Evidence for Black Hole in Galactic Center

[astroron]

Latest on Massive Black Hole in the Galactic Center:eyepop:
http://news.bbc.co.uk/2/hi/science/nature/7774287.stm
Ron

[sheeny]

Got a link, Ron?

Al.

[astroron]

OOOPS Sorry Al
Ron

[xelasnave]

Thanks Ron I like the artist impression but I still wonder about their determination to infer their existence and if there are not other explainations to the observational evidence they seize upon.

I note there is no metion of a companion...as I also read (not something that I wrotre either) that black holes always existed in a binarey system...maybe this one is an exception.
Thanks again I love this stuff.
alex

[sheeny]

I thought that was the evidence... the black hole got it! :lol:

Al.

[jungle11]

I was thinking perhaps many supposed black holes have been found because there was a nearby star to give them away by their effects on that star/ Perhaps that might explain the binary theory?

From that article, it sounds like the really massive ones at the centre of galaxies might have been created in the Big Bang instead of collapsing stars. Which explains how the first stars were born pretty well, and the structure of galaxies too.

What are the other theories apart from black holes to explain the empirical evidence?

[Quark]

Hi Ron,
Andrea Ghez of the UCLA Keck Galactic Centre Group is probably the Worlds leading authority on this. She has been studying the high velocity stars in orbit around the super massive black hole candidate Sag A*(pronounced Sag A star) for over 15 yrs. The star in closest orbit S02, which attains a velocity of 6000 km/sec at closest approach, it has a very elliptical orbit.

In August this year Andrea Ghez reported on her data for a complete orbit of S02. This enabled her to refine not only the mass of Sag A* but also the distance to the Galactic Centre (R0).

I posted her paper on this forum in a post titled "Implications of refining R0"

When I work out how to post a link to it I will include it in another reply.

Regards
Trevor

[Quark]

Hi again Ron,
This is the link to the post I referred to on the super-massive black hole candidate at our galactic centre, Sag A*


http://www.iceinspace.com.au/forum/showthread.php?t=35557


The links to her website are also worth a look, particularly the animation of 15 yrs worth of data of the high velocity stars in orbit around Sag A*.

Regards
Trevor

[DJDD]

I just had a look at the animation of star movements- very cool.
And

Sure, S0-2's orbit was complete but look at S0-16; its 'orbit' looks wild!

and what a difference adaptive optics makes.

[astroron]

Sorry Trevor, I missed your original post.
I have seen data on other places, but this article was saying that this is the definitive proof.
As with the stuff speeding round black holes it is hard to keep up with this subject.
Regards
Ron

[astroron]

Trevor, I missed your post as I was not near a computer for about three months earlier this year;)
Ron

[Quark]

No worries Ron,

There is a lot of info out there on this subject, much of it is somewhat dated, a reflection of the pace at which research is progressing.

We really do live in a golden age of discovery, it is unfortunate that much of it doesn't filter down to the general population.

I became interested in the work of Andrea Ghez back in 2004 when I was doing my degree at Swinburne. I was writing an essay on "The Distance to the Galactic Centre" for Professor Duncan Forbes.

Her work fascinated me, particularly regarding how refinement of Ro (the distance to out galactic centre), by a direct measurement method, would result in a refinement of the absolute luminosity of the variable stars in the Sag A* region. This would then lead to a refinement of the distance ladder.

If you are interested in keeping abreast of the latest research, really in just about any field of astronomy then I would highly recommend the NASA ADS Abstract data base.

Regards
Trevor
:thumbsup:

[bojan]

Alex,
If you read the paper (link provided by Trevor), in abstract it says:

"ABSTRACT
We report new precision measurements of the properties of our Galaxy’s supermassive black hole.
Based on astrometric (1995-2007) and radial velocity (2000-2007) measurements from the W. M. Keck
10-meter telescopes, a fully unconstrained Keplerian orbit for the short period star S0-2 provides values
for the distance (R0) of 8.0 ±0.6 kpc, the enclosed mass (Mbh) of 4.1 ±0.6 ×10 6 M ⊙, and the black
hole’s radial velocity, which is consistent with zero with 30 km/s uncertainty. "

Now, instead of black hole, you can substitute word "object"

What that object could be, in your opinion, considering mass of 4.1 millions Solar masses, in such a small volume of space ?





Black holes of stellar masses (not supermassive, like in centres of galaxies) are sometimes part of binary systems. The paper in question does not deal with those "small" objects.

[xelasnave]

Thanks for all that Bojan:thumbsup:.

Without rattling on I suspect that instead of a single object of massive gravity we will find still massive objects but in binary systems and it is the binary system that produces the extreme gravity..and the massive jets for that matter. (and this science is far to complex to be explained with maths by the way;):lol::lol::lol:) but that was to answer your question and I except your frustration and should not have let it in the door.

Having said that and being entirely sensible for a moment :) I follow and respect all conventional work and read every news release that turns up in the science sites I follow. Anything black or dark I have read about it;).

My objection with black holes is in the name because I got sick a long time ago explaining to folk it was not like a drain hole in the sink:eyepop:... and the disappointment that a realistic relevation dealt them.

Not as appealing if you say think of a ball or think of it like a star..but very dense..denser than me my friend..they then get it... In fact I object to the disposal of many matters to the black basket..black or dark:whistle:.

I would prefer a "Densersiod":D or "Superdensersoild":D or simply Massive stellar object:)...but black hole:shrug:...so unfortunate:screwy: a throw away line used in ridicule has stuck... as did "big bang" .... I think they need a name that gives respect to the profession of astronomy and does not encourage stupid movies.

alex:):):)

[xelasnave]

Also now that we have a mass we can work out how far the force of gravity will reach from our black hole and work out being as massive as they have found it to be just how much it influences the rest of the galaxy..... by the inverse square rule no doubt... so how far does its "power" reach out???

Will we feel any attraction here? where will the attraction die off I wonder?

alex:):):)

[Zuts]

Gravity travels at the speed of light, since the object is only 27,000 light years away and since it has been there far longer than us, we have always felt its attraction...at a tried and true 1/r2 dropoff.

Remember, gravity is a very weak force. A simple fridge magnet can lift a paperclip from the surface of the earth, so the magnetic force of this tiny thing is stronger than the gravitational field of the entire earth!

The 1/r2 dropoff means the force at the surface of the earth compared to the force at the event horizon is gazillions :) of times weaker.

Cheers
Paul

[xelasnave]

Thanks Paul it is the drop off that I point to.
As massive as it is I doubt its influence really goes as far as most may assume. I read something and cant remember a thing but it pays to actually get its actual influence in perspective..it surprised me. and there is other stuff how they clean out only a certain region from recollection...brain is going down hill I am afraid I have had to drop so much data to fit more in...
alex

[leinad]

Thanks for the update. Amazing!

[timb]

They have identified 28 stars orbiting the black hole, so it is minimally part of a 29-ary system.

[xelasnave]

Yes apparently there are a few but there is a difficulty is descibing such a system... its not a 29 ary if they orbit the black hole,,,more like a planetary system in that context... mmm

AND is the black hole at the very center of the galaxy (and how we work out the exact centre would seem difficult) or does it orbit the "centre" in counter balance to its "companions"

I was inclined to think black holes held the rest of the galaxy in place (an incorrect assumption) but it seems they play little part because their gravitational influence does not extend very far at all.

So it is interesting to wonder what their part is in the scheme of things...they do not seem to be anchor points as it were... they are not to the galaxy what our sun is to our solar system in so far we orbit the Sun because of its gravity influence...the solar system does not orbit in the galaxy because there is a black hole at its center... so that is curious.


alex

[jungle11]

I dont think the black whole could be moved by 27 companions? I guess it must be, but the amount would be to negligable to be measured?

I thought perhaps the black hole's gravity well, would be strong enough to attract a layer of stars around it, and then the gravity of those stars would continue to repeat the process, creating the galactic bulge in the centre. Then, further out from the centre the rotation of the galaxy would flatten out the disk? I have no idea - just wondering.

I read something a while ago about galaxies having measurable magnetic fields? Does that explain the structure?

Could our solar system be held in orbit around the core by the combined mass of the billions of stars towards its centre...

[bojan]

Greg,
those 29 stars are just objects in the immediate vicinity of that monster (remember, 4 million solar masses!) and it was possible to (relatively) easily detect and monitor their movement around it. By all means there are more around, invisible to us (at present) which are also orbiting BH.

The mass of BH is so much larger that it stays rock solid in the centre of gravity of that small system (29 stars) ..
However, the whole that bunch orbits the gravitational centre of the galaxy.. Newton's laws are valid here as well. Most likely, the centre of gravity of the whole galaxy is not far away, though.

[timb]

True, the orbiting stars are less to that black hole than the Earth is to the Sun. I was being pedantic. That is one of my special abilities. If you define the MBH as a star, and you seem happy to do so if the BH is of stellar mass, then our friend Sgr A* (http://en.wikipedia.org/wiki/Sagittarius_A*) and the many stars that dance attendance upon it are a multiple star system. There are quite a few papers on arXiv about SMBHs. They generally star close to the galaxy's centre of mass.

[xelasnave]

Thanks for the link Timb.
I highly respect the quality of being pedantic.
For a black hole to exert a gravitational influence even before we apply the inverse square rule it would need a mass to balance the other stars in the galaxy which on current estimate is some 350 billion stars...if we then apply the inverse square rule the black hole would have to be trillions of solar masses...maybe more.
AND so at the risk also of being pedantic I say that this simple observation must remove some of the importance many seek to apply to a black hole.. the significance their gravitational influence I feel is greatly overestimated (in fact not estimated so simple questions such as I raise may be considered) and therefore their role in any influence upon galaxy evolution seems to me be grabbed at without a realisation no matter how massive we believe them to be their mass seems hopelessly inadequate to support current beliefs that they somehow control the galaxy overall...I dont know this is the view of those at the coal face but that is an impression I feel is popular...but it may just be my misinterpretation of various articles that have come before me.

I believe that as a generalisation black holes tend to clean out a region and when this happens they then tend to do little more... they have cleaned out what they can effect gravitationally and their power can not draw in more stars because their gravity can only reach so far to pull in new matter.

Never worry about being pedantic it is better than many other qualities humans put above it.

alex

[bojan]

Alex, do not jump into the pot, without checking what's cooking in it...
You are making conclusions and judgements without any previous analysis (oh.. I wonder what's new about it ;) ) to support such claims.
We have been here before: Science is not a belief system, it is self-sustained system where things get checked and re-checked again and again.. not with words, but with mathematical analysis supported with observations and vice versa.

Have you played with gravitational simulator at all, ever?
Of course, PC is not powerful enough to show how the whole galaxy behaves (with it's BH in the middle) but some time spent with one of them and playing with couple of masses and their interactions may give you an insight into complexity of so simple at a first glance function: 1/r^2.

[astroron]

APOD for today 11/12/08
http://antwrp.gsfc.nasa.gov/apod/astropix.html
:thumbsup:Ron

[xelasnave]

Bojan said........

You are making conclusions and judgements without any previous analysis

I can understand I may seem casual in comment but I dont think anything I have said has been said without thinking long and hard about the stuff I read (leaving aside the alternative idea re black holes which I have left at the door)...and I would say the maths may just support the proposition I ponder upon...

I make a simple observation which is ...a black hole as powerful as we can conceive still will not approach the gravitational power to influence very much of the galaxy ...thanks to the inverse square rule gravitational influence diminishes such that if one were to rely on a black hole having gravitational influence over the whole galaxy it would have to be trillions of solar masses.... and When I get a recharge on this 3g I will look at the stuff I read about black holes clearing out inner regions that came from research not my imagination is my point...and that stuff came from science sites so I am not claiming this is my original thought ...

As to a gravitational simulator yes but what can they tell you if they overlook the simple math I suggest needs to be considered...if a simulator can simulate other than I suggest check it with the simple math... but such is not relevant all that is relevant is a black hole has little gravitational influence on the galaxy... it has or it has not...If we say Sag A is a billion solar masses how far can it influence???.

I dont know really but the way I work out things I am of the current opinion which can be destroyed with simple math or the simple math will support my general proposition...either way I am right or wrong I dont care but my views are not engineered without considerable thought...and I form a belief...there are few facts that can not be termed beliefs irrespective of how convinced folk are of their truth....in my humble opinion...


And thanks Ron for the link but After this psot I will be out of fun tickets for the net so I wont get to look at it till much later.


alex

[xelasnave]

Here is some research on the upper limit of black holes and an a suggestion as to why which indicates why I formed the impression that their role is less than that of apparent popular belief.

http://www.sciencedaily.com/releases/2008/09/080909095133.htm

however we have the prospect of lots of them also

http://www.sciencedaily.com/releases/2005/01/050111090506.htm

alex

[xelasnave]

Black holes are doughnut shaped according to this......
http://www.sciencedaily.com/releases/2008/12/081216104311.htm

well the matter outside follows this shape it seems
alex

[xelasnave]

Rapid spin.....
http://www.sciencedaily.com/releases/2008/01/080110150936.htm
alex

[xelasnave]

Binary black holes
http://www.sciencedaily.com/releases/2002/11/021120072341.htm
alex

[xelasnave]

http://www.sciencedaily.com/releases/2005/02/050222195058.htm

This points to the clean out thing I raised...and suggests an upper mass limit...

alex

[glenc]

http://news.bbc.co.uk/2/hi/science/nature/7815827.stm
A cosmic chicken-and-egg question has been solved by astronomers, who now say that black holes came before galaxies.
The findings were presented at a major astronomy meeting in California.
Most if not all galaxies, including our own Milky Way, are believed to have massive black holes at their cores...

[Paddy]

Yesterday's Astronomy Picture of the Day was a nice infra red composite view of the galactic core, including the cluster around Sag A*. Well worth a look!

http://antwrp.gsfc.nasa.gov/apod/ap090107.html