Surprising black-hole discovery changes picture of globular star clusters

Oct 03, 2012
Surprising black-hole discovery changes picture of globular star clusters
Artist's conception of black hole in globular cluster. Credit: Benjamin de Bivort; Strader, et al.; NRAO/AUI/NSF

(Phys.org)—An unexpected discovery by astronomers using the National Science Foundation's Karl G. Jansky Very Large Array (VLA) is forcing scientists to rethink their understanding of the environment in globular star clusters, tight-knit collections containing hundreds of thousands of stars.

The astronomers used the VLA to study a globular cluster called Messier 22 (M22), a group of stars more than 10,000 light-years from Earth. They hoped to find evidence for a rare type of black hole in the cluster's center. They wanted to find what scientists call an intermediate-mass black hole, more massive than those a few or more times the Sun's mass, but smaller than the found at the cores of galaxies.

"We didn't find what we were looking for, but instead found something very surprising—two smaller black holes," said Laura Chomiuk, of Michigan State University and the . "That's surprising because most theorists said there should be at most one black hole in the cluster," she added.

Black holes, concentrations of mass so dense that not even light can escape them, are left over after very have exploded as . In a globular cluster, many of these stellar-mass black holes probably were produced early in the cluster's 12-billion-year history as massive stars rapidly passed through their .

Simulations have indicated that these black holes would fall toward the center of the cluster, then begin a violent gravitational dance with each other, in which all of them or perhaps all but a single one would be thrown completely out of the cluster.

"There is supposed to be only one survivor possible," said Jay Strader, of Michigan State University and the Harvard-Smithsonian Center for Astrophysics. "Finding two black holes, instead of one, in this globular cluster definitely changes the picture," he said.

The astronomers suggest some possible explanations. First, the black holes themselves may gradually work to puff up the central parts of the cluster, reducing the density and thus the rate at which black holes eject each other through their gravitational dance. Alternatively, the cluster may not be as far along in the process of contracting as previously thought, again reducing the density of the core.

"Future VLA observations will help us learn about the ultimate fate of black holes in globular clusters," Chomiuk said.

The two black holes discovered with the VLA were the first stellar-mass to be found in any globular cluster in our own Milky Way Galaxy, and also are the first found by radio, instead of X-ray, observations.

Chomiuk and Strader worked with Thomas Maccarone of the University of Southampton in the U.K., James Miller-Jones, of the International Centre for Radio Astronomy Research at Curtin University in Australia, and Anil Seth of the University of Utah. The scientists published their findings in the October 4 issue of the scientific journal Nature.

Explore further: Thermonuclear X-ray bursts on neutron stars set speed record

More information: "Two black holes in the globular cluster M22," Nature, 2012.

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User comments : 21

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tadchem
1 / 5 (1) Oct 03, 2012
"In the end there can be only One."
hemitite
1 / 5 (1) Oct 03, 2012
Another possibility is that we were lucky enough to these two black holes before their "dance" got out of hand.
gwrede
4.6 / 5 (10) Oct 03, 2012
*** I made a comment, and then I found a flaw in it. ***

But since one can't delete a comment, even within the edit period, you all have to see this text.

*** Please, PhysOrg, let us delete our own comments. ***
Tuxford
1 / 5 (9) Oct 03, 2012
Or just an example of a new galactic core forming, growing from within. Here is an example of one all grown up, having two cores.

http://phys.org/n...arp.html

In SQK physics, two cores are often the result of one spawning the other. I know, inconceivable, to most. But human mental limitations have often been obstacles. Why not yours?
Husky
not rated yet Oct 03, 2012
this makes possible the following rare case: two relative nearby blackholes, of which the expulsing jets collide headon. That would be the ultimate cosmic welding torch.
eachus
4.3 / 5 (6) Oct 03, 2012
Another possibility is that we were lucky enough to these two black holes before their "dance" got out of hand.


My "guess" is that simplifications in the software used to model the globular clusters result in the kick out behavior not seen in reality. (Or perhaps not as frequent as in the simulation.) There are two troubling approximations. Using floating point arithmetic can result in some gravitational forces being ignored totally. (For any floating point notation, there is a delta such that adding delta to 1.0 results in 1.0.) Using double precision is better, but extended or quad precision is often necessary.

The other issue is that the software, for stars sufficiently far away, will add the masses of all the stars in a cube and treat them as a single mass.

Experts in math look at these models and compute a period of time that the simulations can be trusted for. But you will see models that are iffy at less than a billion years used for a much longer period.
hemitite
3.7 / 5 (3) Oct 03, 2012
Thanks eachus.
ValeriaT
1.3 / 5 (3) Oct 03, 2012
Many stellar clusters are remnants of older galaxies, which often contain more black holes at their centers. Actually, the older galaxy is, the higher is the probability, it collided with another galaxy in the past and it adopted its black hole from outside.
Nikstlitselpmur
1 / 5 (3) Oct 04, 2012


The black holes should be producing gravitational waves,predicted to exist by Einstein, but never observed directly or conclusively.
Nikstlitselpmur
1.5 / 5 (4) Oct 04, 2012
sorry, caused by the "pas de deux"
noblackhole
1 / 5 (6) Oct 04, 2012
ALL alleged black hole solutions to Einstein's field equations pertain to an infinite Universe that contains only ONE mass. This means that one CANNOT pile up matter into any given solution of Einstein's field equations. "Black holes were first discovered as purely mathematical solutions of Einstein's field equations. This solution, the Schwarzschild black hole, is a nonlinear solution of the Einstein equations of General Relativity. It contains no matter, and exists forever in an asymptotically flat space-time." (DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY, CRC Press LLC, Boca Raton, USA, 2001). So the claim that they have found two black holes in M22 is false. That there can even be one black hole present in M22 is false. So how can they claim two black holes in M22? Easy: by magic.
Tuxford
1 / 5 (4) Oct 04, 2012
"Contrary to our previous thoughts, globular clusters might be one of the best places to look for black holes, rather than one of the worst," Strader told SPACE.com.

http://www.huffin...704.html

That would be indeed true, if these objects are the primary source of matter for the growth of the clusters. Wake up people. You irrationally rational minds have imprisoned your logic in an intellectual black closet. Where is the counter-rant of @darkdestruction when you need him?
Lurker2358
1 / 5 (1) Oct 04, 2012
When I read this yesterday, I was not one whit surprised.

The notion that the density of a Globular Cluster should increase with time is wrong because Super Novas eject material from the cluster. While it's true the black holes will eat up some material that happens to be ejected from these exploding stars into their direction, but of the exploded material simply escapes into other regions of space, or gets collected by stars on the outside of the cluster.

the result is the core should collapse inward, but the outer stars should move outward over time as total mass of the cluster DECREASES with time due to ejecta.

If black holes really are formed from the gravitational collapse of stars, then Multiple black holes could and SHOULD easily exist. What kind of fool would say otherwise? Black holes do not magically eat up everything or one another. They actually have less total mass and gravity than the original exploding/collapsing star that produced them.

continued
Lurker2358
1 / 5 (1) Oct 04, 2012
The combinations of kinetic energy from the explosion ejectas, radiation pressures, and REDUCED gravity field when a Star explodes into a Supernova and then becomes a black hole, should all push nearby stars FARTHER AWAY as they are impacted by ejected material and interacting with a weaker, less dense gravity field, due to conservation laws. That is, less dense globally. Locally as inside the original core radius of the exploded star the gravity does increase because of the collapse reduces the "r" part of the gravity equation, but these coordinates are below the surface of the original star anyway, and therefore have no gravitational impact on surrounding objects, unless those objects were already on a collision course anyway.

This is one of the biggest misconceptions about black holes anyway, "Oh but it MUST eat up the whole cluster, it's a BLACK HOLE!!". WRONG! It actually has less mass and less total gravity than the original star, even under prevailing theory.
antialias_physorg
5 / 5 (1) Oct 04, 2012
The notion that the density of a Globular Cluster should increase with time is wrong because Super Novas eject material from the cluster.

But since, lacking a pronounced plane of rotation, globular clusters should shrink in on themselves through gravity (no counterforce because not enough angular velocity) that still means that the average density will go up.

the result is the core should collapse inward, but the outer stars should move outward over time as total mass of the cluster DECREASES with time due to ejecta.

Don't confuse mass with density. If mass decreases, but volume decreases faster density increases.
Lurker2358
1 / 5 (4) Oct 04, 2012
At any rate, this is one reason why I've said that Globular Clusters must be some of the youngest structures in the Universe, not the oldest.

If they were old, they should have blown themselves apart by now, leaving only some black holes orbiting one another and a few stray stars, and a bunch of rogue stars spiraling away from the original core.

Instead, they appear as mostly in harmony, implying they are very young and have not had many mass ejections or collisions.

Further, every time one of these new discoveries is made, I say things like this, because the evidence supports my position that Globulars are young, and then there's a big argument and flaming about it.

But this once again agrees with my position.

Anyway, as stated, there's no good reason there wouldn't be 100 or 1,000 black holes in a globular cluster. The scientists assumptions were just wrong and ridiculous, and I have no clue why they thought there would only be one, because it makes no sense to say that.
Fleetfoot
5 / 5 (1) Oct 04, 2012
The notion that the density of a Globular Cluster should increase with time is wrong because Super Novas eject material from the cluster.


Supernovae are quite rare and only occur in massive stars.

The density should increase because the dynamics of the cluster are governed by the Virial Theorem and individual velocities are essentially random. Some high speed stars in the tail of the distribution will exceed escape velocity carrying off kinetic energy hence the potential energy has to decrease, the cluster grows smaller. There are no spectacular "mass ejections" like planetary nebulae, just occasional rogue stars lost from the group.

I do agree that low mass black holes at first sight should just behave like any other similar mass stars in the cluster. The Virial Theorem does mean that more massive stars congregate in the centre though so are more likely to form hard binaries and merge.
yyz
3.3 / 5 (3) Oct 04, 2012
"...I've said that Globular Clusters must be some of the youngest structures in the Universe..."

If clusters are young, every globular cluster should contain at least a few OB stars. How do you account for the complete absence of O and B-type stars in the nearly 160 globular clusters in the Milky Way Galaxy and the globular cluster populations within the Local Group?
Roland
1 / 5 (3) Oct 06, 2012
WaitAMinute! M22 is a globular cluster (a galaxy) "...more than 10,000 LY from earth." But http://phys.org/n...lky.html says our sun is 26,100 LY from the galactic center. M22 must be embedded (or nearly so) in the galactic disk.
Q-Star
2 / 5 (4) Oct 06, 2012
WaitAMinute! M22 is a globular cluster (a galaxy) "...more than 10,000 LY from earth." But http://phys.org/n...lky.html says our sun is 26,100 LY from the galactic center. M22 must be embedded (or nearly so) in the galactic disk.


Uh,,,, the Milky Way contains 100s of 1000s of globular clusters. As do virtually ALL galaxies. Why do you find that to be a "WaitAMinute" moment? We've been mapping them for more than 100 years.

You do know the difference between the terms "globular cluster" and "galaxy" don't ya? If you don't know the subject matter, you really shouldn't be so quick to find a mistake.

By the by: Most of the Messier Objects are INSIDE the Milky Way. Some are nebulae, and MOST are clusters (open globular, closed globular or diffused.)
Lurker2358
1 / 5 (1) Oct 07, 2012
WaitAMinute! M22 is a globular cluster (a galaxy) "...more than 10,000 LY from earth." But http://phys.org/n...lky.html says our sun is 26,100 LY from the galactic center. M22 must be embedded (or nearly so) in the galactic disk.


Globulars are not generally large enough to be considered Galaxies.

Yes, there is at least one "object/cluster" large enough that it is considered a Dwarf Galaxy, which is is inside the Milky Way because it is colliding with the Milky Way. The time scale of this collision is so slow, and the size of the Dwarf Galaxy is small enough, so that we do not experience any conscious awareness of it happening on a daily basis.

Yes, one galaxy can be "inside" another. There are several known cases in astronomy as well, including at least one case of galaxies with retrograde rotation having collided, leaving a ring of spiral arms on the outside counter-rotating the inside arms.

Search for it.