Observing black hole mergers (conference on signs to look for, computer sims)

[Martin]

http://www.stsci.edu/institute/conference/blackholemergers

 

An interesting thing you immediately get if you click is eight images.

Four on the left are stills from a computer simulation of a merger, calculated step by step using numerical GR methods.

 

The four on the right are actual photographs, some with false color showing temperature, of real things which look like stages in the merger of supermassive BHs.

 

That is, the observed thing looks somewhat like what they got by running the numerical model.

 

This field is just getting started. Maybe at this point they don't have much more than those eight images. But I'd expect they'll be getting more interesting stuff on observing BH mergers in next few years.

[Airbrush]

The merger of two supermassive black holes seems to me like the most explosive event since the Big Bang. Those things don't like to be pushed around. Does it cause a huge explosion like a supernova or a GRB? Is it more energetic than a SBH devouring a star?

[Martin]

The merger of two supermassive black holes seems to me like the most explosive event since the Big Bang. Those things don't like to be pushed around. Does it cause a huge explosion like a supernova or a GRB? Is it more energetic than a SBH devouring a star?

 

I like this response a lot. I am not an expert on this. What you are saying is that a large amount of gravitational energy is released. That is an alert observation.

 

Like, calculate the gravitational potential energy of two compact masses each of which has a mass of a billion solar----and they are say 100 lightyears apart and they are falling towards each other.

 

I think it is a new field. I think this workshop that the link is to is an early workshop in this line of research. I don't know how or on what timescale the energy is released. They are doing sims and trying to understand the dynamics of this.

 

One reason it's interesting is that they can see this kind of event in process.

 

I think the sheer size may somehow slow the release of energy down.

 

The radius of a solar mass BH is only about 2 miles. (3 km). So when two solar mass BH merge they could be going some goodly percent of the speed of light (I don't know) and it could happen really fast.

 

Radius is proportional. The radius of a 3 million solar BH (like we have at Milkyway center) would be 6 million miles. (9 million km = 30 light seconds).

 

And then some of the BH are a billion solar mass. Offhand I cant figure out what to expect. Maybe if I was in Baltimore MD I'd drop in at Johns Hopkins and visit that workshop.

Edited March 21, 2009 by Martin

[lakmilis]

It is interesting..

 

Ok Could I inject two (sorry, pretty off topic questions somewhat, although they started with this):

 

A. What REALLY is Sagittarius-A*? It's apparently at the edge of our SM-BH, but a star that big??? PLease.. It seems as we only know it more or less as a light source?

 

and B. (ok, this is the off topic one, my apologies beforehand, maybe I should put it as an eternal topic starter which comes up).. Yup, the 'centre of the universe' question.

 

We know that all motion (linear) taken some reference point in space, will be moving away and as such , any reference point taken, will be the centre of the universe seemingly (Doppler effects all that).. HOWEVER, what about rotational movement. Everything in the universe revolves around something... now , in the case of this binary black hole system you mention, the centre is somewhere between them.. they however probably revolve around some other greater system where one could place a new centre point. Now these points are more absolute. If we choose the reference point anywhere i that system, the rotational centre of the system we can observe will remain fixed to the system as such.

 

So techincally speaking, if we could observe allrotation in the universe, we would indeed find a centre point, no? (Would seem as the gravitational centre of the universe).

 

Again, sorry if it is digressing.. If so, I will edit it out and maybe punch up a topicstarter.

 

(Or just disregard the two questions).

 

Also... I am wondering.. S2, moving at around 18 million kilometers per hour... (abt 0.017c). Lets say had a planet system in place around it and there was an 'earth-like' planet there rotating around it such that it would have a g=10 like our Earth. Would the sheer inertial momentum of it's star affect it in any way? (I guess our foolish minds just can't get used to the fact that in space, "resistance is futile" ;p) (PS. This last one is implying your question about the gravitational waves.. as S2 is close to our SMBH in the centre of our galaxy).

[Martin]

Lot of questions, maybe we can share them. I'll take this one:

what is Sgr A*?

 

http://en.wikipedia.org/wiki/Sagittarius_A*

 

Officially it is the radio source associated with the supermassive black hole. Some of the signal is in millimeter band. I don't know what the overall spectrum is like but we could probably find out.

 

Black holes often have processes going on round them that radiate, like the hot accretion ring, and polar jets.

 

The way I think of it, it's all one object. So I think of the 4 million solarmass black hole, and all its accoutrements including the radio source as a single object called Sgr A*.

 

You may have had something different in mind, like what processes might be causing the radiofrequency radiation? If so keep asking. Ask more detailed questions. It's better to be definite even if it's something I or the others can't answer.

[Airbrush]

This field is just getting started. Maybe at this point they don't have much more than those eight images. But I'd expect they'll be getting more interesting stuff on observing BH mergers in next few years.

 

Do they expect to witness a merger in the near future?

[lakmilis]

we see mergers now going on in some binary systems.. ... these processes last thousands and millions of years. It tends to be not celestial events happening suddenly, but rather our equipment which gets better every year (and every half decade we get a new bling bling which helps us). Although of course , once in a while we get a nice flash of something which happened some odd million years ago

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Ye Martin.. Normally I feel things are pretty well guessed at or so, or deduced.. SagA* just seemed a bit weird to me (obviously know the wiki entry, wouldn't be asking about it , if I just needed the wiki thing Ye.. to be honest.. I don't have more specific queston on it right now.. just curious on the overall signature. You think its the whole thing hmmm... I think SagA seems to be more discrete than that... also moving at that speed and with thatsize.. I find it tantalising.. I gave up on where my philosohy was taking me , as my models were predicting quasars of ~5 kHz but till date the fastest we've found are what... 1.5 or so? 2? sigh.. just didn't cut it. So now I just look around the cosmological map in a very Socratean way :/

 

SagA has got me curious though (plus S2 sorry)

[Airbrush]

If a quasar is a supermassive black hole (SBH) devouring matter at the rate of solar masses per month, then my guess is that when two SBH collide, after a long dance around each other, it happens very quickly and a lot of accretion disk material gets dragged around and forced fed into each as they get closer.

 

It should look like a couple of quasars orbiting each other and in the critical moment of collision, there is a massive burst of energy greater than all the galaxies in the observable universe, but just for an instant. Then it settles down to a long meal of accretion disk material so it shines like a mega-quasar for a long time afterwards, unless the impact blasts all the accretion disk material away and out of reach. Or as Martin stated that the intense gravity would slow the energy release?

 

I don't understand gravitational waves so maybe someone else can explain that aspect. I think the processes in quasars are more energetic than gravitational waves. The gravity waves is how we could detect these mergers.

 

Here is an animation of 2 black holes merging and tell me what you think of the discussion that followed it.

 

http://www.newscientist.com/blog/space/2007/05/battle-of-black-holes.html

Edited March 31, 2009 by Airbrush

[lakmilis]

think the burst of energy is a tad over the top :)a supermassive BH has perhaos soem million suns in it mass wise.. that is the energy of one galaxy lets say. you are *not* going to get some energy burst equallign the observable universe hehe.

Edited March 31, 2009 by lakmilis

[Airbrush]

The merger of two SBH seems like the ultimate heavyweight fight.

 

Some SBH have a billion solar masses or more. Consider that a quasar's tremendous energy output is probably the result of an accretion DISK. What if the two SBHs have accretion disks that are not parallel? As they approach each other each tears away the other's accretion disk resulting in matter crashing into both over much broader areas. Instead of accretion DISKS this could result in a chaotic disbursion of matter all around each in an accretion SPHERE, a shell of massive energy outbursts. This could vastly multiply the energy output of both. After each strips away the other's accretion disk then there would be little left but 2 naked black holes which would spin around each other at relativistic speed, and then merge at near light speed. Their tremendous gravity would suppress any other outburst. So I propose that the most energetic phase of the merger would be binary super-quasars leading up to the merger, as each tears appart and starts a feeding frenzy on accretion material, with huge amounts of gas and dust falling every which way into each black hole, all over the spherical event horizons, and not the moment of merger which would only end with a unpresedented spike in gravity waves.

Edited April 1, 2009 by Airbrush

[lakmilis]

there you go.. now you are being more concise. Don't forget that a 'billion' sun masses is the mass of a medium galaxy... .the amount of galaxies in the universe.... staggering... (2 SBHs merging).. still a ' local' phenomenon, local being let's say in a galaxy cluster and vicinity.

[Airbrush]

Maybe some of the long gamma ray bursts are from merging SBHs. Wiki says that the long GRBs (longer than a couple of seconds) are from massive stars collapsing into black holes, and the short ones come from merging neutron stars. I propose that when supermassive black holes merge they would look like binary quasars until the final moment.