Universe shines twice as bright (Forwarded)
Andrew Yee
University of St Andrews
St Andrews, Scotland
Contact:
Fiona Armstrong, Press Officer
01334 462530 / 462529
Julia Maddock
STFC Press Office
+44 1793 442094 / +44 7901 514 975
Thursday 15 May 2008
Universe shines twice as bright
The Universe is actually twice as bright than was previously thought,
according to research conducted by an international team of astronomers.
Dr Simon Driver from the University of St Andrews has discovered dust is
obscuring approximately half of the light that the Universe is generating.
Lead author Dr Driver of the School of Physics and Astronomy said, "For
nearly two decades we've argued about whether the light that we see from
distant galaxies tells the whole story or not. It doesn't; in fact only
half the energy produced by stars actually reaches our telescopes
directly, the rest is blocked by dust grains."
While astronomers have known for some time that the Universe contains
small grains of dust, they had not realised the extent to which this is
restricting the amount of light that we can see. The dust absorbs
starlight and re-emits it, making it glow. They knew that existing models
were flawed, because the energy output from glowing dust appeared to be
greater than the total energy produced by the stars.
Dr Driver explained, "You can't get more energy out than you put in so we
knew something was very wrong. Even so, the scale of the dust problem has
come as a shock -- it appears galaxies are generating twice as much
starlight as previously thought!"
The team combined an innovative new model of the dust distribution in
galaxies developed by Dr Cristina Popescu of the University of Central
Lancashire and Prof Richard Tuffs of the Max Plank Institute for Nuclear
Physics, with data from the Millennium Galaxy Catalogue, a
state-of-the-art high resolution catalogue of 10,000 galaxies assembled by
Driver and his team.
Using the new model, the astronomers could calculate precisely the
fraction of starlight blocked by the dust. The key test that the new
model passed was whether the energy of the absorbed starlight equated to
that detected from the glowing dust.
"The equation balanced perfectly," said Dr Cristina Popescu, "and for the
first time we have a total understanding of the energy output of the
Universe over a monumental wavelength range. With the new calibrated
model in hand we can now calculate precisely the fraction of starlight
blocked by the dust."
The Universe is currently generating energy, via nuclear fusion in the
cores of stars, at a whopping rate of 5 quadrillion Watts per cubic light
year -- about 300 times the average energy consumption of the Earth's
population.
"For over 70 years an accurate description of how galaxies, the locations
where matter is churned into energy, form and evolve has eluded us.
Balancing the cosmic energy budget is an important step forward," said Dr
Driver.
After carefully measuring the brightness of thousands of disc-shaped
galaxies with different orientations, the astronomers matched their
observations to computer models of dusty galaxies. From this they were
able to calibrate the models and, for the first time, determine how much
light is obscured when a galaxy has a face-on orientation. This then
allowed them to determine the absolute fraction of light that escapes in
each direction from a galaxy.
Dr Driver explained the discovery that only half of the visible starlight
gets out, while a mere 10 percent of the UV radiation escapes from
galaxies. He said, "When the dust blocks the light, it is effectively
heated and glows like the thermal images seen with military night vision
goggles.
"When we look at galaxies using infrared satellites, we actually see the
warm dust glowing. The amount of energy which the Universe is releasing at
these wavelengths exactly balanced our determination of how much UV and
visible light is absorbed by the dust."
While modern instruments allow astronomers to see further into space, they
can't eliminate the obscuring effect from these tiny dust grains. The
work is set to continue but with a change of focus from the study of the
Universe as a whole, to the study of individual galaxies. This requires
two new facilities which are coming online this year. The first is the
VISTA telescope, which will soon commence operations in Chile and the
second is the Herschel satellite due for launch later in the year.
Dr Driver continued, "We still aren't able to observe the Universe in its
full glory, however we do now better understand the effect that all of
this dust is having on scientific observations."
UK astronomers enjoy full access to both of these facilities through the
UK's membership, paid by the Science and Technology Facilities Council, of
the European Southern Observatory and the European Space Agency which are
responsible for operating these facilities.
The research is published in the latest Astrophysical Journal Letters
(10th May).
Note to Editors:
Authors: Simon Driver (University of St Andrews, Scotland), Cristina
Popescu (University of Central Lancashire, England), Richard Tuffs
(Max-Planck Institute fur Nuclear Physics, Germany), Alister Graham
(Swinburne University of Technology, Australia), Jochen Liske (European
Southern Observatory, Germany), Ivan Baldry (Liverpool John Moores
University, England).
This research has been funded by the Science and Technology Facilities
Council (STFC), the Australian Research Council, the Max-Planck Society
and a Livesey award from the University of Central Lancashire.
The Millennium Galaxy Catalogue consists of data from the Anglo-Australian
Telescope, The Australian National University's 2.3 m telescope at Siding
Spring Observatory, the Isaac Newton Telescope and the Telescopio
Nazionale Galileo at the Spanish Observatorio del Roque de Los Muchachos,
La Palma, of the Instituto de Astrofisica de Canarias, and also from the
Gemini and ESO New Technology Telescopes in Chile.
The researchers are available for interview:
Dr Simon Driver
University of St Andrew
01334-461680/ 07919305906
Dr Cristina Popescu
University of Central Lancashire
01772 893 551
Dr Ivan Baldry
Liverpool John Moores University
ikb @ astro.livjm.ac.uk
Dr Richard Tuffs
Max Plank Institute for Nuclear Physics
Richard.Tuffs @ mpi-hd.mpg.de
Dr Alister Graham
Swinburne University of Technology
Tel: +61 3 9214 8784
Dr Jochen Liske
ESO
Tel: +49 89 32006582
Note to Picture Editors:
High resolution images showing galaxies known to contain dust obscuring
the stars are available from
http://astronomy.swin.edu.au/~agraham/dust/dust.html
Yousuf Khan
> Universe shines twice as bright
>
> The Universe is actually twice as bright than was previously thought,
> according to research conducted by an international team of astronomers.
>
> Dr Simon Driver from the University of St Andrews has discovered dust is
> obscuring approximately half of the light that the Universe is generating.
>
> Lead author Dr Driver of the School of Physics and Astronomy said, "For
> nearly two decades we've argued about whether the light that we see from
> distant galaxies tells the whole story or not. It doesn't; in fact only
> half the energy produced by stars actually reaches our telescopes
> directly, the rest is blocked by dust grains."
>
> While astronomers have known for some time that the Universe contains
> small grains of dust, they had not realised the extent to which this is
> restricting the amount of light that we can see. The dust absorbs
> starlight and re-emits it, making it glow. They knew that existing models
> were flawed, because the energy output from glowing dust appeared to be
> greater than the total energy produced by the stars.
Will the recalculation of the brightness magnitudes that this discovery
will require, mean that the galaxies are closer than they look?
Yousuf Khan
Hannu Poropudas
> Press Office
> University of St Andrews
> St Andrews, Scotland
>
> Contact:
> Fiona Armstrong, Press Officer
> 01334 462530 / 462529
>
> Julia Maddock
> STFC Press Office
> +44 1793 442094 / +44 7901 514 975
>
> Thursday 15 May 2008
>
> Universe shines twice as bright
>
> The Universe is actually twice as bright than was previously thought,
> according to research conducted by an international team of astronomers.
...
The Universe is currently generating energy, via nuclear fusion in the
cores of stars, at a whopping rate of 5 quadrillion Watts per cubic
light
year -- about 300 times the average energy consumption of the Earth's
population.
...
5 * 10^24 W/(lightyear)^3
Does this give any mass estimations of the Universe, if we
think the Universe as a sphere of radius 13.8 * 10^9 light years ?
Hannu
Steve Willner
Yousuf Khan <bbb...@yahoo.com> writes:
> Will the recalculation of the brightness magnitudes that this discovery
> will require, mean that the galaxies are closer than they look?
I doubt it. Observations of both Cepheids and supernovae -- the
principal distance indicators -- are already corrected for reddening
to each individual star observed. The new result is for the
integrated light of entire galaxies; in effect, our observations
don't see half the stars.
What _may_ change is estimates of the stellar mass of galaxies and of
the age of their stellar populations. However, estimates of stellar
mass from infrared light shouldn't change much if at all. I haven't
looked into the issue enough to know whether other estimates really
will change or not. The reddening may already be fully taken into
account in existing calculations. It's not as though nobody knew
reddening existed!
--
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.)
Hannu Poropudas
> In article <482e6f7...@news.bnb-lp.com>,
> Yousuf Khan <bbb...@yahoo.com> writes:
>
> > Will the recalculation of the brightness magnitudes that this discovery
> > will require, mean that the galaxies are closer than they look?
>
> I doubt it. Observations of both Cepheids and supernovae -- the
> principal distance indicators -- are already corrected for reddening
> to each individual star observed. The new result is for the
> integrated light of entire galaxies; in effect, our observations
> don't see half the stars.
>
> What _may_ change is estimates of the stellar mass of galaxies and of
> the age of their stellar populations. However, estimates of stellar
> mass from infrared light shouldn't change much if at all. I haven't
> looked into the issue enough to know whether other estimates really
> will change or not. The reddening may already be fully taken into
> account in existing calculations. It's not as though nobody knew
> reddening existed!
>
> --
> 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.)
...
The Universe is currently generating energy, via nuclear fusion in the
cores of stars, at a whopping rate of 5 quadrillion Watts per cubic
light
year -- about 300 times the average energy consumption of the Earth's
population.
...
5 * 10^24 W/(lightyear)^3
Does this give any mass estimations of the present space, if we
think the present space as a sphere of radius 13.8 * 10^9 light
years ?
Does this give any mass estimations of the Universe, if
we think the Universe as a pseudo-sphere of radius 13.8 * 10^9 light
years
(In this picture the slice of this pseudo-sphere is a couple of
circles at
present time, if one space dimension is shrunken away from 3+1 space-
time
dimensions in this picture for more easy to comprehed the full 3+1-
dimensional
model. The time-axis is symmetry axis of this pseudo-sphere. Two-
orthogonal axis
are two space axis. At certain point of time one circle represents
contracting space
and one expanding space. In this picture there exist hundreds of
thousands of such
couples from the big bang start to present time. At present we are
allowed to move
only inside the expanding circle which corresponds to the present
space.) ???
Maybe this is impossible to estimate if mass is definded to be only
due
expansion or contraction resistance of the Universe???
Hannu
Yousuf Khan
> In article <482e6f72$1...@news.bnb-lp.com>,
> Yousuf Khan <bbb...@yahoo.com> writes:
>> Will the recalculation of the brightness magnitudes that this discovery
>> will require, mean that the galaxies are closer than they look?
>
> I doubt it. Observations of both Cepheids and supernovae -- the
> principal distance indicators -- are already corrected for reddening
> to each individual star observed. The new result is for the
> integrated light of entire galaxies; in effect, our observations
> don't see half the stars.
>
> What _may_ change is estimates of the stellar mass of galaxies and of
> the age of their stellar populations. However, estimates of stellar
> mass from infrared light shouldn't change much if at all. I haven't
> looked into the issue enough to know whether other estimates really
> will change or not. The reddening may already be fully taken into
> account in existing calculations. It's not as though nobody knew
> reddening existed!
If infrared images are just the "glow" of the dust inside the galaxies,
then dust is pretty widely scattered throughout a galaxy, so wouldn't it
make it look like there are *more* stars than other wavelength images
would look like? What I'm trying to get at here is that if optical
wavelength images are blurred by the dust, and make it look like there
are less stars, and infrared makes it look like there are more stars,
then is the stellar mass somewhere down the middle?
Yousuf Khan
Steve Willner
Yousuf Khan <bbb...@yahoo.com> writes:
> If infrared images are just the "glow" of the dust inside the galaxies,
Sorry, I should have been a bit more careful to specify wavelengths.
Infrared stellar mass estimates generally come from (rest)
wavelengths between 1.5 and 3.6 microns or so. These wavelengths are
near the peak of stellar emission for normal stellar populations and
are relatively unaffected by interstellar reddening and also by dust
emission. They are also less affected by the age of a stellar
population than visible light.
> then dust is pretty widely scattered throughout a galaxy, so wouldn't it
> make it look like there are *more* stars than other wavelength images
If you want to see the dust in emission, you generally have to look
at wavelengths longer than 3 microns or so. The dust distribution is
generally very clumpy, but at least for spiral galaxies, dust is
ubiquitous throughout the galaxy.
If someone were to misinterpret dust emission as starlight, then yes,
that would lead to an overestimate of the stellar mass. Generally,
though, it's pretty easy to choose a wavelength where essentially all
the emission is from stars. As you might guess from the overlap in
the wavelength ranges I've quoted, there may be problems telling
what's what around 3 microns in very dusty galaxies.
> What I'm trying to get at here is that if optical
> wavelength images are blurred by the dust,
They aren't blurred. Some of the light that "should" get through is
missing. Blue light is affected more strongly than red, hence the
term "reddening." But nothing is blurred.
Yousuf Khan
> Infrared stellar mass estimates generally come from (rest)
> wavelengths between 1.5 and 3.6 microns or so. These wavelengths are
> near the peak of stellar emission for normal stellar populations and
> are relatively unaffected by interstellar reddening and also by dust
> emission. They are also less affected by the age of a stellar
> population than visible light.
>
>> then dust is pretty widely scattered throughout a galaxy, so wouldn't it
>> make it look like there are *more* stars than other wavelength images
>
> If you want to see the dust in emission, you generally have to look
> at wavelengths longer than 3 microns or so. The dust distribution is
> generally very clumpy, but at least for spiral galaxies, dust is
> ubiquitous throughout the galaxy.
>
> If someone were to misinterpret dust emission as starlight, then yes,
> that would lead to an overestimate of the stellar mass. Generally,
> though, it's pretty easy to choose a wavelength where essentially all
> the emission is from stars. As you might guess from the overlap in
> the wavelength ranges I've quoted, there may be problems telling
> what's what around 3 microns in very dusty galaxies.
I understand, so we're a little "foggy" (pun intended) about what is
stars and what is dust in the 3 to 3.6 mm wavelength. What are the most
common infrared wavelengths that are studied, would they perchance be in
this range?
Yousuf Khan
Steve Willner
Yousuf Khan <bbb...@yahoo.com> writes:
> I understand, so we're a little "foggy" (pun intended) about what is
> stars and what is dust in the 3 to 3.6 mm wavelength.
That's microns or micro-meters, not millimeters. Separating stars
from dust is really only a problem in very dusty galaxies and
galaxies with active nuclei. For normal galaxies such as the Milky
Way, 3.6 microns is pretty much stars with perhaps a few percent dust
contribution.
> What are the most common infrared wavelengths that are studied,
> would they perchance be in this range?
"Infrared" encompasses a wide range of wavelengths. The I and Z
wavelengths (0.76 and 0.91 microns respectively for SDSS, a bit
different for other filter sets) can't be seen by human eyes, but
they are usually included in "visible" because they use the same
silicon technology as shorter wavelengths.
Beyond 1 micron, detector technology changes, so this is a good
practical limit of "infrared." To observe from the ground, you have
to pick wavelengths where atmospheric transmission is good. Common
values are 1.25, 1.65, 2.2, 3.5, 5, 10, and 20 microns. The 2MASS
all-sky survey observed at the shortest three of these. Beyond
20 microns, the atmosphere is pretty opaque until you get to
350 microns, which might be called "submillimeter" instead of
"infrared." The 350-micron window is pretty rotten, though, and it
can only be used at high, dry sites. Even at Mauna Kea, most nights
are poor for this wavelength. Another "window," even worse than 350,
is at 450 microns. The atmosphere starts to get better around
800 microns, but then you are beyond what most people consider
"infrared."
From space, you can observe at any wavelength you want, and different
missions have made different choices. The shortest wavelength for
the Spitzer Space Telescope, for example, is 3.6 microns, and the
longest is 160 microns. At these wavelengths, sensitivities from
space are vastly better than from the ground because telescopes can
be cooled.