinkle).
I don't rule it out, but it still fails the numbers criterion: circa
10^22.
John Polasek
BradGuth
> On Mon, 5 May 2008 14:55:39 -0400, "Greg Neill"
>
>
>
> >"John C. Polasek" <jpola...@cfl.rr.com> wrote in message
> >news:32lu14dpbunnkh3iu...@4ax.com
> >> On Mon, 05 May 2008 16:59:55 GMT, Sam Wormley <sworml...@mchsi.com>
> >> wrote:
>
> >>> Yes they are main sequence stars formed from collapsing gas and
> >>> dust clouds... The edidence is clearly visible over a broad range
> >>> of wave lengths.
> >> Then I used the wrong terminology 'main sequence'.
>
> >> I meant their lineage and origin does not follow that of our familiar
> >> ancient stars, but they are, as you seem to agree, accidental products
> >> of "collapsing gas and dust" (oh, my!) of contemporary ancient stars.
> >>> Stars are made of baryonicv matter.
>
> >There's still quite a bit of primodial hydrogen and
> >helium hanging around in the galaxy that can form
> >new stars without too much in the way of "metal"
> >contamination from previous generations.
>
> These clouds have the makings of a cleancut, landmark test to finally
> validate general relativity. GR should define and quantify the exact
> cause for an implosion of this gaseous detrita, vigorous enough to
> register on our cameras, and to, at least, solder the particles
> together, if not to glow for a long time. (and twinkle).
> I don't rule it out, but it still fails the numbers criterion: circa
> 10^22.
> John Polasek
That's true enough about those 10e22 invisible stars, if not a heck of
a lot more when we're not permitted to mention black dwarfs and
apparently billions of those pesky black holes (perhaps each BH
containing a core of antimatter).
However, the original focus of this topic was relatively narrow, as to
the number of humanly visible stars belonging to our Milky Way. I say
that it's perhaps all of 0.0001% from the 5e11 to 1e12, meaning that
at best we can detect perhaps all of 500,000 to possibly a million out
of the total (including all the dark/black stuff, or UV stuff that's
also part of our galaxy).
. - Brad Guth
Androcles
"Steve Willner" <wil...@cfa.harvard.edu> wrote in message
news:fvo3d6$og4$1...@registered.motzarella.org...
| [deleted newsgroup sci.physics]
|
| In article
<a1bae604-910a-47b6...@z24g2000prf.googlegroups.com>,
| "B.T.World" <btrw...@yahoo.com> writes:
| > With 100 - 200 billion stars in our Milky Way, how many can we see?
| > With the naked eye, I think we can see several thousand.
|
| Good estimate. Probably around 6500 counting both hemispheres, all
| times of year, and assuming good eyesight and dark skies. The exact
| number depends on what "good eyesight" means; some people with
| extraordinary eyesight could probably see more.
Fair comment.
|
| > With good amateur telescopes, I assume maybe hundreds
| > of thousands or maybe even millions.
|
| "Good amateur telescopes" have gotten a lot better in the last few
| years. Also, it depends on whether you mean "with the naked eye" or
| if you allow photography or (even better) long exposures with CCD
| cameras. It would take some actual work to make a real estimate, but
| even for strictly visual observing through a 10-inch or so telescope,
| it looks as though there would be tens of millions of stars visible.
| (At the Galactic poles, there are about 100 stars per square degree
| brighter than mag 14.)
Fair comment.
Yes. Hubble is a telescope that relies on reflecting photons onto a pixel
array. Typically such an array contains about 1,000,000 pixels, often
1024 x 1024 about the same as your computer monitor.
This image of a single large star was captured by a portion of that array
from HST.
http://www.androcles01.pwp.blueyonder.co.uk/Orbit/mira_hst.jpg
From that we notice some pixels are brighter than others (the image
of the star fades at the boundary) and may hide stars on the same line
of sight which are fainter. The magnification is a ratio of the area
of sky to the area of the array. Given the actual data it is a simple
matter to compute the time required for the exposure of Mira
(a function of luminosity) multiplied by the area of the sky shown
and from that compute the time required to map the entire sky
at that same resolution.
| Existing star catalogs, as someone mentioned, contain a much smaller
| fraction than this.
|
| > E.g. blocked by the black hole at the center
|
| The black hole is tiny in comparison with the size of the galaxy. I
| doubt it blocks even a single star.
Assumes existence of the supposed critter. Here be dragons.
As always, the dragons are just beyond our reach, but when
we explore the regions where they live they fail to appear or
turn out to be something entirely different.
http://en.wikipedia.org/wiki/Here_be_dragons
There are enough mysteries to explore without artificially creating
new ones. Black holes are merely dragons of human invention.
Sam Wormley
> On Mon, 05 May 2008 16:59:55 GMT, Sam Wormley <swor...@mchsi.com>
> wrote:
>
>> John C. Polasek wrote:
>>> On Mon, 05 May 2008 02:37:59 GMT, Sam Wormley <swor...@mchsi.com>
>>> wrote:
>>>> There are many stars recently born in stellar birthing regions
>>>> of our galaxy... big suckers that live for just a few million
>>>> years... obviously younger than our sun that we measure the
>>>> luminosity and spectra of. Visible, yes!
>>>>
>>> Many, but not enough. These are not main sequence stars. They are
>>> accidental products of already existent older stars.
>>> I am talking about the 95% that are "dark matter", in number about
>>> 10^22.
>> Yes they are main sequence stars formed from collapsing gas and
>> of wave lengths.
> Then I used the wrong terminology 'main sequence'.
Stars are mostly hydrogen and helium. All stars spend the majority
of their lives on the "main sequence" fusing hydrogen into helium.
http://en.wikipedia.org/wiki/Main_sequence
>
> I meant their lineage and origin does not follow that of our familiar
> ancient stars, but they are, as you seem to agree, accidental products
> of "collapsing gas and dust" (oh, my!) of contemporary ancient stars.
>> Stars are made of baryonicv matter.
>>
>> Dark matter is tenuous enough that is clumps only on extragalactic
>> scales... Dark Matter gravitation is measured by the motions in and
>> of galaxies and gravitational lensing.
>
> Your two declarative sentences lead me to believe that you endorse
> these searches for WIMPs, MACHO's and neutralino's, all presently
> undefined, yet adequately funded. Do you?
I proffer no position on WIMPs, MACHOs or Neutralinos. Funding
requests typically go through review processes.
John C. Polasek
wrote:
Sam, you generally defend the status quo, but I claim physics is in as
desperate a shape as it's ever been. It cannot solve the Pioneer
anomaly, nor the dark matter problem nor has it a valid model for
gravity.
It seems as if, whenever a problem or paradox occurs, recourse is made
automatically to a new "particle" that has no more credibility than
phlogiston.
You demur, but 'give a pass' to WIMPs, MACHOs and neutralinos, etc.
inasmuch as they have survived a "peer review" process. This is not a
reasonable stance, as witness the following particles and concepts
from titles in one issue of Phys Rev D for April 15th which, we are to
believe, must have passed peer review:
Gluelump spectrum,
Leptoquarks,
diphoton,
littlest Higgs Zh,
anyons,
chirplet chains,
charmonium,
pomeron,
baby Skyrmion lattices,
pentaquark,
parton
You should review the whole index with catchy titles like
"Minimal seesaw as an ultraviolet-insensitive cure for anomalies"
"Weak productions of new charmonium in semileptonic decays of Bc".
"Quark condensates in the chiral bag with the Nambu-Jona-Lasinio
interaction".
It seems clear that none of the "peers" could know enough about most
of these specialized topics to judge any of them, and it is unlikely
that any author ever read anyone else's paper.
When I submitted a paper detailing the ep+ pair content of pairspace
that made permittivity possible, it was rejected and I was told my
stuff was not up to their standard.
These journals are about making money and the investigators are about
getting grants. There is a high cost to getting a paper published,
which is borne by the school or the NSF. Now one journal is allowing
an author to pay $975 as compensation for making his paper "free to
view".
Yes, I think physics is in desperate shape. It appears the heirarchy
are torpidly wallowing in their self-assurance.
John Polasek
Greg Neill
> Yes, I think physics is in desperate shape. It appears the heirarchy
> are torpidly wallowing in their self-assurance.
People gripe about supposedly dogmatic "status quo"
physics and then complain about the constantly published
more speculative research in practically the same breath.
What's up with that?
BradGuth
> "John C. Polasek" <jpola...@cfl.rr.com> wrote in messagenews:kfp024dr4tcuh7eo8...@4ax.com
>
> > Yes, I think physics is in desperate shape. It appears the heirarchy
> > are torpidly wallowing in their self-assurance.
>
> People gripe about supposedly dogmatic "status quo"
> physics and then complain about the constantly published
> more speculative research in practically the same breath.
> What's up with that?
If you're an insider of the status quo, you create as many bogus
topics as you can. It's what brown-nosed minions as clowns of the
status quo do best.
. - Brad Guth
Crown-Horned Snorkack
>
> "B.T.World" <btrwo...@yahoo.com> writes:
> > With 100 - 200 billion stars in our Milky Way, how many can we see?
> > With the naked eye, I think we can see several thousand.
>
> Good estimate. Probably around 6500 counting both hemispheres, all
> times of year, and assuming good eyesight and dark skies. The exact
> number depends on what "good eyesight" means; some people with
> extraordinary eyesight could probably see more.
>
> > With good amateur telescopes, I assume maybe hundreds
> > of thousands or maybe even millions.
>
> "Good amateur telescopes" have gotten a lot better in the last few
> years. Also, it depends on whether you mean "with the naked eye" or
> if you allow photography or (even better) long exposures with CCD
> cameras. It would take some actual work to make a real estimate, but
> even for strictly visual observing through a 10-inch or so telescope,
> it looks as though there would be tens of millions of stars visible.
> (At the Galactic poles, there are about 100 stars per square degree
> brighter than mag 14.)
>
is 129600 divided by pi), so 4 millions plus the milky way... how many
of those are in the Milky Way galaxy? Or asked differently, how many
aren´t?
> > With space telescopes such as Hubble, I assume we could see
> > billions.
>
> There are at least three problems than limit the number of Milky Way
> stars we can see. In all cases, it would take some work to do a real
> calculation, but I think in principle it could be done. Numbers
> below are my best guesses without calculating anything, but I may be
> grossly wrong.
>
> 1. Some stars are simply too faint and far away. Typical exposures
> with Hubble might reach magnitude 25. With this sensitivity, and if
> nothing else mattered, the Sun would be easily visible on the far
> edge of the Galaxy.
Roughly 100 000 parsecs. So, we can see sunlike stars in Magellanic
clouds. But not in Andromeda.
> The longest Hubble exposures, such as the famous
> Hubble Deep Field, can go quite a bit fainter than this. Most stars,
> however, are fainter than the Sun. The faintest of all are something
> like 10000 times fainter.
There should be a definite minimum brightness of a red dwarf - a bit
dimmer than Proxima, but precisely how much dimmer? Then again, young
brown dwarfs look much like red dwarfs. Are brown dwarfs stars?
A star 10 000 times fainter than Sun is magnitude 25 at 1000 parsecs.
There are, for example, no globular clusters within 2000 pc... can red
dwarfs be seen in globular clusters?
And then there are stars which are considerably smaller than red and
brown dwarfs, even though they may be hotter. Old white dwarfs and old
neutron stars. How hot and how bright is an old "white" dwarf? How hot
and how bright is an old, non-pulsar neutron star?
> I'm guessing well under 10% of all Milky
> Way stars are bright enough to be seen in typical Hubble exposures.
>
> 2. The Milky Way contains vast quantities of dust -- small solid
> particles. You can easily see foreground dust clouds in wide-field
> images of the Milky Way or with your naked eye if you look on a dark
> night. Because both stars and dust are concentrated to the Galactic
> plane, the dust probably blocks more than 90% of the stars that would
> otherwise be visible.
>
How much of the whole outer space is invisible because of dust?
> 3. When two or more stars are close together on the sky, observations
> may not be able to "resolve" or separate them. The obvious example
> of this is the Milky Way itself, which looks like a solid band of
> light to the naked eye but is really made up of the summed light of
> many stars. (The generic term for inability to resolve multiple
> sources is "confusion.") With a good telescope, or even binoculars,
> you can begin to see the Milky Way stars separately.
Yes, but binoculars and telescopes brighten the stars as well.
For example consider Praesepe. Magnitude 3,7 or so. It is visible.
But if Praesepe were more scattered, none of the stars could be seen -
the brightest of them is 6,6. They would all be lost in dark sky.
So... how many stars, brighter than 6,0, are within 60 arcseconds of
another star brighter than that, exclusive of physical doubles? This
could indicate how many stars are lost to confusion in addition to
6000 or so visible stars?
Sam Wormley
> Sam, you generally defend the status quo, but I claim physics is in as
> desperate a shape as it's ever been. It cannot solve the Pioneer
> anomaly, nor the dark matter problem nor has it a valid model for
> gravity.
I'm all for new insights and understanding, John, but I can't
see throwing away perfectly useful and fruitful tools just
because we are working on some pretty cool problems in physics.
There is little reason to suspect a problem with GTR concerning
the Pioneer data.... you should know that.
> It seems as if, whenever a problem or paradox occurs, recourse is made
> automatically to a new "particle" that has no more credibility than
> phlogiston.
There are plenty of theories predicting "new" particles... most
are likely wrong... some may turn out to be right... Science is
a process for finding out more about nature... embrace the process!
-Sam
John C. Polasek
wrote:
>John C. Polasek wrote:
>
>> Sam, you generally defend the status quo, but I claim physics is in as
>> desperate a shape as it's ever been. It cannot solve the Pioneer
>> anomaly, nor the dark matter problem nor has it a valid model for
>> gravity.
>
> I'm all for new insights and understanding, John, but I can't
> see throwing away perfectly useful and fruitful tools just
> because we are working on some pretty cool problems in physics.
Challenge: pick out one article from Phys Rev D that you find most
interesting, and give us a summary. You can't do it. It's all
poppycock, and it's a scandal.
> There is little reason to suspect a problem with GTR concerning
> the Pioneer data.... you should know that.
Yes there is; it's GR's geometry which in cosmology reflects a
universe with no center, no center of mass, sufficiently described
with a = a0/1+z, having no interesting geometry whatsoever. It came
from 4D GR, and it put a pall over cosmology. The BB (tee hee) had the
virtue of having a center but it too is abandoned, despite everyone's
thinking. (I have a replacement).
>
>> It seems as if, whenever a problem or paradox occurs, recourse is made
>> automatically to a new "particle" that has no more credibility than
>> phlogiston.
>
>
> There are plenty of theories predicting "new" particles... most
> are likely wrong... some may turn out to be right... Science is
> a process for finding out more about nature... embrace the process!
My original complaint was that I have found that dark matter can be
explained by geometry, which should be published, but from previous
experience with Phys Rev D. and from inspection of its current
content, I am betting against that possibility. (Don't rock their
boat).
Rather than searching for valid physics to explain dark matter, the
particle worshippers fund teams 1000's of feet below, with casks of
Xenon gas, striving to be the first to detect a spark from a WIMP.
(Others are hunting the Higgs boson with the 28km LHC vacuum doughnut,
and the graviton and the othertrons I listed).
> -Sam
John Polasek
B.T.World
>
> | Existing star catalogs, as someone mentioned, contain a much smaller
> | fraction than this.
> |
> | > E.g. blocked by the black hole at the center
> |
> | The black hole is tiny in comparison with the size of the galaxy. I
> | doubt it blocks even a single star.
>
> Assumes existence of the supposed critter. Here be dragons.
> As always, the dragons are just beyond our reach, but when
> we explore the regions where they live they fail to appear or
> turn out to be something entirely different.
> http://en.wikipedia.org/wiki/Here_be_dragons
> There are enough mysteries to explore without artificially creating
> new ones. Black holes are merely dragons of human invention.
No black hole at the center? Is not a lot of the mass of our
galaxy concentrated near the center, which may include a
'massive' black hole or could be something like a huge and very
very dense ball of stars within e.g. 1000 to 5000 light years
from the galactic center? Does not that keep the rest such
as the spiral arms from slowly spinning off into wider space
and leaving the galaxy?
What is roughly the rotational speed of our galaxy?
And is this rotational speed constant, i.e. is the tangential
velocity of the outer stars at 50,000 light years from the
center twice the tangential velocity of the sun at roughly
25,000 light years from the center?
Thanks,
B.T.
BradGuth
> On Tue, 06 May 2008 03:42:57 GMT, Sam Wormley <sworml...@mchsi.com>
> wrote:
>
>
>
> >John C. Polasek wrote:
> >> wrote:
>
> >>> John C. Polasek wrote:
It's a DARPA game that's pretty much stacked on behalf of favoring the
Yiddish and thus Old Testament point of view, or if you like mindset.
. - Brad Guth
Steve Willner
SW> brighter than mag 14.)
In article <d2be5527-ab31-4c63...@k13g2000hse.googlegroups.com>,
Crown-Horned Snorkack <chorned...@hush.ai> writes:
> And there are what, about 40 000 square degrees of sky
As you say, there are 4 pi steradians, and each steradian is
(180/pi)^2 square degrees, so about 41253 square degrees of sky.
40000 is certainly close enough for present purposes.
> how many of those are in the Milky Way galaxy?
All of them, or nearly so. There are a few Magellanic cloud stars
brighter than this limit and _maybe_ a very few M31/33 stars, but I
bet we are talking dozens or at most a few hundred. (I admit I have
not bothered to look up the correct number.)
> Roughly 100 000 parsecs. So, we can see sunlike stars in Magellanic
> clouds. But not in Andromeda.
Distance modulus of M31 (and M33) is about 24.4, so stars would have
to have absolute magnitude near 0 to be visible in typical HST
images. That corresponds to main sequence spectral type around B8.
Magellanic cloud distance modulus is about 18.7, so absolute
magnitude 6 stars should be visible to Hubble. That's about K0 or
K2 on the main sequence, maybe 3/4 of a solar mass.
> There should be a definite minimum brightness of a red dwarf - a bit
> dimmer than Proxima, but precisely how much dimmer?
The record-holder used to be VB 10 at M_v = 17.4, but I remember
reading a few years ago that a fainter star had been discovered.
Proxima has M_v = 15.5.
> Then again, young
> brown dwarfs look much like red dwarfs. Are brown dwarfs stars?
To some extent, it's a matter of semantics, but usually "stars" are
considered as objects that burn hydrogen, and brown dwarfs don't.
The most massive brown dwarfs burn deuterium, but that phase doesn't
last long because deuterium is so scarce.
> A star 10 000 times fainter than Sun is magnitude 25 at 1000 parsecs.
> There are, for example, no globular clusters within 2000 pc... can red
> dwarfs be seen in globular clusters?
Your calculation would suggest not, depending on what you mean by
"red dwarfs." In fact, it takes pretty long exposures to detect the
main sequence in globular clusters, and the brightest stars are (from
memory) about 0.8 solar masses.
> And then there are stars which are considerably smaller than red and
> brown dwarfs, even though they may be hotter. Old white dwarfs and old
> neutron stars. How hot and how bright is an old "white" dwarf? How hot
> and how bright is an old, non-pulsar neutron star?
Pretty faint! It would take some work, though, to dig up numbers.
You could try in ADS or even Google.
> How much of the whole outer space is invisible because of dust?
It depends on what wavelength you observe at and what are your
criteria for "invisible." There isn't a sharp boundary. Practical
extragalactic surveys often limit themselves to (absolute) Galactic
latitudes greater than 20 or 30 degrees, i.e., about 66% or 50% of
the sky, but extragalactic objects are known even at very low
latitudes. Radio observations are unaffected by dust, though they
are affected by Milky Way gas.
> So... how many stars, brighter than 6,0, are within 60 arcseconds of
> another star brighter than that, exclusive of physical doubles?
Not many. As you can work out from numbers above, on average there
are about 6.5 square degrees of sky per visible star (and even more
than that for V<6.0). If stars were distributed randomly, you
wouldn't even expect one pair so close.
Confusion is only important when there are many stars compared to
your instrumental angular resolution. A rule of thumb for when to
worry about confusion is 1/100 of a source per beam area (thus about
1% chance of having a second source in the same beam), but usually
the data aren't severely affected until you get to 1/40 of a source
per beam area.
Steve Willner
There's little doubt now; see
http://antwrp.gsfc.nasa.gov/apod/ap021018.html
for one easily understandable source.
> Is not a lot of the mass of our galaxy concentrated near the
> center,
About 2.6 million solar masses within a radius of about 17
light-hours. (There may be more stringent limits by now.) If this
isn't a black hole, it's something even weirder.
Of course 2.6 million solar masses is not a very big fraction of the
mass of the Milky Way or even of its bulge alone. Most of the mass
is stars; about 10% is gas.
> What is roughly the rotational speed of our galaxy?
About 200 km/s near the Sun. According to an older source, it seems
to rise slowly from inner to outer regions. A recent paper says it
falls slowly. (See Fig. 15 of http://arxiv.org/pdf/0801.1232v4 .)
No doubt there is more work to be done on this subject.
BradGuth
The gravity/tidal reach of the Milky Way is far greater than 50,000
light years, worth at the very least 4r, though perhaps a mutual tidal
pull between a pair of galaxies can become worth as great as 1024r,
would make this mutual tidal grasp of our Milky Way worthy of 51.2
million light years.
For one interesting example of a tight kind of tidal grasp, the
Tadpole galaxy tail is worth something greater than 300,000 ly.
Even though there are many galaxy groups, the average intergalactic
separation is typically far greater than 1024r
http://en.wikipedia.org/wiki/Galaxy
"Most galaxies in the universe are gravitationally bound to a number
of other galaxies. These form a fractal-like hierarchy of clustered
structures, with the smallest such associations being termed groups."
. - Brad Guth
BradGuth
Ever notice how these Usener/Groups of such a Jewish (aka Old
Testament) mindset don't want folks like yourself to count stars or
much less understand anything?
. - Brad Guth
Crown-Horned Snorkack
> SW> (At the Galactic poles, there are about 100 stars per square degree
> SW> brighter than mag 14.)
>
> Crown-Horned Snorkack <chornedsnork...@hush.ai> writes:
>
> > And there are what, about 40 000 square degrees of sky
>
> As you say, there are 4 pi steradians, and each steradian is
> (180/pi)^2 square degrees, so about 41253 square degrees of sky.
> 40000 is certainly close enough for present purposes.
>
> > how many of those are in the Milky Way galaxy?
>
> All of them, or nearly so. There are a few Magellanic cloud stars
> brighter than this limit and _maybe_ a very few M31/33 stars, but I
> bet we are talking dozens or at most a few hundred. (I admit I have
> not bothered to look up the correct number.)
>
> > Roughly 100 000 parsecs. So, we can see sunlike stars in Magellanic
> > clouds. But not in Andromeda.
>
> Distance modulus of M31 (and M33) is about 24.4, so stars would have
> to have absolute magnitude near 0 to be visible in typical HST
> images. That corresponds to main sequence spectral type around B8.
>
> Magellanic cloud distance modulus is about 18.7, so absolute
> magnitude 6 stars should be visible to Hubble. That's about K0 or
> K2 on the main sequence, maybe 3/4 of a solar mass.
>
> > There should be a definite minimum brightness of a red dwarf - a bit
> > dimmer than Proxima, but precisely how much dimmer?
>
> The record-holder used to be VB 10 at M_v = 17.4, but I remember
> reading a few years ago that a fainter star had been discovered.
> Proxima has M_v = 15.5.
>
else young brown dwarfs?
> > Then again, young
> > brown dwarfs look much like red dwarfs. Are brown dwarfs stars?
>
> To some extent, it's a matter of semantics, but usually "stars" are
> considered as objects that burn hydrogen, and brown dwarfs don't.
Neither do white dwarfs.
> The most massive brown dwarfs burn deuterium, but that phase doesn't
> last long because deuterium is so scarce.
>
> > A star 10 000 times fainter than Sun is magnitude 25 at 1000 parsecs.
> > There are, for example, no globular clusters within 2000 pc... can red
> > dwarfs be seen in globular clusters?
>
> Your calculation would suggest not, depending on what you mean by
> "red dwarfs." In fact, it takes pretty long exposures to detect the
> main sequence in globular clusters, and the brightest stars are (from
> memory) about 0.8 solar masses.
>
Brightest stars in globular clusters, or brightest stars in the main
sequence of globular clusters?
BradGuth
wrote:
At best 0.0001% of our visual spectrum worthy stars within the Milky
Way can be seen by the optically enhanced human eye. That only leaves
99.9999% as hidden or otherwise obscured from the human view of our
limited visual spectrum as we know it. Of course IR and UV stars are
nearly if not entirely invisible to the human visual spectrum.
. - Brad Guth
B.T.World
> In article <7c3ba079-c689-4892-88b1-1047323c9...@q1g2000prf.googlegroups.com>,> There's little doubt now; seehttp://antwrp.gsfc.nasa.gov/apod/ap021018.html
> for one easily understandable source.
>
> > Is not a lot of the mass of our galaxy concentrated near the
> > center,
>
> About 2.6 million solar masses within a radius of about 17
> light-hours. (There may be more stringent limits by now.) If this
> isn't a black hole, it's something even weirder.
>
> Of course 2.6 million solar masses is not a very big fraction of the
> mass of the Milky Way or even of its bulge alone. Most of the mass
> is stars; about 10% is gas.
>
> > What is roughly the rotational speed of our galaxy?
>
> About 200 km/s near the Sun. According to an older source, it seems
> to rise slowly from inner to outer regions. A recent paper says it
> falls slowly. (See Fig. 15 ofhttp://arxiv.org/pdf/0801.1232v4.)
> No doubt there is more work to be done on this subject.
>
> --
> Cambridge, MA 02138 USA
> (Please email your reply if you want to be sure I see it; include a
> valid Reply-To address to receive an acknowledgement. Commercial
> email may be sent to your ISP.)
Thanks for your answers.
There seems to be a lot we don't know (yet) about our galaxy.
BradGuth
That's very true, in that all of 1e-6th of our Milky Way stars have
been detected by the human eye (that's including those detected within
our visual spectrum along with the added help of KECK and Hubble)
Outside of our best swag, imagine what little we really know about our
mostly expanding universe.
. - Brad Guth
Painius
news:70b50aca-7f94-4a0e...@e53g2000hsa.googlegroups.com...
That's true except for a rather large area on the other
side of the galaxy...
http://www.atlasoftheuniverse.com/milkyway.html
(Look toward the bottom of the page under: The Shape
of the Milky Way - The Evidence")
We have little to no idea what resides in that area of the
galaxy or beyond.
happy days and...
starry starry nights!
--
Indelibly yours,
Paine
P.S. Thank YOU for reading!
P.P.S. Some secret sites (shh)...
http://painellsworth.net
http://savethechildren.org
http://eBook-eDen.secretsgolden.com
Steve Willner
Crown-Horned Snorkack <chorned...@hush.ai> writes:
SW> ...it takes pretty long exposures to detect the main sequence in
SW> globular clusters, and the brightest stars are (from memory)
SW> about 0.8 solar masses.
> Brightest stars in globular clusters, or brightest stars in the main
> sequence of globular clusters?
Both. The red giant phase is very short compared to the time spent
on the main sequence, so the giant stars in a gc are only a tiny
amount more massive than the brightest main sequence stars.
> How are faint stars verified as being either genuine red dwarfs or
> else young brown dwarfs?
From spectroscopy or (with less certainty) from broadband colors. As
you imply, for very young objects, it may be hard to be certain.
SW> > To some extent, it's a matter of semantics, but usually "stars" are
SW> > considered as objects that burn hydrogen, and brown dwarfs don't.
> Neither do white dwarfs.
I should have written "objects that burn hydrogen at some time during
their lives." Still, it would be merely unpopular, not ridiculous,
to define white dwarfs as not being stars. That's what I meant by
"semantics." White dwarfs are quite different from hydrogen-burning
stars, despite having comparable masses. The word "stars" is
understood as including both, but the language might have turned out
otherwise.
Crown-Horned Snorkack
> In article <8081a07e-115c-4e7c-b78f-7d8b3719f...@25g2000hsx.googlegroups.com>,
> Crown-Horned Snorkack <chornedsnork...@hush.ai> writes:
> SW> ...it takes pretty long exposures to detect the main sequence in
> SW> globular clusters, and the brightest stars are (from memory)
> SW> about 0.8 solar masses.
>
> > Brightest stars in globular clusters, or brightest stars in the main
> > sequence of globular clusters?
>
> Both. The red giant phase is very short compared to the time spent
> on the main sequence, so the giant stars in a gc are only a tiny
> amount more massive than the brightest main sequence stars.
>
When do red giants lose mass? Do they lose mass suddenly when they
stop being red giants and become planetary nebulae, or do they lose
mass over long time, so that red giants are already less massive than
main sequence stars?
Also, where are the farthest double stars which can be both resolved
into components and observed moving on orbits?
> > How are faint stars verified as being either genuine red dwarfs or
> > else young brown dwarfs?
>
> From spectroscopy or (with less certainty) from broadband colors. As
> you imply, for very young objects, it may be hard to be certain.
>
> SW> > To some extent, it's a matter of semantics, but usually "stars" are
> SW> > considered as objects that burn hydrogen, and brown dwarfs don't.
>
> > Neither do white dwarfs.
>
> I should have written "objects that burn hydrogen at some time during
> their lives." Still, it would be merely unpopular, not ridiculous,
> to define white dwarfs as not being stars. That's what I meant by
> "semantics." White dwarfs are quite different from hydrogen-burning
> stars, despite having comparable masses. The word "stars" is
> understood as including both, but the language might have turned out
> otherwise.
>
Yes. When the question arises as to how many stars exist in the Galaxy
and how many stars we can see in Galaxy, or what the dimmest stars
are, we have to clarify what are or are not stars.
How many objects can we see in Galaxy that are not stars?
BradGuth
wrote:
The human eye can't see hardly squat. It takes extremely complex and
spendy technology in order that a thousand fold more can be detected,
and even that's not worth 0.1% of what our Milky Way has to offer.
Of what's beyond our home galaxy is pretty much limited to the
capability of applied technology, as otherwise we'd not be aware of
such things other than the most massive of other nearby galaxies.
. - Brad Guth
Steve Willner
SW> on the main sequence, so the giant stars in a gc are only a tiny
SW> amount more massive than the brightest main sequence stars.
In article <0ff5a7eb-a9e5-4bc2...@d1g2000hsg.googlegroups.com>,
Crown-Horned Snorkack <chorned...@hush.ai> writes:
> Are they more massive at all?
If you are talking about _original_ masses, then statistically
probably yes but by something well under 0.01 solar masses at a rough
guess. Not every individual giant star will be more massive than
every main sequence star. (And I'm ignoring blue stragglers
altogether.)
> When do red giants lose mass?
Here, though, you raise a good point. Giant stars lose mass at some
level throughout that phase of evolution, so stars on the giant
branch probably are less massive than the most massive main sequence
stars.
> Do they lose mass suddenly when they
> stop being red giants and become planetary nebulae, or do they lose
> mass over long time, so that red giants are already less massive than
> main sequence stars?
Probably both, though I don't think the details are well known. I am
sure the details depend on mass and probably also on metallicity. As
indicated above, there is very likely mass loss all during the giant
phase and also there are likely to be episodes when the mass loss is
much greater than normal. These could occur when the star goes
through phases of pulsational instability. There are probably upper
limits on total mass loss from inability to detect dust in cluster
cores.
It would take some work to track down what is and is not known, and I
could easily be unaware of recent results.
> Also, where are the farthest double stars which can be both resolved
> into components and observed moving on orbits?
This would also take some work to find out, but I'd guess within a
few hundred parsecs. I think there are only a few hundred systems
that are both visual and spectroscopic binaries.
> How many objects can we see in Galaxy that are not stars?
Another question that would take some work, depending on your
definition of "see." There are tens of thousands of numbered minor
planets and of course quite a few other solar system objects such as
comets and satellites, not to mention 8 planets. About 300
exoplanets, I think. Many dozens of brown dwarfs, maybe hundreds by
now. The black hole at the Milky Way center. Gaseous nebulae and
molecular clouds, probably thousands. Probably other things I'm not
thinking of right now. Anybody else want to chime in?
Crown-Horned Snorkack
> SW> Both. The red giant phase is very short compared to the time spent
> SW> on the main sequence, so the giant stars in a gc are only a tiny
> SW> amount more massive than the brightest main sequence stars.
>
> Crown-Horned Snorkack <chornedsnork...@hush.ai> writes:
>
> > Are they more massive at all?
>
> If you are talking about _original_ masses, then statistically
> probably yes but by something well under 0.01 solar masses at a rough
> guess. Not every individual giant star will be more massive than
> every main sequence star. (And I'm ignoring blue stragglers
> altogether.)
>
> > When do red giants lose mass?
>
> Here, though, you raise a good point. Giant stars lose mass at some
> level throughout that phase of evolution, so stars on the giant
> branch probably are less massive than the most massive main sequence
> stars.
>
> > Do they lose mass suddenly when they
> > stop being red giants and become planetary nebulae, or do they lose
> > mass over long time, so that red giants are already less massive than
> > main sequence stars?
>
> Probably both, though I don't think the details are well known. I am
> sure the details depend on mass and probably also on metallicity. As
> indicated above, there is very likely mass loss all during the giant
> phase and also there are likely to be episodes when the mass loss is
> much greater than normal. These could occur when the star goes
> through phases of pulsational instability. There are probably upper
> limits on total mass loss from inability to detect dust in cluster
> cores.
>
of supernovae (of first kind)?
What do red giants lose? Unfused hydrogen? Helium? Metals? And if any
metals are lost (rather than staying in the white dwarfs), do carbon,
oxygen and nitrogen stay as vapour in interstellar space, or condense
into snow?
> It would take some work to track down what is and is not known, and I
> could easily be unaware of recent results.
>
> > Also, where are the farthest double stars which can be both resolved
> > into components and observed moving on orbits?
>
> This would also take some work to find out, but I'd guess within a
> few hundred parsecs. I think there are only a few hundred systems
> that are both visual and spectroscopic binaries.
>
> > How many objects can we see in Galaxy that are not stars?
>
> Another question that would take some work, depending on your
> definition of "see."
And definitions of "many", "Galaxy" and "star".
There are tens of thousands of numbered minor
> planets and of course quite a few other solar system objects such as
> comets and satellites, not to mention 8 planets.
We notoriously managed to not see Eris and Quaoar till very recently.
How many objects are bigger than Eris and closer than Proxima, that we
do not see? I do not think we have seen anything at all between Sedna
and Proxima. We probably would have seen something as big as Jupiter
within the distance to Edna, but going smaller or farther, not sure
how complete the map is...
About 300
> exoplanets, I think.
Has any body outside the orbit of Neptune been confirmed as having
"cleared an orbit"?
Many dozens of brown dwarfs, maybe hundreds by
> now.
How do we tell apart "brown dwarfs" from "exoplanets"?
The black hole at the Milky Way center. Gaseous nebulae and
> molecular clouds, probably thousands.
And how do you distinguish neighbouring clouds from parts of an odd-
shaped cloud? At least stars have good physical reasons to be
discrete, countable objects.
BradGuth
> "BradGuth" <bradg...@gmail.com> wrote in message
We can't even find terrestrial WMD, much less deal with the likely 500
billion if not a trillion stars of UV to deep IR status within our
Milky Way.
What's our orbital status or mutual tidal radius with Sirius?
. - Brad Guth
Steve Willner
Crown-Horned Snorkack <chorned...@hush.ai> writes:
> Do globular clusters normally contain planetary nebulae
I haven't heard of any, but I don't see why they couldn't be present.
PN lifetimes are fairly short, so there shouldn't be very many, and
They wouldn't be easy to detect. There may be some I don't know
about; I am no expert on this subject!
> and remnants of supernovae (of first kind)?
You mean "Type 1" (result of accretion onto a white dwarf)? One
would think blue stragglers leaving their main sequence would be
candidates to make SNe. I don't know of any SN remnants in GCs,
though, and they should be easy to detect by radio observations if
they exist. I'm wondering how long they would last in a cluster
environment. Or maybe nobody has looked. Or maybe I'm just wrong
about blue stragglers creating them, or at least they aren't created
very often. See above remark about "no expert."
> What do red giants lose?
Whatever is on the surface. For stars much below a solar mass, the
surface convection layer is pretty deep, so it will bring nuclear-
burning products to the surface. More massive stars are complicated;
sometimes nuclear-burning products are brought to the surface and
sometimes not, depending on the exact mass and metallicity.
> If metals are lost (rather than staying in the white dwarfs), do carbon,
> oxygen and nitrogen stay as vapour in interstellar space, or condense
> into snow?
They condense into dust, principally silicates for oxygen-rich stars
and graphite for carbon-rich stars. The dust is prominent in the
infrared spectra of mass-losing stars, and this process is a major
contributor to dust creation. (Novae and supernovae are the other
major dust creators.)
> Has any body outside the orbit of Neptune been confirmed as having
> "cleared an orbit"?
Note that the definition of "planet" applies only within the solar
system. Nevertheless, many exoplanets are large enough to have
cleared their orbits according to theory. There are also
protoplanetary disks where gaps can be detected, presumably created
by planets that cannot be directly observed.
> How do we tell apart "brown dwarfs" from "exoplanets"?
By mass, I think, though no doubt there is some question where the
boundary should be. At some level this is a semantic question, not a
physical one.
> And how do you distinguish neighbouring clouds from parts of an odd-
> shaped cloud?
If you want to make a catalog, you will have to adopt some
operational definition. Most likely the definition you choose will
depend on your observational capabilities.
Crown-Horned Snorkack
> In article <bdbb0d45-cc3d-4bfa-865a-9c4e7bb3c...@c65g2000hsa.googlegroups.com>,
> Crown-Horned Snorkack <chornedsnork...@hush.ai> writes:
>
> > Do globular clusters normally contain planetary nebulae
>
> I haven't heard of any, but I don't see why they couldn't be present.
> PN lifetimes are fairly short, so there shouldn't be very many, and
> They wouldn't be easy to detect. There may be some I don't know
> about; I am no expert on this subject!
>
> > and remnants of supernovae (of first kind)?
>
> You mean "Type 1" (result of accretion onto a white dwarf)? One
> would think blue stragglers leaving their main sequence would be
> candidates to make SNe. I don't know of any SN remnants in GCs,
> though, and they should be easy to detect by radio observations if
> they exist. I'm wondering how long they would last in a cluster
> environment. Or maybe nobody has looked. Or maybe I'm just wrong
> about blue stragglers creating them,
Not blue stragglers, except in young globular clusters (absent in
Milky Way). If the maximum mass of main sequence and giant stars is 1
solar then most blue stragglers would derive from two stars and thus
be below 2 solar masses. Type II supernovas are more massive than
that.
or at least they aren't created
> very often. See above remark about "no expert."
>
> > What do red giants lose?
>
> Whatever is on the surface. For stars much below a solar mass, the
> surface convection layer is pretty deep, so it will bring nuclear-
> burning products to the surface. More massive stars are complicated;
> sometimes nuclear-burning products are brought to the surface and
> sometimes not, depending on the exact mass and metallicity.
>
> > If metals are lost (rather than staying in the white dwarfs), do carbon,
> > oxygen and nitrogen stay as vapour in interstellar space, or condense
> > into snow?
>
> They condense into dust, principally silicates for oxygen-rich stars
Where does the silicon come from?
> and graphite for carbon-rich stars.
Oops, forgot about graphite - it is indeed competitive with methane.
So you are going to have graphite dust in stellar winds.
Steve Willner
Crown-Horned Snorkack <chorned...@hush.ai> writes:
> Not blue stragglers, except in young globular clusters (absent in
> Milky Way). If the maximum mass of main sequence and giant stars is 1
> solar then most blue stragglers would derive from two stars and thus
> be below 2 solar masses. Type II supernovas are more massive than
> that.
I thought the discussion was about Type 1a SNe, and I'd expect blue
stragglers -- which were in the past mass-transfer binaries -- to be
prime candidates for those.
On thinking further, it seems to me that there just are not enough
stars in all the Milky Way globular clusters to expect to find a
supernova remnant at any random time.
> Where does the silicon come from?
Formed in past generations of massive stars, I'd expect. Anyway,
silicon is seen in stellar spectra, and its abundance seems to be
pretty well known.
> Oops, forgot about graphite - it is indeed competitive with methane.
> So you are going to have graphite dust in stellar winds.
Or perhaps more likely amorphous carbon, according to a talk I heard
yesterday. I'm not sure which should be there, but one or both must
be. (Emission is definitely present, but neither form of carbon has
distinct infrared spectral features.) There's also some silicon
carbide, which has a detectable spectral feature around 11 microns.
Probably minor amounts of lots of other things, too.
Crown-Horned Snorkack
> In article <b258c23b-2151-4b11-8714-06a22f218...@26g2000hsk.googlegroups.com>,
> Crown-Horned Snorkack <chornedsnork...@hush.ai> writes:
>
> > Not blue stragglers, except in young globular clusters (absent in
> > Milky Way). If the maximum mass of main sequence and giant stars is 1
> > solar then most blue stragglers would derive from two stars and thus
> > be below 2 solar masses. Type II supernovas are more massive than
> > that.
>
> I thought the discussion was about Type 1a SNe, and I'd expect blue
> stragglers -- which were in the past mass-transfer binaries -- to be
> prime candidates for those.
>
are in, or something else?
Type I supernova progenitors are supposed to be white dwarfs.
> On thinking further, it seems to me that there just are not enough
> stars in all the Milky Way globular clusters to expect to find a
> supernova remnant at any random time.
>
> > Where does the silicon come from?
>
> Formed in past generations of massive stars, I'd expect. Anyway,
> silicon is seen in stellar spectra, and its abundance seems to be
> pretty well known.
>
But the globular clusters are noted for having low metallicity -
little material from past generations of massive stars. The low mass
red giants - sunlike stars which are completing fusion now - are
thought to fuse helium, but not fuse carbon and oxygen into silicon.
Nicolaas Vroom
"Steve Willner" <wil...@cfa.harvard.edu> schreef in bericht
news:fvo3d6$og4$1...@registered.motzarella.org...
> [deleted newsgroup sci.physics]
>
>
> 3. When two or more stars are close together on the sky, observations
> may not be able to "resolve" or separate them. The obvious example
> of this is the Milky Way itself, which looks like a solid band of
> light to the naked eye but is really made up of the summed light of
> many stars. (The generic term for inability to resolve multiple
> sources is "confusion.") With a good telescope, or even binoculars,
> sufficiently large telescope above Earth's atmosphere could resolve
> each Milky Way star, but Hubble and other existing telescopes cannot
> do so. Many of the stars lost to confusion are the same ones lost
> because of dust extinction, but probably another factor of 3 to 5 are
> lost as well.
>
> Thus my *guess* is that if we could map the entire sky with Hubble
> (which would take what, thousands of years of observing time?), we
> could detect something like 1% of the Milky Way stars. As I caution
> above, this is a guess and may be wildly wrong. Anybody care to do a
> real calculation?
>
And what about the number of Jupiter sized planets we can detect ? 0.1 % ?
And what about the number of Pluto sized objects ? 0.01 % ?
And what is the error range ? 100 % ?
This makes me wonder.
Because it is so difficult based on what we actual can detect
(stars, planets, pluto sized objects) to calculate
the total mass of our galaxy, why is it that we are sure that in order
to simulate the rotation curve of our galaxy lots of dark matter
is required.
In effect by doing that we reduce the number of stars in our galaxy.
Nicolaas Vroom
http://users.pandora.be/nicvroom/
Steve Willner
Crown-Horned Snorkack <chorned...@hush.ai> writes:
> Are blue stragglers main sequence stars too heavy for the cluster they
> are in, or something else?
That's essentially it: stars apparently on the main sequence but more
luminous than the turnoff. There used to be several explanations,
but as I understand it, the mass-transfer binary explanation is now
pretty much accepted. That is, these systems started out as an
unequal-mass binary, then the more massive star became a red giant
and dumped some mass on the the originally less-massive star, which
(having not burned its own hydrogen very fast) remains a main
sequence star but more massive and thus hotter and brighter than the
turnoff.
There's more about blue stragglers at
http://curious.astro.cornell.edu/question.php?number=297
There's also a Wikipedia article, but some of the things in it don't
seem quite correct to me. It gives the basic idea, I guess.
http://apod.nasa.gov/apod/ap030808.html
is a nice picture, but the text seems to be touting collisions rather
than mass transfer. Perhaps I'm wrong, and it's collisions after
all. I don't work on this subject and just have some vague memories
of talks I've heard, and I don't have time to do an ADS search
through the literature. Maybe someone else will do it.
> Type I supernova progenitors are supposed to be white dwarfs.
My point exactly. The originally more-massive star becomes a white
dwarf, and it's in a close orbit around another star. Once that star
ages and starts losing mass, you would expect the system to be a
prime candidate to become a Type 1a supernova.
I think this process must happen but just not very often in globular
clusters, given the relatively small number of stars they contain.
> But the globular clusters are noted for having low metallicity -
> little material from past generations of massive stars. The low mass
> red giants - sunlike stars which are completing fusion now - are
> thought to fuse helium, but not fuse carbon and oxygen into silicon.
There's still some silicon from previous generations of star
formation, just not as much as in the Sun. But you are right to
think there will be _less_ dust generated in a low-metallicity
stellar outflow.
Steve Willner
"Nicolaas Vroom" <nicolaa...@pandora.be> writes:
> Because it is so difficult based on what we actual can detect
> (stars, planets, pluto sized objects) to calculate
> the total mass of our galaxy, why is it that we are sure that in order
> to simulate the rotation curve of our galaxy lots of dark matter
> is required.
Stellar mass can be measured both in the Milky Way and in other
galaxies. Likewise, rotation curves can be measured. The mass
indicated by the latter is much greater than indicated by the former,
so _either_ the theory of gravity is wrong _or_ there is a great deal
of mass in something that isn't stars and doesn't otherwise show up,
i.e., "dark matter."
Planets and "pluto sized objects" are examples of possible
constituents of dark matter. There are many others. For some
constituents, there are observational limits on how much mass they
can contribute. For others, there are no useful limits.
Crown-Horned Snorkack
> In article <64g%j.32138$cZ3.17...@newsfe10.ams2>,
> "Nicolaas Vroom" <nicolaas.vr...@pandora.be> writes:
>
> > Because it is so difficult based on what we actual can detect
> > (stars, planets, pluto sized objects) to calculate
> > the total mass of our galaxy, why is it that we are sure that in order
> > to simulate the rotation curve of our galaxy lots of dark matter
> > is required.
>
> Stellar mass can be measured both in the Milky Way and in other
> galaxies.
Down to which masses?
In the immediate solar neighbourhood, we have a rough idea about how
many red dwarfs exist (because we can see even the dimmest, like
Proxima) and how their numbers and combined mass compares to that of
orange and yellow dwarfs and bright main sequence stars. But do we
have any clue about what the situation is in other parts of Milky Way?
Steve Willner
SW> galaxies.
In article <2414971e-bcaf-4b9c...@34g2000hsf.googlegroups.com>,
Crown-Horned Snorkack <chorned...@hush.ai> writes:
> Down to which masses?
>
> In the immediate solar neighbourhood, we have a rough idea about how
> many red dwarfs exist (because we can see even the dimmest, like
> Proxima) and how their numbers and combined mass compares to that of
> orange and yellow dwarfs and bright main sequence stars. But do we
> have any clue about what the situation is in other parts of Milky Way?
As you indicate, the smallest-mass stellar objects can only be
surveyed locally. In the immediate solar neighborhood, the limit
extends into the brown dwarf range, but not so at larger distances.
In general, there's no reason to think the "mass function" in most
places differs from the local one. This is a complicated subject,
though, and there are some places where the mass function probably
does differ from the local one. Low-metallicity dwarf galaxies and
galaxies in the very early Universe are examples. More familiarly,
the mass function is definitely different in globular clusters, where
all the high-mass stars are gone.
If you are worried about differing mass functions in different
places, one approach is to consider low-mass stars a potential
constituent of dark matter, then try to set limits on what fraction
of the dark matter they could account for.
Nicolaas Vroom
> In article <64g%j.32138$cZ3....@newsfe10.ams2>,
> "Nicolaas Vroom" <nicolaa...@pandora.be> writes:
>> Because it is so difficult based on what we actual can detect
>> (stars, planets, pluto sized objects) to calculate
>> the total mass of our galaxy, why is it that we are sure that in order
>> to simulate the rotation curve of our galaxy lots of dark matter
>> is required.
>
> Stellar mass can be measured both in the Milky Way and in other
> galaxies. Likewise, rotation curves can be measured. The mass
> indicated by the latter is much greater than indicated by the former,
> so _either_ the theory of gravity is wrong _or_ there is a great deal
> of mass in something that isn't stars and doesn't otherwise show up,
> i.e., "dark matter."
>
> Planets and "pluto sized objects" are examples of possible
> constituents of dark matter. There are many others. For some
> constituents, there are observational limits on how much mass they
> can contribute. For others, there are no useful limits.
Accordingly to Wikepedia http://en.wikipedia.org/wiki/Dark_Matter
"The composition of dark matter is unknown but may include etc
astronomical bodies such as brown dwarfs and planets
(collectively called MACHOs), etc
Current evidence favors models in which the primary component of
dark matter is new elementary particles, collectively called
nonbaryonic dark matter."
Is this last true for our Galaxy ?
The following document about spiral galaxies from 1994 states:
http://nedwww.ipac.caltech.edu/level5/Sept01/Carr/Carr2_2.html
"One indication that halos are dominated by nonbaryonic material may"
IMO the most logical and simple explanation for a flat rotation curve
is that there are MACHOs in the disk and that there is no need of
a halo with nonbaryonic material.
Is this wrong and why.
Nicolaas Vroom
http://users.pandora.be/nicvroom/
Androcles
"Nicolaas Vroom" <nicolaa...@pandora.be> wrote in message
news:Qn64k.103480$SA7....@newsfe09.ams2...
|
| "Steve Willner" <wil...@cfa.harvard.edu> schreef in bericht
| news:g29heo$vm9$1...@registered.motzarella.org...
| > In article <64g%j.32138$cZ3....@newsfe10.ams2>,
| > "Nicolaas Vroom" <nicolaa...@pandora.be> writes:
| >> Because it is so difficult based on what we actual can detect
| >> (stars, planets, pluto sized objects) to calculate
| >> the total mass of our galaxy, why is it that we are sure that in order
| >> to simulate the rotation curve of our galaxy lots of dark matter
| >> is required.
| >
| > Stellar mass can be measured both in the Milky Way and in other
| > galaxies. Likewise, rotation curves can be measured. The mass
| > indicated by the latter is much greater than indicated by the former,
| > so _either_ the theory of gravity is wrong _or_ there is a great deal
| > of mass in something that isn't stars and doesn't otherwise show up,
| > i.e., "dark matter."
| >
| > Planets and "pluto sized objects" are examples of possible
| > constituents of dark matter. There are many others. For some
| > constituents, there are observational limits on how much mass they
| > can contribute. For others, there are no useful limits.
|
| Accordingly to Wikepedia http://en.wikipedia.org/wiki/Dark_Matter
| "The composition of dark matter is unknown but may
That says all it needs to about wackypedia.
Unknown and may.
Pigs may fly when they get wings, but then they'll be pigeons.
Either the theory of gravity is wrong or there is a great deal
of mass in something that is not stars or just maybe one other
possibility: crackpot theories about how light behaves means
it is NOT so easy to measure rotation.
Why did Einstein say
the speed of light from A to B is c-v,
the speed of light from B to A is c+v,
the "time" each way is the same?
Answer: because he was a crackpot and crackpots invent
dark matter.
1/2[tau(A)+tau(A')]= tau(B)
where
A = (0,0,0,t)
A' =(0,0,0,t+x'/(c-v) +x'/(c+v))
B = (x',0,0,t+x'/(c-v))
x' = x-vt
Ref: http://www.fourmilab.ch/etexts/einstein/specrel/www/figures/img22.gif
"Easy: he did NOT say that." - cretin harald.vanlin...@epfl.ch
According to moron van lintel, Einstein did not write the equation he wrote.
Androcles
Nicolaas Vroom
"Androcles" <Headm...@Hogwarts.physics> schreef in bericht
news:t_94k.156028$UP6.1...@newsfe14.ams2...
>
> "Nicolaas Vroom" <nicolaa...@pandora.be> wrote in message
> news:Qn64k.103480$SA7....@newsfe09.ams2...
> |
> | "Steve Willner" <wil...@cfa.harvard.edu> schreef in bericht
> | news:g29heo$vm9$1...@registered.motzarella.org...
> | > In article <64g%j.32138$cZ3....@newsfe10.ams2>,
> | > "Nicolaas Vroom" <nicolaa...@pandora.be> writes:
> | >> Because it is so difficult based on what we actual can detect
> | >> (stars, planets, pluto sized objects) to calculate
> | >> the total mass of our galaxy, why is it that we are sure that in
> order
> | >> to simulate the rotation curve of our galaxy lots of dark matter
> | >> is required.
> | >
> | > Stellar mass can be measured both in the Milky Way and in other
> | > galaxies. Likewise, rotation curves can be measured. The mass
> | > indicated by the latter is much greater than indicated by the former,
> | > so _either_ the theory of gravity is wrong _or_ there is a great deal
> | > of mass in something that isn't stars and doesn't otherwise show up,
> | > i.e., "dark matter."
> | >
> | > Planets and "pluto sized objects" are examples of possible
> | > constituents of dark matter. There are many others. For some
> | > constituents, there are observational limits on how much mass they
> | > can contribute. For others, there are no useful limits.
> |
> | Accordingly to Wikepedia http://en.wikipedia.org/wiki/Dark_Matter
> | "The composition of dark matter is unknown but may
>
> Unknown and may.
> Pigs may fly when they get wings, but then they'll be pigeons.
Snip
Sorry I do not understand what your reply has to do with darkmatter
i.e. MACHOs in the disc versus nonbaryonic material in the halo.
Nicolaas Vroom http://users.pandora.be/nicvroom/
Androcles
=============================================
snip
Sorry you do not understand what my reply has to do with your stupidity,
you snipping cretin, but I'll repeat it in case you ever wake up.
Nicolaas Vroom
"Androcles" <Headm...@Hogwarts.physics> schreef in bericht
>
> Either the theory of gravity is wrong or there is a great deal
Snip
Sorry again I do not understand what your reply about gravity
Androcles
you snipping cretin, but I'll repeat it in case you ever wake up.
Either the theory of gravity is wrong or there is a great deal
Steve Willner
"Nicolaas Vroom" <nicolaa...@pandora.be> writes:
> Accordingly to Wikepedia http://en.wikipedia.org/wiki/Dark_Matter
> "The composition of dark matter is unknown but may include etc
> astronomical bodies such as brown dwarfs and planets
> (collectively called MACHOs), etc
> Current evidence favors models in which the primary component of
> dark matter is new elementary particles, collectively called
> nonbaryonic dark matter."
> Is this last true for our Galaxy ?
This is rather confused. There are two types of dark matter:
baryonic and non-baryonic. The total amounts of each are known
(mainly from WMAP) but not the composition of either one. Most of
the dark matter is non-baryonic.
MACHOs are baryonic. What we can say is that MACHO searches so far
have not found nearly enough objects to account for even the baryonic
dark matter, but the searches are not sensitive to objects less
massive than of order a tenth of a solar mass (thus planets,
asteroids, cannon balls, etc.). The MACHO limits also depend on how
the dark matter is distributed.
New elementary particles would be expected to be non-baryonic. (I
don't know enough about particle physics to know whether new baryons
are even conceivable. I'm sure no one expects any!)
I'm afraid the real answer for now is "no one knows."
> IMO the most logical and simple explanation for a flat rotation curve
> is that there are MACHOs in the disk and that there is no need of
> a halo with nonbaryonic material.
> Is this wrong and why.
For MACHOs to populate only the disk, they would have to have formed
there, and it's hard to see what they could be. (If they are formed
along with stars, why wouldn't they also exist in the bulge and
halo?) Also, as noted, there are upper limits from MACHO searches,
in particular towards the Galactic bulge. There's also an argument
that spiral arms aren't stable without a massive halo, but I'm not
sure the arms have to be stable: maybe they are transient features.
In any case, there still needs to be non-baryonic dark matter to
account for the WMAP observations. If this matter interacts only by
gravity, it can't collapse into a disk.