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Jun 12, 2022, 3:26:43â€¯PM6/12/22

to

In this article https://www.nature.com/articles/d41586-022-01320-y we can read:

"The long-awaited results, show an image etc. : a ring of radiation

surrounds a darker disk of precisely the size that was predicted from

indirect observations and from GR."

My question is: If you travel in a spaceship around this BH, like the

Sun travels around this BH, will you always observe more or less the

same ring? The same question in opposite direction?

My prediction is: Yes.

Nicolaas Vroom

https://www.nicvroom.be/

"The long-awaited results, show an image etc. : a ring of radiation

surrounds a darker disk of precisely the size that was predicted from

indirect observations and from GR."

My question is: If you travel in a spaceship around this BH, like the

Sun travels around this BH, will you always observe more or less the

same ring? The same question in opposite direction?

My prediction is: Yes.

Nicolaas Vroom

https://www.nicvroom.be/

Jun 24, 2022, 6:07:34â€¯AM6/24/22

to

Op zondag 12 juni 2022 om 21:26:43 UTC+2 schreef Nicolaas Vroom:

> My prediction is: Yes.

What that means that the BH is a spherical symmetrical object and that

there exists a 'gaseous' layer outside the radius of the BH which emits

light in all? directions. From the point of view of our earth we observe

this gaseous layer as a ring, but this view will be the same for every

observer, at the same distance as us, from the BH. In reality such a

physical ring, perpendicular to our line of sight, does not exist; its a

physical layer.

Nicolaas Vroom

https://www.nicvroom.be/

[Moderator's note: Almost all, or all, astrophysical black holes are not

spherically symmetric in the sense that they rotate. Rotating black

holes are more complicated. What an observer actually sees when looking

at a black hole is not trivial to calculate. In any case, the general

consensus is that black holes detectable via radiation emitted from near

them have an accretion disk and thus aren't spherically symmetric.

-P.H.]

> My prediction is: Yes.

What that means that the BH is a spherical symmetrical object and that

there exists a 'gaseous' layer outside the radius of the BH which emits

light in all? directions. From the point of view of our earth we observe

this gaseous layer as a ring, but this view will be the same for every

observer, at the same distance as us, from the BH. In reality such a

physical ring, perpendicular to our line of sight, does not exist; its a

physical layer.

Nicolaas Vroom

https://www.nicvroom.be/

[Moderator's note: Almost all, or all, astrophysical black holes are not

spherically symmetric in the sense that they rotate. Rotating black

holes are more complicated. What an observer actually sees when looking

at a black hole is not trivial to calculate. In any case, the general

consensus is that black holes detectable via radiation emitted from near

them have an accretion disk and thus aren't spherically symmetric.

-P.H.]

Jun 28, 2022, 3:28:39â€¯AM6/28/22

to

Op vrijdag 24 juni 2022 om 12:07:34 UTC+2 schreef Nicolaas Vroom:

> What that means that the BH is a spherical symmetrical object and that

> there exists a 'gaseous' layer outside the radius of the BH which emits

> light in all? directions.

SNIP

> [Moderator's note: Almost all, or all, astrophysical black holes are not

> spherically symmetric in the sense that they rotate.

My understanding is that also all stars and planets rotate, at the same

time many of these could be called spherical symmetric like our earth

and the Sun.

> Rotating black holes are more complicated. What an observer actually

> sees when looking at a black hole is not trivial to calculate.

The first step is to observe. To calculate is a second step.

> In any case, the general

> consensus is that black holes detectable via radiation emitted from near

> them have an accretion disk and thus aren't spherically symmetric.

The question is to what extend can we conclude, based on observations,

that the BH, part of Sagittarius A*, has an accretion disk. Observing

the picture in https://www.nature.com/articles/d41586-022-01320-y the

ring surrounding the BH must be an 'indication' of this disk. If that is

the case the ring must be situated in a plane almost perpendicular

towards the direction of the line of sight between the earth and the

centre of the BH. (1) This direction must also be the same as the axis

of rotation of the BH.

Assuming that the ring is part of an accretion disk, I should expect,

that if we travel around this BH, like the Sun does around the BH, the

shape of this ring, as observed from our spaceship, must also change.

This shape must be almost the same after we have travelled 180 degrees

and the same after 360 degrees.

As I mentioned before, I have my doubts. The ring does not change and

there is no prove of an accretion disk, based on this image.

What also is in favour of a sperical object is that the movement of the

stars around the BH is random. There is no preference.

I found also a different article:

https://www.nasa.gov/feature/goddard/2021/hubble-mini-jet-found-near-milky-ways-supermassive-black-hole

This article also shows the direction of rotation of the BH.

The direction is different compared with (1) above.

My impression is that when you read this article and other articles the

accretion disks are of temporary nature and depend about source, that

causes the inflow of material. Together the BH and the source can be

considered as a binary system.

As mentioned above the movement of the stars around Sagitarrius A* are

random, as such, my guess is, that the direction of possible accretion

disks is also random, which is in contradiction with observation (1)

Nicolaas Vroom

https://www.nicvroom.be

[[Mod. note -- A few comments:

1. The Earth is *approximately* spherically symmetric, but if you look

more closely it's shape is in fact rotationally flattened. That is,

the Earth's equatorial radius is about 0.34% larger than its polar

radius, so the Earth is in fact NOT spherically symmetric.

2. While it's true that if we travel around the Sgr A* BH, its apparent

shape will change, that doesn't help us right now: our solar system

takes around 250 million years to orbit the center of our galaxy,

so we're not going to get to look at the Sgr A* BH from a

significantly different orientation any time in our lives.

3. Accretion disks (including the one around the Sgr A* BH) are indeed

temporary and depend on the availablity of source matter. But I

wouldn't say that the BH and the source are a "binary" system, because

there's no reason to think that the source is a single compact object.

Rather, the BH is embedded in a cloud of (moving) stars and

interstellar gas.

4. This 2020 article by Fragione & Loeb,

https://iopscience.iop.org/article/10.3847/2041-8213/abb9b4

(which argues for a relatively low (slow) spin for the Sgr A* BH)

notes that past studies have given conflicting values for that spin.

I don't know enough about this subject to have an informed opionion

myself. Given the instruments now operational, we should know a

*lot* more about this in a few years, especially once ESO's

Extremely Large Telescope is operational (planned for 2027ish).

-- jt]]

> What that means that the BH is a spherical symmetrical object and that

> there exists a 'gaseous' layer outside the radius of the BH which emits

> light in all? directions.

> [Moderator's note: Almost all, or all, astrophysical black holes are not

> spherically symmetric in the sense that they rotate.

time many of these could be called spherical symmetric like our earth

and the Sun.

> Rotating black holes are more complicated. What an observer actually

> sees when looking at a black hole is not trivial to calculate.

> In any case, the general

> consensus is that black holes detectable via radiation emitted from near

> them have an accretion disk and thus aren't spherically symmetric.

that the BH, part of Sagittarius A*, has an accretion disk. Observing

the picture in https://www.nature.com/articles/d41586-022-01320-y the

ring surrounding the BH must be an 'indication' of this disk. If that is

the case the ring must be situated in a plane almost perpendicular

towards the direction of the line of sight between the earth and the

centre of the BH. (1) This direction must also be the same as the axis

of rotation of the BH.

Assuming that the ring is part of an accretion disk, I should expect,

that if we travel around this BH, like the Sun does around the BH, the

shape of this ring, as observed from our spaceship, must also change.

This shape must be almost the same after we have travelled 180 degrees

and the same after 360 degrees.

As I mentioned before, I have my doubts. The ring does not change and

there is no prove of an accretion disk, based on this image.

What also is in favour of a sperical object is that the movement of the

stars around the BH is random. There is no preference.

I found also a different article:

https://www.nasa.gov/feature/goddard/2021/hubble-mini-jet-found-near-milky-ways-supermassive-black-hole

This article also shows the direction of rotation of the BH.

The direction is different compared with (1) above.

My impression is that when you read this article and other articles the

accretion disks are of temporary nature and depend about source, that

causes the inflow of material. Together the BH and the source can be

considered as a binary system.

As mentioned above the movement of the stars around Sagitarrius A* are

random, as such, my guess is, that the direction of possible accretion

disks is also random, which is in contradiction with observation (1)

Nicolaas Vroom

https://www.nicvroom.be

[[Mod. note -- A few comments:

1. The Earth is *approximately* spherically symmetric, but if you look

more closely it's shape is in fact rotationally flattened. That is,

the Earth's equatorial radius is about 0.34% larger than its polar

radius, so the Earth is in fact NOT spherically symmetric.

2. While it's true that if we travel around the Sgr A* BH, its apparent

shape will change, that doesn't help us right now: our solar system

takes around 250 million years to orbit the center of our galaxy,

so we're not going to get to look at the Sgr A* BH from a

significantly different orientation any time in our lives.

3. Accretion disks (including the one around the Sgr A* BH) are indeed

temporary and depend on the availablity of source matter. But I

wouldn't say that the BH and the source are a "binary" system, because

there's no reason to think that the source is a single compact object.

Rather, the BH is embedded in a cloud of (moving) stars and

interstellar gas.

4. This 2020 article by Fragione & Loeb,

https://iopscience.iop.org/article/10.3847/2041-8213/abb9b4

(which argues for a relatively low (slow) spin for the Sgr A* BH)

notes that past studies have given conflicting values for that spin.

I don't know enough about this subject to have an informed opionion

myself. Given the instruments now operational, we should know a

*lot* more about this in a few years, especially once ESO's

Extremely Large Telescope is operational (planned for 2027ish).

-- jt]]

Jul 7, 2022, 2:11:24â€¯AM7/7/22

to

On 28/06/2022 08:28, Nicolaas Vroom wrote:

> Op vrijdag 24 juni 2022 om 12:07:34 UTC+2 schreef Nicolaas Vroom:

>

>> What that means that the BH is a spherical symmetrical object and that

>> there exists a 'gaseous' layer outside the radius of the BH which emits

>> light in all? directions.

>

> SNIP

>

>> [Moderator's note: Almost all, or all, astrophysical black holes are not

>> spherically symmetric in the sense that they rotate.

>

> My understanding is that also all stars and planets rotate, at the same

> time many of these could be called spherical symmetric like our earth

> and the Sun.

Apart from having a spin axis... They are oblate spheroids for the most
> Op vrijdag 24 juni 2022 om 12:07:34 UTC+2 schreef Nicolaas Vroom:

>

>> What that means that the BH is a spherical symmetrical object and that

>> there exists a 'gaseous' layer outside the radius of the BH which emits

>> light in all? directions.

>

> SNIP

>

>> [Moderator's note: Almost all, or all, astrophysical black holes are not

>> spherically symmetric in the sense that they rotate.

>

> My understanding is that also all stars and planets rotate, at the same

> time many of these could be called spherical symmetric like our earth

> and the Sun.

part and become more so the faster that they are spinning.

In our own solar system Saturn and Uranus both have equatorial rings -

the former being its most spectacular feature.

>

>> Rotating black holes are more complicated. What an observer actually

>> sees when looking at a black hole is not trivial to calculate.

>

> The first step is to observe. To calculate is a second step.

We can observe directly a close analogue of a spinning black hole in the
>> Rotating black holes are more complicated. What an observer actually

>> sees when looking at a black hole is not trivial to calculate.

>

> The first step is to observe. To calculate is a second step.

Crab nebula pulsar and with enough resolution in X-rays to see both the

accretion disk and jets coming from the poles. Neutron stars are only a

relatively modest factor of about 3 short of being black holes. Drop

enough extra mass onto them from a nearby star and they may become one.

https://chandra.harvard.edu/photo/2017/crab/

Select X-ray

Chandra has also imaged Sgr A* and that puts bounds on how much matter

in its vicinity actually goes down the plug hole (~1% at most).

https://chandra.harvard.edu/photo/2013/sgra_gas/

This URL may help answer most of the OPs questions:

https://www.space.com/sagittarius-a

>> In any case, the general

>> consensus is that black holes detectable via radiation emitted from near

>> them have an accretion disk and thus aren't spherically symmetric.

>

> The question is to what extend can we conclude, based on observations,

> that the BH, part of Sagittarius A*, has an accretion disk. Observing

> the picture in https://www.nature.com/articles/d41586-022-01320-y the

> ring surrounding the BH must be an 'indication' of this disk. If that is

> the case the ring must be situated in a plane almost perpendicular

> towards the direction of the line of sight between the earth and the

> centre of the BH. (1) This direction must also be the same as the axis

> of rotation of the BH.

of some sort if there is any matter near enough to be subject to being

pulled in. It has to lose angular momentum somehow to fall into it.

The black hole has strong enough gravity to bend light paths over the

poles so that you see something that is quite distorted from whatever

angle you look. Raytracers have simulated this. I am surprised how close

to a blurred version of their predictions the observations have been!

Sera Markoff's page has a nice movie of how the appearance of the (M87

BH) would change with observing wavelength.

https://www.seramarkoff.com/2022/02/exploring-the-appearance-of-black-hole-by-ray-tracing/

I am more concerned with the dynamical timescales making the intrinsic

assumptions of aperture synthesis invalid for Sgr A*. I know they imaged

it in snapshot mode to try and avoid these issues. ISTR the images

obtained clustered around certain specific patterns of brightness.

A few are shown in Fig 3 here. I'm sure there is a larger set somewhere.

https://iopscience.iop.org/article/10.3847/2041-8213/ac6674/pdf

> Assuming that the ring is part of an accretion disk, I should expect,

> that if we travel around this BH, like the Sun does around the BH, the

> shape of this ring, as observed from our spaceship, must also change.

> This shape must be almost the same after we have travelled 180 degrees

> and the same after 360 degrees.

accretion disk may change on timescales worryingly close to the time

required to obtain enough data for a satisfactory image of the target.

By comparison the core of M87 is about a thousand times bigger and also

a thousand times further away so although about the same apparent size

on the sky viewed from Earth is much more stable in its appearance.

> As I mentioned before, I have my doubts. The ring does not change and

> there is no prove of an accretion disk, based on this image.

>

> What also is in favour of a sperical object is that the movement of the

> stars around the BH is random. There is no preference.

mass as far as its gravitational dynamics are concerned. A small amount

of frame dragging could be detectable but that becomes a much more

significant effect when they are closest. Has any dynamical evidence of

frame dragging been seen on any stars making very close approaches?

(my guess is we don't have the resolution to be able to tell)

It would be fun to see what happens if a star does get too close and is

shredded and the whole thing lights up brightly for a while.

> I found also a different article:

> https://www.nasa.gov/feature/goddard/2021/hubble-mini-jet-found-near-milky-ways-supermassive-black-hole

> This article also shows the direction of rotation of the BH.

> The direction is different compared with (1) above.

>

> My impression is that when you read this article and other articles the

> accretion disks are of temporary nature and depend about source, that

> causes the inflow of material. Together the BH and the source can be

> considered as a binary system.

>

> As mentioned above the movement of the stars around Sagitarrius A* are

> random, as such, my guess is, that the direction of possible accretion

> disks is also random, which is in contradiction with observation (1)

angle it will fairly quickly be spread out along its orbit and then

settle down into an equatorial ring or donut due to friction. The spin

of a black hole causes strong frame dragging in close proximity to it.

Also quite likely to have a ferocious magnetic field as well.

--

Regards,

Martin Brown

Jul 10, 2022, 1:11:39â€¯AM7/10/22

to

Op dinsdag 28 juni 2022 om 09:28:39 UTC+2 schreef Nicolaas Vroom:

> [[Mod. note -- A few comments:

> 1. The Earth is *approximately* spherically symmetric, but if you look

> more closely its shape is in fact rotationally flattened. That is,

to prove, based on observational evidence.

> 2. While it's true that if we travel around the Sgr A* BH, its apparent

> shape will change, that doesn't help us right now: our solar system

> takes around 250 million years to orbit the centre of our galaxy,

a picture as shown in https://www.nature.com/articles/d41586-022-01320-y.

My expectation that the 80 pictures will be almost the same.

A different way to travel around the BH is in the same plane as the picture,

as observed ring, at the same distance as we are at the present.

My expectation that these 80 pictures also will be almost the same.

Two options: A ring or a vertical thick line. I expect a ring.

That means the ring around the dark circle in the centre is not a physical

ring but an image of the light, originating from the surroundings around

the BH, travelling in our directions.

The most probably explanation, if the pictures are almost the same,

that the surroundings of the BH are 'spherical' the same.

The consequence is that this is not an image of a BH. But this is open

for discussion. (That does not mean there is no BH)

If it was a physical ring the pictures should not be the same.

A picture of the BH M87 also shows a ring.

> 3. Accretion disks (including the one around the Sgr A* BH) are indeed

> temporary and depend on the availability of source matter. But I

if you compare S62 with for example S6. The results of

my simulations show that the gravitational field of S6 influences

the behaviour of S62. S62 is a star which revolves in about 10 years

around Sgr A* BH while S6 does this in about 192 years. This variable

gravitational field is visible in the form of a gravitational wave.

Select this link:

https://www.nicvroom.be/VB2019%20Sagittarius.program.htm#par%206.6

> 4. This 2020 article by Fragione & Loeb,

> https://iopscience.iop.org/article/10.3847/2041-8213/abb9b4

> (which argues for a relatively low (slow) spin for the Sgr A* BH)

> notes that past studies have given conflicting values for that spin.

> I don't know enough about this subject to have an informed opinion

"X-ray astronomy comes of age"

https://www.nature.com/articles/s41586-022-04481-y

Here we can read at page 265:

Sgr A*, the SuperMassiveBH in the centre of the Milky Way is currently

in a radiatively inefficient accretion phase.... Less than 1% of this

gas accretes onto the SMBH, the remainder being ejected in a polar outflow...

The number of bright flares seen by Chandra and XMM-Newton increased about

six months after the closest approach of the gas cloud G2 to Sgr A*, which

suggests that its passage triggered additional accretion.

Nicolaas Vroom

http://www.nicvroom.be/

> Op vrijdag 24 juni 2022 om 12:07:34 UTC+2 schreef Nicolaas Vroom:

SNIP
> [[Mod. note -- A few comments:

> 1. The Earth is *approximately* spherically symmetric, but if you look

> the Earth's equatorial radius is about 0.34% larger than its polar

> radius, so the Earth is in fact NOT spherically symmetric.

I expect the 'same' can be said of the Sgr A* BH, but very difficult
> radius, so the Earth is in fact NOT spherically symmetric.

to prove, based on observational evidence.

> 2. While it's true that if we travel around the Sgr A* BH, its apparent

> shape will change, that doesn't help us right now: our solar system

> so we're not going to get to look at the Sgr A* BH from a

> significantly different orientation any time in our lives.

My idea is to travel more in 80 days around the Sgr A* BH and make each day
> significantly different orientation any time in our lives.

a picture as shown in https://www.nature.com/articles/d41586-022-01320-y.

My expectation that the 80 pictures will be almost the same.

A different way to travel around the BH is in the same plane as the picture,

as observed ring, at the same distance as we are at the present.

My expectation that these 80 pictures also will be almost the same.

Two options: A ring or a vertical thick line. I expect a ring.

That means the ring around the dark circle in the centre is not a physical

ring but an image of the light, originating from the surroundings around

the BH, travelling in our directions.

The most probably explanation, if the pictures are almost the same,

that the surroundings of the BH are 'spherical' the same.

The consequence is that this is not an image of a BH. But this is open

for discussion. (That does not mean there is no BH)

If it was a physical ring the pictures should not be the same.

A picture of the BH M87 also shows a ring.

> 3. Accretion disks (including the one around the Sgr A* BH) are indeed

> wouldn't say that the BH and the source are a "binary" system, because

> there's no reason to think that the source is a single compact object.

> Rather, the BH is embedded in a cloud of (moving) stars and

> interstellar gas.

I agree with you. My main reason, why I'm interested in s-stars, starts
> there's no reason to think that the source is a single compact object.

> Rather, the BH is embedded in a cloud of (moving) stars and

> interstellar gas.

if you compare S62 with for example S6. The results of

my simulations show that the gravitational field of S6 influences

the behaviour of S62. S62 is a star which revolves in about 10 years

around Sgr A* BH while S6 does this in about 192 years. This variable

gravitational field is visible in the form of a gravitational wave.

Select this link:

https://www.nicvroom.be/VB2019%20Sagittarius.program.htm#par%206.6

> 4. This 2020 article by Fragione & Loeb,

> https://iopscience.iop.org/article/10.3847/2041-8213/abb9b4

> (which argues for a relatively low (slow) spin for the Sgr A* BH)

> notes that past studies have given conflicting values for that spin.

> myself. Given the instruments now operational, we should know a

> *lot* more about this in a few years, especially once ESO's

> Extremely Large Telescope is operational (planned for 2027ish).

> -- jt]]

A good article to read is regarding this subject is:
> *lot* more about this in a few years, especially once ESO's

> Extremely Large Telescope is operational (planned for 2027ish).

> -- jt]]

"X-ray astronomy comes of age"

https://www.nature.com/articles/s41586-022-04481-y

Here we can read at page 265:

Sgr A*, the SuperMassiveBH in the centre of the Milky Way is currently

in a radiatively inefficient accretion phase.... Less than 1% of this

gas accretes onto the SMBH, the remainder being ejected in a polar outflow...

The number of bright flares seen by Chandra and XMM-Newton increased about

six months after the closest approach of the gas cloud G2 to Sgr A*, which

suggests that its passage triggered additional accretion.

Nicolaas Vroom

http://www.nicvroom.be/

Jul 10, 2022, 1:16:35â€¯AM7/10/22

to

Op donderdag 7 juli 2022 om 08:11:24 UTC+2 schreef Martin Brown:

the light we see is more or less emitted in our direction.

[[Mod. note -- You're mistaken. The light we is is that which

*eventually* is pointing in our direction, but it may have been

emitted in a very different direction (and then had its path bent by

the strong gravitational field into one pointing in our direction).

-- jt]]

> The black hole has strong enough gravity to bend light paths over the

> poles so that you see something that is quite distorted from whatever

> angle you look. Raytracers have simulated this. I am surprised how close

> to a blurred version of their predictions the observations have been!

That is correct.

But this light can come from all directions and also be emitted in all

directions. Part of that emitted light can come in our direction.

> > Assuming that the ring is part of an accretion disk, I should expect,

> > that if we travel around this BH, like the Sun does around the BH, the

> > shape of this ring, as observed from our spaceship, must also change.

> > This shape must be almost the same after we have travelled 180 degrees

> > and the same after 360 degrees.

> Not if the thing is interacting with matter. Bright spots on the

> accretion disk may change on timescales worryingly close to the time

> required to obtain enough data for a satisfactory image of the target.

My assumption is that this accretion disc is more or less fixed to the

BH and lies in the plane of the picture. That means if you travel in 80 days

around this BH that when you return after 80 days the picture should

be more or less the same. But the intermediate pictures should not.

If you start from a circle after 10 days this should be an ellipse after

20 days a vertical beam, after 30 days an ellipse and after 40 days again

a circle. What I mean is that to observe a circle is rare.

At the same time, that is my guess, if the BH would be surrounded, with

a more or less equally distributed layer of some gaseous material, it

is possible that you always observe this more or less doughnut shaped

visible ring.

Regards

Nicolaas Vroom.

> On 28/06/2022 08:28, Nicolaas Vroom wrote:

> > The question is to what extend can we conclude, based on observations,

> > that the BH, part of Sagittarius A*, has an accretion disk. Observing

> > the picture in https://www.nature.com/articles/d41586-022-01320-y the

> > ring surrounding the BH must be an 'indication' of this disk. If that is

> > the case the ring must be situated in a plane almost perpendicular

> > towards the direction of the line of sight between the earth and the

> > centre of the BH. (1) This direction must also be the same as the axis

> > of rotation of the BH.

> It would be incredibly surprising if it did not have an accretion disk

> of some sort if there is any matter near enough to be subject to being

> pulled in. It has to lose angular momentum somehow to fall into it.

But during that process light can be emitted in all directions and
> > The question is to what extend can we conclude, based on observations,

> > that the BH, part of Sagittarius A*, has an accretion disk. Observing

> > the picture in https://www.nature.com/articles/d41586-022-01320-y the

> > ring surrounding the BH must be an 'indication' of this disk. If that is

> > the case the ring must be situated in a plane almost perpendicular

> > towards the direction of the line of sight between the earth and the

> > centre of the BH. (1) This direction must also be the same as the axis

> > of rotation of the BH.

> It would be incredibly surprising if it did not have an accretion disk

> of some sort if there is any matter near enough to be subject to being

> pulled in. It has to lose angular momentum somehow to fall into it.

the light we see is more or less emitted in our direction.

[[Mod. note -- You're mistaken. The light we is is that which

*eventually* is pointing in our direction, but it may have been

emitted in a very different direction (and then had its path bent by

the strong gravitational field into one pointing in our direction).

-- jt]]

> The black hole has strong enough gravity to bend light paths over the

> poles so that you see something that is quite distorted from whatever

> angle you look. Raytracers have simulated this. I am surprised how close

> to a blurred version of their predictions the observations have been!

But this light can come from all directions and also be emitted in all

directions. Part of that emitted light can come in our direction.

> > Assuming that the ring is part of an accretion disk, I should expect,

> > that if we travel around this BH, like the Sun does around the BH, the

> > shape of this ring, as observed from our spaceship, must also change.

> > This shape must be almost the same after we have travelled 180 degrees

> > and the same after 360 degrees.

> Not if the thing is interacting with matter. Bright spots on the

> accretion disk may change on timescales worryingly close to the time

> required to obtain enough data for a satisfactory image of the target.

BH and lies in the plane of the picture. That means if you travel in 80 days

around this BH that when you return after 80 days the picture should

be more or less the same. But the intermediate pictures should not.

If you start from a circle after 10 days this should be an ellipse after

20 days a vertical beam, after 30 days an ellipse and after 40 days again

a circle. What I mean is that to observe a circle is rare.

At the same time, that is my guess, if the BH would be surrounded, with

a more or less equally distributed layer of some gaseous material, it

is possible that you always observe this more or less doughnut shaped

visible ring.

Regards

Nicolaas Vroom.

Jul 10, 2022, 3:37:04â€¯PM7/10/22

to

On Sat, 09 Jul 2022 22:16:32 PDT, Nicolaas Vroom

the null geodesic which connects the light source to us? How do we

define the "straightness" which is *more* in "our direction"?

Mach's Principle gets in here, where it holds that there can be no

space wihout some matter to occupy it, i.e., matter is an inherent

part of any complete spatial manifold. Given that, it's pretty hard

to define something "straighter" than the null geodesic contoured by

the essential matter.

[[Mod. note --

1. That's not really what Mach's principle says. Among other things,

a "complete" spatial manifold (which implies that it doesn't contain

any black holes) may be a vacuum (contain no matter), but still

contain spacetime curvature (nonzero Riemann tensor), e.g.,

gravitational waves and/or geons

https://en.wikipedia.org/wiki/Geon_(physics)

2. There are useful notions of "direction" other than those of null

geodesics. For example,

(a) Kerr spacetime is reflection-symmetric about the equator, and

hence "the equator" is a *physically* defined place (set of events)

in Kerr spacetime (i.e., it's one which can be defined uniquely

regardless of the coordinate system in use). And,

(b) Far from the black hole (the asymptotically-flat region) we

have a well-defined sret of nearly-Minkowskian (flat-spacetime)

coordinates, so it's meaningful to talk about things like the

z coordinate (with respect to the equator of a BH whose spin axis

is vertical) of a light ray which is moving horizontally. We

often call this the light ray's "impact parameter".

Putting these together, we can have a situation like this (forgive

the crude ASCII-art; this is best viewed with a monopitch font)):

-----------------------------------

---------------

------

/

// *****

/ *********

+ *********

*********

*****

Here I've shown a side view of a Kerr black hole (denoted by asterisks),

i.e., the BH's spin axis is vertical. A null geodesic originates on the

equator (z=0) at the left and curves over the BH's north pole, arriving

at r=infinity on the right moving horizontally with some impact parameter

b > 0.

Since this light originates on the equator, and winds up in the

asymptotically-flat region travelling parallel the equator but offset

to a nonzero impact parameter, I it's reasonable to say that the

light's path has been bent by the gravitational field.

-- jt]]

>[[Mod. note -- You're mistaken. The light we is is that which

>*eventually* is pointing in our direction, but it may have been

>emitted in a very different direction (and then had its path bent by

>the strong gravitational field into one pointing in our direction).

>-- jt]]

Is this not a philosophic point? What is more "our direction" than
>*eventually* is pointing in our direction, but it may have been

>emitted in a very different direction (and then had its path bent by

>the strong gravitational field into one pointing in our direction).

>-- jt]]

the null geodesic which connects the light source to us? How do we

define the "straightness" which is *more* in "our direction"?

Mach's Principle gets in here, where it holds that there can be no

space wihout some matter to occupy it, i.e., matter is an inherent

part of any complete spatial manifold. Given that, it's pretty hard

to define something "straighter" than the null geodesic contoured by

the essential matter.

[[Mod. note --

1. That's not really what Mach's principle says. Among other things,

a "complete" spatial manifold (which implies that it doesn't contain

any black holes) may be a vacuum (contain no matter), but still

contain spacetime curvature (nonzero Riemann tensor), e.g.,

gravitational waves and/or geons

https://en.wikipedia.org/wiki/Geon_(physics)

2. There are useful notions of "direction" other than those of null

geodesics. For example,

(a) Kerr spacetime is reflection-symmetric about the equator, and

hence "the equator" is a *physically* defined place (set of events)

in Kerr spacetime (i.e., it's one which can be defined uniquely

regardless of the coordinate system in use). And,

(b) Far from the black hole (the asymptotically-flat region) we

have a well-defined sret of nearly-Minkowskian (flat-spacetime)

coordinates, so it's meaningful to talk about things like the

z coordinate (with respect to the equator of a BH whose spin axis

is vertical) of a light ray which is moving horizontally. We

often call this the light ray's "impact parameter".

Putting these together, we can have a situation like this (forgive

the crude ASCII-art; this is best viewed with a monopitch font)):

-----------------------------------

---------------

------

/

// *****

/ *********

+ *********

*********

*****

Here I've shown a side view of a Kerr black hole (denoted by asterisks),

i.e., the BH's spin axis is vertical. A null geodesic originates on the

equator (z=0) at the left and curves over the BH's north pole, arriving

at r=infinity on the right moving horizontally with some impact parameter

b > 0.

Since this light originates on the equator, and winds up in the

asymptotically-flat region travelling parallel the equator but offset

to a nonzero impact parameter, I it's reasonable to say that the

light's path has been bent by the gravitational field.

-- jt]]

Jul 11, 2022, 2:16:49â€¯PM7/11/22

to

In article <62ca8a6d....@news.aioe.org>, er...@flesch.org (Eric

isotropic models based on General Relativity). They can be empty

(contain no matter) but still have (spatial or spacetime) curvature.

Flesch) writes:

> >[[Mod. note -- You're mistaken. The light we is is that which

> >*eventually* is pointing in our direction, but it may have been

> >emitted in a very different direction (and then had its path bent by

> >the strong gravitational field into one pointing in our direction).

> >-- jt]]

>

> Is this not a philosophic point? What is more "our direction" than

> the null geodesic which connects the light source to us? How do we

> define the "straightness" which is *more* in "our direction"?

>

> Mach's Principle gets in here, where it holds that there can be no

> space wihout some matter to occupy it, i.e., matter is an inherent

> part of any complete spatial manifold. Given that, it's pretty hard

> to define something "straighter" than the null geodesic contoured by

> the essential matter.

>

> [[Mod. note --

> 1. That's not really what Mach's principle says. Among other things,

> a "complete" spatial manifold (which implies that it doesn't contain

> any black holes) may be a vacuum (contain no matter), but still

> contain spacetime curvature (nonzero Riemann tensor), e.g.,

> gravitational waves and/or geons

> https://en.wikipedia.org/wiki/Geon_(physics)

Another example are the Friedmann cosmological models (homogeneous and
> >[[Mod. note -- You're mistaken. The light we is is that which

> >*eventually* is pointing in our direction, but it may have been

> >emitted in a very different direction (and then had its path bent by

> >the strong gravitational field into one pointing in our direction).

> >-- jt]]

>

> Is this not a philosophic point? What is more "our direction" than

> the null geodesic which connects the light source to us? How do we

> define the "straightness" which is *more* in "our direction"?

>

> Mach's Principle gets in here, where it holds that there can be no

> space wihout some matter to occupy it, i.e., matter is an inherent

> part of any complete spatial manifold. Given that, it's pretty hard

> to define something "straighter" than the null geodesic contoured by

> the essential matter.

>

> [[Mod. note --

> 1. That's not really what Mach's principle says. Among other things,

> a "complete" spatial manifold (which implies that it doesn't contain

> any black holes) may be a vacuum (contain no matter), but still

> contain spacetime curvature (nonzero Riemann tensor), e.g.,

> gravitational waves and/or geons

> https://en.wikipedia.org/wiki/Geon_(physics)

isotropic models based on General Relativity). They can be empty

(contain no matter) but still have (spatial or spacetime) curvature.

Jul 11, 2022, 2:20:17â€¯PM7/11/22

to

On 10/07/2022 06:16, Nicolaas Vroom wrote:

> Op donderdag 7 juli 2022 om 08:11:24 UTC+2 schreef Martin Brown:

>> On 28/06/2022 08:28, Nicolaas Vroom wrote:

>

>> The black hole has strong enough gravity to bend light paths over the

>> poles so that you see something that is quite distorted from whatever

>> angle you look. Raytracers have simulated this. I am surprised how close

>> to a blurred version of their predictions the observations have been!

>

> That is correct.

> But this light can come from all directions and also be emitted in all

> directions. Part of that emitted light can come in our direction.

Some (perhaps even quite a lot of) relativistic beaming is likely from
> Op donderdag 7 juli 2022 om 08:11:24 UTC+2 schreef Martin Brown:

>> On 28/06/2022 08:28, Nicolaas Vroom wrote:

>

>> The black hole has strong enough gravity to bend light paths over the

>> poles so that you see something that is quite distorted from whatever

>> angle you look. Raytracers have simulated this. I am surprised how close

>> to a blurred version of their predictions the observations have been!

>

> That is correct.

> But this light can come from all directions and also be emitted in all

> directions. Part of that emitted light can come in our direction.

the hotspots nearest the event horizon. Side of the disk coming towards

us will tend to appear both brighter and blue shifted AOTBE.

[[Mod. note -- I've never seen the anacronym "AOTBE" before, but

$SEARCH_ENGINE informs me it typically means "all other things being equal".

-- jt]]

>>> Assuming that the ring is part of an accretion disk, I should expect,

>>> that if we travel around this BH, like the Sun does around the BH, the

>>> shape of this ring, as observed from our spaceship, must also change.

>>> This shape must be almost the same after we have travelled 180 degrees

>>> and the same after 360 degrees.

>

>> Not if the thing is interacting with matter. Bright spots on the

>> accretion disk may change on timescales worryingly close to the time

>> required to obtain enough data for a satisfactory image of the target.

>

> My assumption is that this accretion disc is more or less fixed to the

> BH and lies in the plane of the picture. That means if you travel in 80 days

to a black hole (or for that matter any other gravitating body).

Every particle is in orbit in its own right. The accretion disk is

suffering insane sheer forces and turbulence in all probability.

[[Mod. note -- I think you meant "shear" forces. -- jt]]

The accretion disk is almost certainly spinning in the same sense as the

black hole and as such the last stable circular orbit is just above the

event horizon and travelling at the speed of light. I'd hazard a guess

that the inner section of the accretion disk is pretty much plasma in

almost circular orbits slowly spiralling in towards oblivion.

> around this BH that when you return after 80 days the picture should

> be more or less the same. But the intermediate pictures should not.

> If you start from a circle after 10 days this should be an ellipse after

> 20 days a vertical beam, after 30 days an ellipse and after 40 days again

> a circle. What I mean is that to observe a circle is rare.

decent observational paper of Sgr A* working at the limits of the VLT:

https://www.aanda.org/articles/aa/full_html/2018/10/aa34294-18/aa34294-18.html#FN1

> At the same time, that is my guess, if the BH would be surrounded, with

> a more or less equally distributed layer of some gaseous material, it

> is possible that you always observe this more or less doughnut shaped

> visible ring.

example like M57 the Ring nebula or various supernova remnants it would

not fit with the physics of this situation in close proximity to a

spinning supermassive black hole.

The environment around a Kerr metric BH is anything but isotropic. It

would be great fun to see it swallow a star or gas cloud and illuminate

itself more fully. I wonder how long we will have to wait for that?

--

Regards,

Martin Brown

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