Blackhole at the center of each galaxy, think again

[Anomalous]

If there a massive black hole 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 black hole for sometime, giving us opportunity to study the BH in detail. If all these thing happen then yes there must be a black hole at the center of each galaxy.

 

[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.

 

[russ_watters]

If there a massive black hole 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.

If they are close to it, yes...

And hence we should also be able to see some of the stars being hidden behind the black hole for sometime, giving us opportunity to study the BH in detail.

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".

If all these thing happen then yes there must be a black hole at the center of each galaxy.

As it stands, such evidence does exist for some galaxies.

 

[Anomalous]

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

2) 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.

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

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 black hole being at the center of galaxy. so Watch out.

 

[Anomalous]

...As it stands, such evidence does exist for some galaxies.

Please, let us know that too.

 

[tony873004]

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 black hole being at the center of galaxy. so Watch out.

You've got a little attitude in your response. I'm just trying to help you out.

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 black hole 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.

 

[pervect]

You've got a little attitude in your response. I'm just trying to help you out.

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.

 

[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.

 

[pervect]

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.

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
http://www.mpe.mpg.de/ir/GC/res_s2orbit.html

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

 

[Anomalous]

...

1) (Doh! All those years studying - if only we had consulted Anomalous!)

2) If you're not careful, you may find your reputation preceding you.

1) that's 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 ?

 

[Daminc]

I will be where I am treated with respect and dignity.

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

 

[Anomalous]

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

Perfect !

 

[Daminc]

Thank you

 

[Janus]

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

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.

 

[Dr.Brain]

If there a massive black hole 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 black hole for sometime, giving us opportunity to study the BH in detail. If all these thing happen then yes there must be a black hole at the center of each galaxy.

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 wouldn't be hidden but the images of the stars as looked above the black hole would be blurred due to the strong gravitational field which won't light come to us in a way it should have.

 

[Anomalous]

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.

I always do , so don't 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.

 

[Anomalous]

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 wouldn't be hidden but the images of the stars as looked above the black hole would be blurred due to the strong gravitational field which won't light come to us in a way it should have.

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 won't get obstructed by the BH yet we should see the space bending effects.

 

[El Hombre Invisible]

I always do , so don't 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.

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

 

[Dr.Brain]

AS the stars move from behind the black hole even if they won't obstruct the BH yet we will see the space bening effects.

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.

 

[Anomalous]

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

Talk about the topic Mr. OffTopic

 

[El Hombre Invisible]

Talk about the topic Mr. OffTopic

Why? Do you have any further questions? I thought you were done with black holes and were just offending people for laughs now. I want to 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!

 

[εllipse]

Why? Do you have any further questions? I thought you were done with black holes and were just offending people for laughs now. I want to 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.

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

 

[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 going to be a different show. It's radio after all - they won't recognise him. You want in?

 

[SpaceTiger]

If there a massive black hole 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.

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:

http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...620..744G&db_key=AST&high=41fa938d2e24809

And hence we should also be able to see some of the stars being hidden behind the black hole for sometime, giving us opportunity to study the BH in detail.

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.

 

[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 coming up withnew ones so please don't close this thread.

 

[Dr.Brain]

What ST is saying is that , for a star to be visible behind the galactic centre, the star has to be exceptionally bright since light coming from ordinary stars would be lost behind the BH due to less intensity of its light as compared to exceptionally strong GRfield of a BH

 

[Anomalous]

What ST is saying is that , for a star to be visible behind the galactic centre, the star has to be exceptionally bright since light coming from ordinary stars would be lost behind the BH due to less intensity of its light as compared to exceptionally strong GRfield of a BH

So U mean to say that the stars that are orbiting the BH are not gona show unusual orbits or are their orbits exactly perpendicular to us ?

 

[Dr.Brain]

Ofcourse,the stars orbiting outside the 'event-horizon' of a BH would orbit normally treating the BH as a lump of huge mass , but the stars 'orbiting' very near to the 'event-horizon' would move at exceptional speeds because they are literally being tried to be sucked in . Refer to ST for more information regarding what he said, he might be able to tell you more.

 

[turbo]

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.

Please visit this page and wait for the animation to load. The animation is a composite of 6 years of observation of the black hole in the core of the MW. The orbits of stars affected by the BH are clearly shown.

http://www.einstein-online.info/en/spotlights/milkyway_bh/

 

[SpaceTiger]

So now from the link by Turbo we know that the BH is 20light minutes wide

This is an observational upper limit, meaning the black hole must be smaller than that (we can't actually see it). In actuality, it's probably more like 25 light-seconds wide.

So what is the size of its Event Horizon and is it related with the space bending thing and the light bending. And hence should we not see the nearby stars at wrong places.

If the black hole is close to its theoretically predicted size (~0.05 AU) and the nearest star is around 45 AU, then gravitational lensing effects would be negligible.