# Blackhole at the center of each galaxy, think again

1. Jun 7, 2005

### Anomalous

If there a massive blackhole at the center of each galaxy then; near the center of our galaxy, stars should be revolving the BH at very high speeds, hence we should be able to note their revolutions around the BH in months, days or even hours.

And hence we should also be able to see some of the stars being hidden behind the blackhole for sometime, giving us opportunity to study the BH in detail. If all these thing happen then yes there must be a blackhole at the center of each galaxy.

2. Jun 7, 2005

### tony873004

Stars do move fast at the center of the Milky Way. Here's an animation:
http://antwrp.gsfc.nasa.gov/apod/ap001220.html

The distance to other galaxies, as well as gas and dust obscuring the view would make it difficult to create such a simulation for other galaxies.

Black holes are very small. The odds of the black hole eclipsing a neighboring star would be very small.

3. Jun 7, 2005

### Staff: Mentor

If they are close to it, yes....
Well, black holes aren't all that "big" that they would "hide" stars. There would be some lensing though, that could make the gravitational fields "visible".
As it stands, such evidence does exist for some galaxies.

4. Jun 7, 2005

### Anomalous

1) We are always interested in facts not animations, we have lot of them with us on various topics.

2) First we should study our own; when technology allows us for latter, we will move on.

3) I Think Sir Russ Watters answered that. Anyways the odds are there and U r forgetting that there are millions of star revolving in our galaxy that can get ecilpsed by that blackhole being at the center of galaxy. so Watch out.

5. Jun 7, 2005

### Anomalous

Please, let us know that too.

6. Jun 7, 2005

### tony873004

1. That animation is a sequence of photographs, not some artist's renditioning. The caption tells you what is going on. It is one picture per year, in infared of the center of the galaxy. So the animation is factual.

2. I agree, but your original question asked about If there a massive blackhole at the center of each galaxy then.... I was simply trying to explain why similar photographic animations do not exist for the centers of other galaxies.

3. I agree Sir Russ Watters answered that, but I'm not just recyclying his answer. Check the order of the posts.

I'm not forgetting that there are millions stars that are candidates for eclipse. Actually there are billions. But when you consider the angular size of these stars, the angular size of the black hole, and the enormous spacing between stars, an eclipse would still be very rare. Maybe we'll live to see one, but the odds are astronomically stacked against it.

7. Jun 7, 2005

### pervect

Staff Emeritus
As you point out, the actual facts are that very rapid stellar motion in the core of our galaxy near Sgr A has already been observed, and provides good evidence that Sgr A at the core of our galaxy is a black hole.

I was looking for a good web reference, as I originally found this information on televised lecture from UCSD, but frankly the "attitude" that you referred to from our poster turned me off enough that I didn't feel like bothering.

Our poster ("anomalous") seems to like threads of the sort "2+2=4, think again", followed by a lame argument - if you check out the relativity forum, you'll see what I mean.

8. Jun 7, 2005

### DaveC426913

We don't see those things, true. But it is not because they are not there, it is because, well... we can't see them.

We can't actually see the core of our own galaxy. It is hidden by dust lanes.

And yes, your attitude is somewhat off-putting. (Doh! All those years studying - if only we had consulted Anomalous!) If you're not careful, you may find your reputation preceding you.

9. Jun 7, 2005

### pervect

Staff Emeritus
We are actually starting to be able to see the core of OUR galaxy with IR telescopes. The longer wavelengths can penetrate the dust.

We cannot now and are not likely in the near future to be able to pick out individual stars in the cores of distant galaxies, however. With the long wavelengths required to see through the dust, unreasonably large mirrors would be required to achieve the required angular resolution.

There's some data on the proper motion of stars near the galactic center at

http://www.mpe.mpg.de/ir/GC/prop.html [Broken]
http://www.mpe.mpg.de/ir/GC/res_s2orbit.html [Broken]

some other links on the page describe the Sharp I infra-red telescope system that was used to take these pictures.

Last edited by a moderator: May 2, 2017
10. Jun 8, 2005

### Anomalous

1) thats your mistake and suggestion.

2) This is not the only forum in the world, I will be where I am treated with respect and dignity.

You seem to be DAVE from AstronomyForums.net, What r U doing here ? Tarnishing the reputation of PF to increase your Ratings ?

11. Jun 8, 2005

### Daminc

Do on to others that which you would have done on to you

12. Jun 8, 2005

### Anomalous

QUOTE=Daminc]Do on to others that which you would have done on to you

Perfect !

13. Jun 8, 2005

### Daminc

Thank you

14. Jun 8, 2005

### Janus

Staff Emeritus
When you've shown that you deserve such, you will be treated with such. So far, you are not off to a very promising start. If This does not meet with your satisfaction, then by all means, be my guest and post at another forum.

15. Jun 8, 2005

### Dr.Brain

Well, most of the stuff which you think must happen for BH to exist at the centre of the universe have shown their presence and we have almost assured the fact that BH do exist at the centre of universes.

For your second fact , the stars wouldnt be hidden but the images of the stars as looked above the black hole would be blurred due to the strong gravitational field which wont light come to us in a way it should have.

16. Jun 8, 2005

### Anomalous

I always do , so dont tell me what a forum is missy. I just found this one Yaa but its an irreekee one. Anyways please stick to the topic madam.

17. Jun 8, 2005

### Anomalous

Thanks for not being arrogant as others sir. U r the first one here to answer straight to the bussiness. U sound very promising about eclipse effects.

AS the stars move from behind the black hole even if they wont get obstructed by the BH yet we should see the space bending effects.

Last edited by a moderator: Jun 8, 2005
18. Jun 8, 2005

### El Hombre Invisible

I'm in stitches. Where are you from, Anomalous? A juggernaut factory, I expect.

19. Jun 8, 2005

### Dr.Brain

Actually,there have been debates on what would be visible when we are inside a black hole?...the answer is pretty straight-forwards, we will see an exact blurred copy of original universe.

And what would person outside BH would see if his friend is inside the black hole?...He would probably see nothing because light wouldnot escape the black hole.

One thing more, as I saw in your first post that stars would orbit faster near the black hole due to its strong gravitational field, but to be more specific, the stars near a black hole moving at enormous speeds are not orbiting but are being 'sucked' in. Its only outside the 'event-horizon' of a black hole that stars 'orbit' and are not 'sucked' in.

20. Jun 8, 2005

### Anomalous

Talk about the topic Mr. OffTopic

21. Jun 8, 2005

### El Hombre Invisible

Why? Do you have any further questions? I thought you were done with black holes and were just offending people for laughs now. I wanna talk instead about how we might get you your own radio chat show where you invite prominent scientists, artists, musicians, politicians, etc. onto the show, ask them a question and, when they answer it, you can lay into them with an unrelated diatribe for half an hour, deliberately misunderstanding everything they say to make it seem like they've just incited your verbal violence. I'm not kidding, EVERYONE would listen to that show. It would be such a success. Stardom, television, guest appearances as yourself in films... all would follow. With my ideas and your childishly innocent and yet aggressively offensive attitude, we could go far. I can already smell the money.

Joe Pesci HAS to play Anomalous in Altman's PF: The Movie!

22. Jun 8, 2005

### εllipse

The only problem is the "prominent scientists, artists, musicians, politicians, etc." will stop agreeing to appear on the show.

23. Jun 8, 2005

### El Hombre Invisible

Yeah, it couldn't be live. We'd need to do loads of shows in advance, Ali G style. We could always lie and say it's gonna be a different show. It's radio after all - they won't recognise him. You want in?

24. Jun 8, 2005

### SpaceTiger

Staff Emeritus
This is simple enough to calculate. In fact, we need only a little high school science:

$$P^2=\frac{4\pi^2a^3}{GM}$$

which is Kepler's Third Law. How close do the stars have to be to be moving with, as you say, months, days, or even hours? If we solve for a and remember that the black hole is thought to have a mass of 3x106 solar masses, then we get

$$a=2.4 (\frac{P}{1\ day})^{2/3} AU$$

That's pretty close. Since an AU is the radius of the earth's orbit, would you expect a lot of stars to be smushed in that close? In fact, we have observed a few stars with short orbits and they have, in fact, been used to constrain the mass of the black hole:

Do you know how large a black hole is? The Schwarzschild radius for the one at our center is given by:

$$R=\frac{2GM}{c^2}\simeq 0.06\ AU$$

In order to see a star eclipsed, it would have to be bright enough that we could see it at all. Since only the most massive stars are visible in the galactic center, it should be no surprise that there didn't happen to be one passing right behind it while we were observing.

25. Jun 9, 2005

### Anomalous

Thank for your efforts unlike some irants here.

Frankly speaking as an amature, I would pretend to understand what U said.

BUt R U impling that there is absolutely nothing visible behind the center of our galaxy in this vast universe ? I was expecting some lens effects with multiple images of some objects. At least even if stars are not behind the BH yet we should be able to observe unusual deviations in the orbit of near by stars that are practivcally impossible; but visible due to light bending.

I hope this was my last question. I have a habit of comming up withnew ones so please dont close this thread.