[Dave Lev (OP)]

What is the radius of the accretion Disc in the Milky Way Galaxy?

[PmbPhy]

Please advice the radius of the accretion Disc in the Milky way.

Wow! What a great question. Unfortunately I'm ignorant on this subject. I could find out by Googling it but you'd be able to do the same thing and have better luck since you know more about exactly what you're looking for than I am. However I'm sure others will be of more help than I.

[Dave Lev (OP)]

Thanks

I couldn't find it in the web.
If you have found something, please let me know.

[jeffreyH]

You could argue that the galaxy itself is the accretion disc. Although that would be a huge stretch. Our central black hole is remarkably quiet. I am not sure if anyone has looked for a disc.

EDIT: This answer may be of interest.
https://www.quora.com/Are-galaxies-merely-the-accretion-disks-of-the-supermassive-black-holes-at-their-centres

[guest45734]

Please advice the radius of the accretion Disc in the Milky way.

The innner radius of the accretion disc would be at the event horizon of the black hole which is governed by the Schwarzschild radius. http://hubblesite.org/explore_astronomy/black_holes/encyc_mod3_q3.html
How you define the outer edge of the disc is, as indicated above open to debate, the approximate edge of  galaxies orbiting around a central black holes perhaps might be a way of defining it.

[Dave Lev (OP)]

Thanks

I couldn't find the relevant data about the SMBH in the Milky Way, however I have found the following info about the black hole in NGC 1365 which is currently as massive as several million Suns.

dailymail.co.uk/sciencetech/article-2285483/The-supermassive-black-hole-spinning-speed-light--holds-galaxys-history.html

"The sphere more than 2 million miles across - eight times the distance from Earth to the Moon - is spinning so fast that its surface is traveling at nearly the speed of light."

So, we have the radius and the velocity which is at nearly the speed of light.

I wonder if we can find similar relevant data about Sagittarius A*.

[Bill S]

Interesting link, Dave.  I read it in spite of my mistrust of anything emanating from the Daily Mail.

It would be good to find out if much has come of this in the 5 years or so since the discovery. 

WHY DOES A BLACK HOLE SPIN?

Is it me, or is this question not answered?

[evan_au]

Our central black hole is remarkably quiet.

I think this is the key - our central black hole doesn't have a real accretion disk at present. But a star traveling too close could easily be torn apart and produce one, at least for a short time. The presence of jets from the center of our galaxy, emitting radio waves and gamma rays suggests that our central black hole had an active accretion disk at various times in the past.

It takes a continual inflow of matter to produce a continuous accretion disk - maybe now it's just having a rest?

There was a recent announcement of 12 black hole binaries found within about 4 light-years of the center of our galaxy.
- This is a case where a small black hole is swallowing matter from a nearby star, and creating an accretion disk around a smallish black hole.
- This shows that current X-Ray telescopes are able to see beyond the dust in the center of our galaxy, and spot accretion disks - if they are present.
http://www.abc.net.au/news/science/2018-04-05/x-ray-black-hole-binaries-supermassive-sagittarius-a/9617254

WHY DOES A BLACK HOLE SPIN?

For a stellar-mass black hole, the star from which it formed had an initial rotation. As the core of the star is crushed, this spin is transferred to the black hole.
For a galactic-center black hole, the matter in the center of the galaxy has an overall angular momentum, and this is transferred to the central black hole as more matter falls in.

[guest45734]

I couldn't find the relevant data about the SMBH in the Milky Way,

This might interest you, the centre of our milky way may have 1000's of blackholes https://www.npr.org/sections/thetwo-way/2018/04/04/599437677/new-study-shows-the-center-of-the-milky-way-has-thousands-of-black-holes

[Dave Lev (OP)]

I couldn't find the relevant data about the SMBH in the Milky Way,

This might interest you, the centre of our milky way may have 1000's of blackholes npr.org/sections/thetwo-way/2018/04/04/599437677/new-study-shows-the-center-of-the-milky-way-has-thousands-of-black-holes

This is very interesting article.
It is stated:
"Isolated black holes are almost impossible to detect, but black holes that have a companion — an orbiting star — interact with that star in ways that allow the pair to be spotted by telltale X-ray emissions. The team searched for those signals in a region stretching about three light-years out from our galaxy's central supermassive black hole."

"What they found there: a dozen black holes paired up with stars, according to a report in the journal Nature."

If I understand it correctly;
We actually see a star orbits around some invisible local center of mass. In the same time we also get an indication for telltale X-ray emissions.
The meaning of tell-tale is: signature.
Is it correct?

So, can you please explain how this telltale (signature) X-ray emission indicates that there is a black hole in the center of the orbiting star?
As it is located only three light-years out from our galaxy's central, then why can't we assume that this emissions it is a direct product of the SMBH itself?

[guest45734]

So, can you please explain how this telltale (signature) X-ray emission indicates that there is a black hole in the center of the orbiting star?
As it is located only three light-years out from our galaxy's central, then why can't we assume that this emissions it is a direct product of the SMBH itself?

Does this link answer your question
https://hub.jhu.edu/2013/06/14/black-holes-x-ray-light/
or maybe this one
https://arxiv.org/pdf/1412.0015.pdf

Hawking radiation escapes from just over the event horizon. https://en.wikipedia.org/wiki/Hawking_radiation

[Dave Lev (OP)]

O.K.

As we have no clue about the radius of the accretion disc in the Milky Way, Do we know the the value in Andromeda Galaxy (or any other spiral galaxy)?

[evan_au]

Do we know the the (radius of the accretion disk) in Andromeda Galaxy?

Detecting the outer edge of an accretion disk is a challenge, because matter is less dense farther out, there is less shear forces and less heating. Overall, the temperature of the outer edge is lower and much less luminous than the inner edge of an accretion disk around a black hole.

Measuring X-Ray fluctuations on very short timescales has allowed estimation of the size of the inner edge of an accretion disk. This is called diskoseismology.
See: https://en.wikipedia.org/wiki/Accretion_disk
(This article has a photo of what may be an accretion disk around a black hole in another galaxy).

On a less dramatic scale, accretion disks around young stars have been imaged.
See: https://en.wikipedia.org/wiki/Protoplanetary_disk

[evan_au]

I found a theoretical paper, looking at a hypothetical mid-sized galactic black hole with a mass of 100 million Suns (the central black hole in our galaxy has a mass of around 4 million Suns).
- Depending on conditions, the radius of the accretion disk could be 60 to 60,000 AU (Astronomical Unit = Earth-Sun distance)
See Figure 5 in http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1992ApJ...385...87C&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf

In some cases, the outer size of the accretion disk is better constrained, for stellar-mass black holes and neutron stars.
This is where there is a binary star system, and the more massive star has exhausted all its fuel and turned into a compact object like a black hole or neutron star (or even a white dwarf).

When the "smaller" star turns into a red giant, it's outer atmosphere is sucked onto the "larger" star, forming an accretion disk.
The size of the accretion disk is constrained by the distance between the two stars, but diameters around 0.5-1.5 million kilometers are typical.

A nice NASA animation here:
https://www.nasa.gov/content/nasa-led-study-explains-decades-of-black-hole-observations

And some size information here:https://apod.nasa.gov/apod/ap020927.html

[Dave Lev (OP)]

Thanks

In the article it is stated:
"We construct simple models of accretion disks surrounding supermassive black holes in active galactic nuclei."

However, I only focus on accretion disc of spiral galaxy which (for my best knowledge) isn't considered as active galactic nuclei.

There are billions of Spiral galaxies and I wonder why there is no valid data about even one accretion disc in this kind of galaxy.

How could it be that we don't know the size of the accretion disc of the Milky way?

[evan_au]

I only focus on accretion disc of spiral galaxy which (for my best knowledge) isn't considered as active galactic nuclei.

It might be more accurate to say that "spiral galaxies no longer have active galactic nuclei".

It is thought that the central black holes formed early on in the universe. In the vigorous, chaotic youth of galaxy formation, large quantities of matter were falling onto the central black hole, creating a big accretion disk and powerful jets of radiation.

However, galaxies have now settled into a more sedate middle age, with most of the matter in fairly stable orbits that do not intersect with each other or with the central black hole. This means that the central black hole is mostly fairly quiet. Maybe the occasional passing star is disrupted, producing a temporary burst of X-Rays.

However, these sedentary galaxies will be violently disturbed every time two galaxies collide. The eventual merger of their central black holes will stir up the dense central area of the newly merged galaxy, producing a significant burst of infalling matter, and a temporary accretion disk.

More information: https://en.wikipedia.org/wiki/Active_galactic_nucleus#Cosmological_uses_and_evolution

[evan_au]

Do we know the the (radius of the accretion disc ) in Andromeda Galaxy (or any other spiral galaxy)?

The broad line emission (from a Type I Seyfert galaxy) arises in a region 0.1-1 parsec across.

For comparison, the closest star to the Sun is about 1.3 parsecs away.

Seyfert galaxies have a visible spiral structure, but the central black hole region puts out a similar amount of power to the rest of the galaxy combined.

See: https://en.wikipedia.org/wiki/Seyfert_galaxy#Type_I_Seyfert_galaxies