Unique SOS signal from pulled-apart star points to medium-sized black hole

(Phys.org) —An international team of astronomers, including Texas Tech University's Tom Maccarone, believes they have observed a rare cosmic accident in which a small star is pulled apart by a medium-sized black hole.

The scientists used NASA's space telescope Chandra to detect unusual X-ray activity that, after being analyzed, turned out most likely to be somewhat of a distress call from the pulled-apart star.

"This is the first time anybody has seen anything like this," Maccarone said. "But it's still an open question: is this something extremely rare or are there more events like this happening all the time. Either way, evidence of intermediate-sized , if this interpretation of the data can be confirmed, is a tremendous discovery."

The X-ray signals captured on the edge of nearby galaxy Messier 86, initially revealed two small emissions with a pause of 4,000 seconds in between. Another 4,000 seconds later the quantity of X-ray radiation suddenly increased by a factor of 100 and then gradually decreased again. The activity was very similar to the signal predicted for a medium-sized member of the black holes family, which pulls apart a so-called white dwarf (the remnants of a star like Earth's sun).

This intermediate size would, therefore, be far heavier than the black holes that arise from supernova explosions in the present-day universe – those black holes are about 10 times as heavy as the sun. At the same time, the medium-sized black holes are far smaller than the black holes at the core of galaxies, which are one million to one billion times heavier than the sun. Both of these are regularly observed, whereas a medium-sized black hole isc not.

The timescale of 4,000 seconds concurs with the time needed for the material from the star being pulled apart to rotate once around the black hole, as long as the black hole is about 10,000 times as heavy as the sun. These medium-sized black holes could have arisen early in the history of the universe from the first generation of supernovae. The space around galaxies should, therefore, be full of these, but up until now there was very limited evidence for the presence of this intermediate-type black hole.

The team of astronomers, led by Peter Jonker (Space Research Organization of the Netherlands), seems to have provided the missing evidence. The research results have been published in the The Astrophysical Journal.

"This is probably the tip of the iceberg because we have found more of this strange type of X-ray flash," Jonker said. "Aidan Glennie, a doctoral student at Oxford, is working with me on a study of two comparable signals from different galaxies. As the chances of such a black hole capturing a star and pulling it apart is very small, this means that there are probably many medium-sized black holes."

If more medium-sized black holes are found, that would make it more plausible that super-heavy black holes evolved from the merging of medium-sized black holes. The presence of super-heavy black holes in the early universe in particular, is difficult to explain if there are no medium-sized black holes.

The astronomers also hope it will be possible to observe the merging process in the near future with the improved LIGO and Virgo facilities, and the e-LISA space facility. Astronomers hope to use these to measure the gravity waves transmitted by two merging medium-sized black holes.

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More information: arxiv.org/abs/1310.7238
Journal information: Astrophysical Journal

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Nov 06, 2013
Astronomers hope to use these to measure the gravity waves transmitted by two merging medium-sized black holes.

You realize the probability of looking in the right direction at the right time to see that is absurdly low right? Like I don't even know how to calculate how low it is, but given the time scales you are talking about, and the masses, these events probably don't happen very often at all any more, because the modern Universe is relatively stable.

You've found one probable medium black hole, and what looks like a handful of additional candidates in the entire universe.

Have you guys even observed a stellar mass black hole merger yet? I've heard of observation of BH eating stars, white dwarfs colliding, neutron stars colliding....I've never seen a report of an actually observation that is best explained by a black hole merger. Maybe it happened and I'm not aware, but if it did, nobody is talking about it.

You'd need to be looking at something ridiculously large....

Nov 06, 2013
...like looking at colliding star clusters within a galaxy, perhaps, and I guess you might need a heck of a lot of luck, because not all collisions would involve any medium mass BH, and not all collisions which involve at least one would involve two, and not all collisions involving two star clusters, each having a medium mass BH, necessarily produce a medium mass BH merger.

It's almost like the freaking Drake equation.

P = K^2*L*M

K is the probability of an individual star cluster having a Medium BH.
L is the probability of the two star clusters in question colliding
M is the probabiltiy that the two Medium BH will actually come close enough to merge among all possible cluster collisions.

P is the total probability of a Merger, which is absurdly low compared to ordinary stellar phenomena.

Don't forget the probability that you're looking in the right direction, and the probability that you're looking at the right time.

Nov 06, 2013
"You realize the probability of looking in the right direction at the right time to see that is absurdly low right?"

Gravity wave detectors typically survey large regions of the sky. Detections by multiple GW telescopes are used to localize GW signals: http://arxiv.org/...1791.pdf

"You'd need to be looking at something ridiculously large...."

In this case, M86 is probably the second largest galaxy in the Virgo Cluster after M87, with an estimated mass of well over a trillion solar masses: http://arxiv.org/.../0005243

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