Intermediate-Mass Black Hole Found In Omega Centauri

esocid sends us to the European Space Agency's site for news of a new discovery that appears to resolve the long-standing mystery surrounding Omega Centauri, the largest and brightest globular cluster in the sky. The object is 17,000 light-years distant and is located just above the plane of the Milky Way. Seen from a dark rural area in the southern hemisphere, Omega Centauri appears almost as large as the full moon. What the researchers discovered is a black hole of 40,000 solar masses in the cluster's center. From the press release: "Images obtained with the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope and data obtained by the GMOS spectrograph on the Gemini South telescope in Chile show that Omega Centauri appears to harbor an elusive intermediate-mass black hole in its center... Exactly how Omega Centauri should be classified has always been a contentious topic. It was first listed in Ptolemy's catalog nearly two thousand years ago as a single star. Edmond Halley reported it as a nebula in 1677. In the 1830s the English astronomer John Herschel was the first to recognize it as a globular cluster. Now, more than a century later, this new result suggests Omega Centauri is not a globular cluster at all, but a dwarf galaxy stripped of its outer stars. According to scientists, these intermediate-mass black holes could turn out to be baby supermassive black holes."

If it walks like a duck, swims like a duck, quacks

[Latent Heat]

Just because it has a central black hole doesn't make it a dwarf elliptical galaxy.

What distinguishes the Milky Way globular clusters is the the are all about the same, very old, almost as old as the Universe age. If there is reason to believe this is gravitationally bound to the Milky Way instead of some interloper, and if it has the same HR diagram turnoff point of other Milky Way globulars, there is no reason to think it is anything other than one of the bigger and fatter and closer of the globulars.

Re:"baby supermassive black holes.."

[ExploHD]

So can we start calling asteroids "rock lobsters"?

Re:baby galaxy?

[PhxBlue]

I imagine the speculation goes something like this: The dwarf galaxy that is now Omega Centauri collided with the Milky Way, which cannibalized most of the dwarf's stars and sent its star-forming nebulae into the intergalactic void. All that was left of the dwarf was a massive globular cluster.

Another Link

[Anonymous Coward]

In case anyone is inerested, here is a link to the article on Gemini's website:

http://www.gemini.edu/index.php?option=content&task=view&id=284 [gemini.edu]

There are a couple good pictures available.

Re:Omega Centauri appears almost as large...

[Petrushka]

Anyone got a pic to illustrate this? I can't really believe a star to be that visibly large.

Voilà [wikipedia.org]. It looks that large, apparently, because it's about 100 light years across.

what others have said

[Anonymous Coward]

A few of these things only sound bad, but once you do the analysis are not a problem at all. Hard to tell which unless you think hard (which is called science) or read the reports of others who've thought hard:

Sometimes I find myself wondering if there are alien civilizations close enough to supernovae, or black holes (which emit intense x-rays),

A near-by supernova explosion would be absolutely catastrophic, as would straying into the particle stream ejected by a black hole. No good way around that without interstellar flight, so you're pretty much right. Using statistical arguments combined with the known movement of the solar system through the Milky Way along with stellar evolution and the resulting likelihood and expected proximity to Earth of supernovae, there are some astronomers/geophysicists/paleontologists who posit a correlation between major extinction events in Earth's history. For suitably chosen values of the incidence of supernovae over a suitably chosen model of galactic evolution (and thus star formation), and suitably chosen "major" extinction events, this is an intriguing possibility. You can draw a phase clock of extinction events and see a clustering (a "most common" approximate periodicity).

or are in galaxies which suffer collisions,

This actually isn't a problem, although it sounds bad at first blush. Galaxies do of course collide, but the individual stars are so vanishingly small in comparison to their distribution (i.e. they are sparsely distributed) that they essentially never collide. Another way of saying this is that what physicists call the "mean free path" of the particles (stars in this case) is much longer than the scale of the collision. Think of what would happen if you and a friend simultaneously threw a pinch of sand at each other from a distance of many times as far as the moon. In the analogy the grains of sand will be dispersed throughout many cubic miles/kilometers of space by the time the pinches "collide", so you will not be surprised that none of the grains themselves collide. With stars and galaxies, the only interaction among the stars is the gravity of each on every other star. The collisionless nature of galaxy interaction is why we use particle-particle simulations to model galactic collisions: it's the N-body problem and it requires cleverness to avoid the n^2 complexity inherent to the problem.

Look here for some pictures and a little more exposition:
http://www.galaxydynamics.org/spiral_metamorphosis.html [galaxydynamics.org]

And for cosmological-scale stuff:
http://web.phys.cmu.edu/~tiziana/BHCosmo/ [cmu.edu]

or whose home planets are hit by comets.

Technology to survive this threat is much less than you think. It's been available to humans since around 1960-1970. Orbital mechanics was well-established 50-100 years earlier. You just need chemical rocketry and Newtonian mechanics to avert such an ecological disaster; you don't need to abandon the planet or star system. If you can do the latter, you can certainly do the former.

It seems like catastrophes on an astronomical scale are fairly common;

"Common" is relative: it "seems" to me that the occurrence of an extinction-level event on inhabited worlds is relatively rare compared to the time it might take an intelligent species to progress from speciation to advanced space flight; say, 10^5 to 10^6 years. Even if there are few such intelligent species, they will seldom, if ever (statistically speaking), be wiped out by such an event because such an event is incredibly improbable during the tiny window between their initial existence and their developing the means to avert such a disaster.

Of course, statistical models are not physical reality; it might certainly happen occasionally even if you statistically predict "never". Some star might get lucky and bull's-eye another star in a galactic collision.