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Six billion solar mass black hole in nearby Virgo cluster


Martin
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http://www.astronomy.com/asy/default.aspx?c=a&id=8337

 

M87 is one of the larger galaxies in the Virgo cluster----the nearest major cluster of galaxies near us.

M87 is estimated about three times the mass of Milky.

It has been known for a long time to contain a supermassive black hole, but they did not have an accurate estimate of how massive.

 

The black hole at the center of our galaxy is only about 3-4 million solar. So that puts it in perspective. The one in M87 is estimated 6.4 billion solar.

 

Basically they observe the rates that stars are orbiting the center, and estimate the total mass, and the mass of the dark matter halo, in several ways, and then they model the whole galaxy in a supercomputer and find out what choice of parameters makes it act the way it does. So they simultaneously estimate the black hole mass, and the mass of ordinary matter like stars, and the mass of the surrounding dark matter halo.

The 6.4 is actually a 68 percent confidence interval 6.4 +/- 0.5.

 

There is a technical paper that goes along with this. I will get the link incase anyone wants to look at the details.

 

I looked up the article by Gebhardt and Thomas on arxiv:

http://arxiv.org/abs/0906.1492

The Black Hole Mass, Stellar M/L, and Dark Halo in M87

Karl Gebhardt, Jens Thomas

12 pages, accepted for publication in the Astrophysical Journal

(Submitted on 8 Jun 2009)

"We model the dynamical structure of M87 (NGC4486) using high spatial resolution long-slit observations of stellar light in the central regions, two-dimensional stellar light kinematics out to half of the effective radius, and globular cluster velocities out to 8 effective radii. We simultaneously fit for four parameters, black hole mass, dark halo core radius, dark halo circular velocity, and stellar mass-to-light ratio. We find a black hole mass of 6.4(+-0.5)x10^9 Msun(the uncertainty is 68% confidence marginalized over the other parameters). ..."

 

The radius of a black hole of that mass would be around 12 billion miles.

 

There was a puzzle about quasars that this helps resolve. In the past when people measured the mass of nearby black holes by directly observing stuff orbiting them, Doppler-gauging the speed of the stars, the most they got was figures like 3 billion solar.

But quasars are very distant galaxies with supermassive black holes with stuff spiraling in, and from observing quasars it was estimated that the black holes in some quasars must be at least 10 or more billion solar. So there was this discrepancy. How come some quasars get to have such massive BH if all we can find in our neighborhood are much less massive ones like 3 billion tops. I am just speaking in rough approximation but that was the kind of puzzle it was.

Now people are relieved to find that it is more consistent after all. We have a few (or at least one) in our neighborhood that we can actually observe and that is getting up there in the quasar range of mass.

 

The supercomputer they used to model the M87 galaxy has about 5800 central processor units running in parallel.

 

Another nice thing is the M87 black hole has been observed to have that kind of nifty polar jets that you always see pictures of, where stuff spiraling in at the equatorial disk gets ionized and accelerated along magnetic field line out along the spin axis.

 

Virgo cluster is only 59 million lightyears from here, which is pretty close as these things go.

Edited by Martin
ua
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That's the kind of stuff I like to hear about! Thanks Martin. ;)

 

I'm delighted someone else relishes this kind of news. I just learned of a team that last year used an unusual seredipitous method to deduce the mass of another supermassive BH. This time in the quasar galaxy OJ 287.

 

The mass they got was 18 billion solar.

 

They can't actually see the BH but they keep track of the quasar radiation, which fluctuates over time in a curious way. And from the fluctuations they deduced that the galaxy has a small black hole, several hundred or a thousand times less massive, that is in close orbit around the main one.

 

People may have questions about how they came to this conclusion, but the article was published in Nature magazine which usually means it has been thoroughly peer-reviewed.

 

Anyway somehow, by the record of fluctuating luminosity, they deduced the rate of precession of the orbit, and other characteristics, and also got this 18 billion solar figure for the mass.

 

Here is the article by Valtonen et al that reported the OJ 287 bh mass calculation.

http://arxiv.org/abs/0809.1280

A massive binary black-hole system in OJ287 and a test of general relativity

M. J. Valtonen, H. J. Lehto, K. Nilsson, J. Heidt, L. O. Takalo, A. Sillanpää, C. Villforth, M. Kidger, G. Poyner, T. Pursimo, S. Zola, J.-H. Wu, X. Zhou, K. Sadakane, M. Drozdz, D. Koziel, D. Marchev, W. Ogloza, C. Porowski, M. Siwak, G. Stachowski, M. Winiarski, V.-P. Hentunen, M. Nissinen, A. Liakos, S. Dogru

(Submitted on 8 Sep 2008)

"Tests of Einstein's general theory of relativity have mostly been carried out in weak gravitational fields where the space-time curvature effects are first-order deviations from Newton's theory. Binary pulsars provide a means of probing the strong gravitational field around a neutron star, but strong-field effects may be best tested in systems containing black holes. Here we report such a test in a close binary system of two candidate black holes in the quasar OJ287. This quasar shows quasi-periodic optical outbursts at 12 yr intervals, with two outburst peaks per interval. The latest outburst occurred in September 2007, within a day of the time predicted by the binary black-hole model and general relativity. The observations confirm the binary nature of the system and also provide evidence for the loss of orbital energy in agreement (within 10 per cent) with the emission of gravitational waves from the system. In the absence of gravitational wave emission the outburst would have happened twenty days later."

==excerpt==

It was not until the early 2007 that there were enough data to calculate a definite orbit[11]. The precession rate of the major axis of this orbit is 39.0 degrees per orbit, the eccentricity of the orbit is 0.663, and the mass of the primary black hole is 18.0×10^9 solar masses. These values are reasonable: merging binaries are expected to have eccentricities similar to this at intermediate stages of evolution[20], and the mass of the black hole is at the upper end of the mass range in quasars[21] (which is encouraging, as OJ287 is among the brightest quasars).

==endquote==

 

I havent thought so much about this. And I don't know how far to trust it. But right now I am impressed by the Valtonen et al paper. they seem to have caught a pair of black holes which are spiraling down into each other, on the way to merger, and radiating off the excess energy (which they have to do in order to spiral in closer) by having their orbit generate undulations in the geometry around them---gravity waves carrying off the excess energy

Edited by Martin
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"...they seem to have caught a pair of black holes which are spiraling down into each other, on the way to merger, and radiating off the excess energy (which they have to do in order to spiral in closer) by having their orbit generate undulations in the geometry around them---gravity waves carrying off the excess energy."

 

Have they calculated how long until the merger?

 

Why do they have to radiate off excess energy as they spiral together? Will they accelerate in speed as their orbit gets closer and tighter (like the ice skater with arm out spinning faster as they bring their arms inward)?

 

Are those 12-year periodic outbursts the result of each black hole crashing through the others' accretion disks?

 

Imagine that, the most massive object ever detected. And as a bonus, it has a massive parter.

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Wikipedia on OJ287: They think the two super-supermassive black holes will merge in about 10,000 years.

 

They think the 11 or 12-year periodic outbursts are caused by the smaller one crashing thru the larger one's accretion disk.

 

"The maximum brightness is obtained when the minor component moves through the accretion disk of the [more] massive component at perinigricon." and the feeding frenzy begins and ends. ;)

 

 

http://en.wikipedia.org/wiki/OJ287

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With such staggeringly massive black holes being found one can only wonder if a

cosmic-sized black hole could exist somewhere beyond our observations. Has that

ever been postulated ? Could one of those have fed our universe as a white hole ?

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M87 is one of the larger galaxies in the Virgo cluster----the nearest major cluster of galaxies near us.

 

I was under the impression that the Milky Way was actually a part of the Virgo Supercluster. :confused:

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Virgo cluster is only 59 million lightyears from here, which is pretty close as these things go.

 

 

Yo' I do think that what I said is right about the Virgo cluster. I wasn't (or didn't mean to be) talking about V. supercluster.

A supercluster is more like a "cluster of clusters". Different idea. Higher level collective.

 

Milky belongs to a bunch called the "Local Group", which includes Andromeda and dozen or more others depending on what you decide to count. Maybe 20 if you count more smaller ones.

 

Maybe you could say that the Local Group is one of the clusters belonging to the Virgo Supercluster.

 

But the Virgo cluster (not whatever supercluster, just cluster) is well defined and long established and clearly distinct from the Local bunch.

 

I'm just responding quickly from memory. You can check this with Wiki and perhaps correct me. Anybody else?

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Yo' I do think that what I said is right about the Virgo cluster. I wasn't (or didn't mean to be) talking about V. supercluster.

A supercluster is more like a "cluster of clusters". Different idea. Higher level collective.

 

Milky belongs to a bunch called the "Local Group", which includes Andromeda and dozen or more others depending on what you decide to count. Maybe 20 if you count more smaller ones.

 

Maybe you could say that the Local Group is one of the clusters belonging to the Virgo Supercluster.

 

But the Virgo cluster (not whatever supercluster, just cluster) is well defined and long established and clearly distinct from the Local bunch.

 

I'm just responding quickly from memory. You can check this with Wiki and perhaps correct me. Anybody else?

Thanks.

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"OJ-287 over 3 Billion LY away, 18 Billion solar masses has a 100 Million solar mass SBH in a 12-year orbit around it. They estimated the outer edge of the accretion disk of the bigger one as only about 10 light weeks in diameter.

 

"Ten light weeks is about 0.19 light years, or over 1.1 Trillion miles if my math is correct (60 x 60 x 24 x 70days x 186,000mi/sec = 1.116 Trillion miles) or 10,750 AU, or extending to about the middle of the inner oort cloud. The event horizon radius of an 18-Billion-solar black hole is about 54 Million kilometers or 33.5 Million miles, about a third the distance from the earth to the sun, inside the orbit of Mercury." ~from a few months back

 

How fast does the smaller one whiz past the larger on closest approach? :confused:

Edited by Airbrush
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Airbrush, I have to wimp out on you about OJ287.

This is the kind of surprising thing that makes me cautious so I wait until some other team of researchers weighs in on it. As long as it is just one team, the Valtonen et al, I'm scared. Could there be some other explanation of this 12-year cycle of flashes that they have observed? It is a bold interpretation so I need some time to get used to it and decide if I trust it.

 

However let's do the numbers a little bit AS IF we believe their model.

 

How fast does the smaller one whiz past the larger on closest approach?

 

Let's just do a classic kepler approximation and not worry about relativistic corrections. And say we call the semimajor axis by the letter R because it is somewhat like a radius.

 

Let R be measured in AU (the earth's orbit semimajor) and let period P be measured in years (the earth's orbit period). And let the combined mass be M measured in solars.

 

Then isn't it true that GM ~ R3/P2

 

Since it is a proportionality, we can ignore newton's G.

 

So we just have to put P = 12 years and M = 18 billion solar,

and we can solve for R.

 

You can do that, just multiply 144 x 18 billion and take cube root. It will give the average distance or semimajor, expressed in astro units (AU).

 

But what we want is the average speed. Then you can adjust later for the ellipticity e = 0.66 which they also tell us.

 

The average or "circularized" speed would be 2 pi R/P

This is just back of envelope. I have to go out now but can continue when I get back.

 

OK I'm back at least for the moment. The cube root of 144x18 is 14 and the cube root of billion is thousand. So R must be 14, 000 AU just by kepler law.

 

So a circularized orbit would be taking 12 years to go around 2 pi x 14,000 AU.

 

Now we eat the piece of cake by comparing with earth's orbit speed which is 2 pi x 1 AU every 1 year. This baby is going 14 000/12 = about 1000 times earth speed.

 

You may know that earth speed is about 30 km per second or about 1/10000 speed of light---one ten thousandth, good to remember.

So this guy, on a circularized average basis, is going about one tenth of speed of light. More exactly 11 percent, I think.

 

So far the calculation is really back of envelope. You could even do it in your head, without a pencil.

 

Now they say the ellipticity that they estimate (and they still could have the wrong model and be fantasizing) is e = 0.66.

So we still have to adjust that ballpark figure of 11 percent or 0.11c to allow for going faster when it is close in and slower when it is farther out.

But just using Kepler and some sensible astronomical units we at least have a handle. Maybe that is enough for now. Can continue later. How is this discussion working for you so far?

I was in a big hurry earlier and made an arithmetic blunder but I fixed it. Anybody see mistakes?

======================

 

To continue. We really should call the semimajor by the letter a, instead of R. Intuitively it is an average radius so I'm saying R. The meaning of eccentricity e is that eR is half the difference between the farthest and the nearest (the apo and the peri).

So that means that the nearest is 1/3 of 14,000 and the farthest is 5/3 of 14,000

So at closest approach it seems like the speed is about 3 times the average circularized speed I was talking about later. Holy cow. I find that really hard to comprehend, unless I've done something wrong it seems like at least as a rough estimate the thing is going 33 percent of the speed of light.

That is, factoring in the ellipticity, 3 times the 11 percent we got earlier.

You asked about this. I find this scary and unexpected. Maybe I have made a stupid error. I don't like thinking about an orbital speed like that.

 

There would be some relativistic correction but this is my attempt to get a very simple grip on it using Kepler law, the most classic of the classical.

Edited by Martin
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That's a great answer to a simple but difficult question. 33%C is an incredible speed. They think the 2 outbursts are caused by the smaller one punching thru the accretion disk of the larger one, swinging around the larger one and punching back thru the accretion disk to be flung way out to far side of the ellipse. I wonder how long the interval between the 2 outbursts is? It must be a very tiny fraction of a second if it is moving at 33%C.

 

http://www.caha.es/18-billions-of-suns-support-einstein.html

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I wonder how long the interval between the 2 outbursts is? It must be a very tiny fraction of a second if it is moving at 33%C.

http://www.caha.es/18-billions-of-suns-support-einstein.html

 

 

In general the interval could be several days or weeks, depending on how you picture it. Forgetting about the details of this particular case, suppose the accretion disk is larger than the orbit, and suppose the orbit is circular (for simplicity) and the plane of the orbit is tilted say 30 degrees relative to the plane of the accretion disk.

 

Then in a 12 year orbit, the little one punches thru the disk every 6 years.

 

So we have some leeway, as long as the disk is not a lot smaller than the orbit we can make the interval pretty long duration.

 

The thing we need to do is compare the orbit "R" (semimajor axis) with the estimated size of the disk.

 

They estimated the outer edge of the accretion disk of the bigger one as only about 10 light weeks in diameter.

 

I typed this into google "10/52 light years in AU" and it told me

something over 12,000 AU.

 

And our figure for the orbit semimajor axis (conventionally written "a" but I was calling it "R") was around 14,000 AU.

 

So the orbit and the disk are roughly the same size.

 

The picture I'm getting in my head is that the two bursts might be a substantial fraction of a year apart.

 

The major party is at the focus of the ellipse. I'm picturing how wide the ellipse is near one of its foci.

You know that other Kepler law about equal area swept out in equal time.

 

The whole area of the ellipse is 12 years, equivalent. So on paper you draw the ellipse and you take scissors and cut off one end of the oblong, cutting across the long axis, right at where the focus is. And you judge what fraction of the whole area that nub-end of the oblong is, that you cut off.

 

That fraction of 12 years is how long between bursts. Does this make sense?

=================

 

There are formulas about ellipses we could look up. But suppose we just do this very loosy-goose. The time between bursts is like going on a semicircle with Radius 5000 AU, very fast. Remember we said that the peri-distance was 1/3 of 14,000. And that is about 5000. A semicircle is pi x R and pi is about 3, so the distance traveled is 15,000 AU.

 

And light takes 8 minutes to travel one AU (they told us in 4th grade I think). So let's say the little one is going 1/3 of c for that whole semicircle. (It isn't, and it isn't a semicircle, it is the stub end of an ellipse, but close enough.) So the interval between flashes has to be 8 minutes x 5000 = 40 thousand minutes.

I get that it is 28 days.

 

The big error is that it isn't going 1/3 c for most of that time. It is going slower on average, as it rounds the tight end of the ellipse. So the interval is almost certainly more than 28 days. But this is order of magnitude.

Edited by Martin
Consecutive posts merged.
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