Aonther massive celestial object, with a companion star in tow,
November 19, 2002 1:29 PM   Subscribe

Another massive celestial object, with a companion star in tow, has been discovered hurtling through the Milky Way. Unlike similar discoveries confirming the bow shock theory of stellar dynamics, this week's phenomenon is considerably older, as it's an aftereffect of the galactic core's formation. The French and Argentine astromoners making the discovery believe what they've witnessed may be a black hole, though theoretically, the collasped matter may be a gravistar.
posted by Smart Dalek (10 comments total)
Another recent news story on black holes: Pair of Supermassive Black Hole Inhabit Same Galaxy, Destined to Collide
posted by Quinn at 1:42 PM on November 19, 2002

As long as it's not a sinistar, we're okay.
posted by yhbc at 1:55 PM on November 19, 2002

Here's hoping that by the time they are 1 light year apart, we will be there in space at the minimum safe distance observing it.
posted by riffola at 2:31 PM on November 19, 2002

Posted this question on Slashdot, but figured I'd throw it out here. Any physicists in the house?

The conclusion about this being kicked by a supernova doesn't make sense to me. Can anyone help me understand? Two problems:

1) The black hole has a companion star, so wouldn't a kick of that magnitude tear it away from its companion and preclude it from acquiring another until it slows?

2) Even ignoring the mass of the companion, the estimates are that the BH is about 7 solar masses. That means that the BH has acquired a kinetic energy of 1/2 * 7 * (2^30 kg) * (10^5 m/s)^2 = about 10^41 J of energy, which is about 1/1000 of the energy of the SN explosion (10^51 erg = 10^44 J). To me, that seems like an exceedingly large fraction of a roughly isotropic explosion converted into motion. It gets even worse if you throw in the mass of the companion.

Anyone have any insights into how this can happen?
posted by ptermit at 3:22 PM on November 19, 2002

ptermit, there's others who could phrase it more eloquently than I could, given my general knowledge of physics:

1) The companion star was snared by the BH long after the bow shock; otherwise, the BH would've absorbed it long before anyone on Earth could observe it.

2) The brunt of the BH's kinetic energy is within the event horizon. The massively dense output is the result of the collapse of the star which formed the BH.

So what actually transpired, in full order, was this:

1) A supernova occurs, with the magnitude of a gamma-ray burster; the shockwave of the explosion extends out toward a neighboring star.

2) Affected by the force of the gamma-ray burster, the neighboring star collapses as it is wrenched from its prior trajectory; depending upon the age of the neighboring star, and its proximity to the nova, it either becomes a neutron star, BH/gravistar, or itself goes nova.

3) The waywardly-traveling survivor of the gamma-ray burster eventually passes yet another star, one which is weaker than the first two. The third object follows the rogue until it is eventually absorbed. (If the third star were closer, and/or larger, it would've collapsed/ been flung, etc.)

Hope that clears things up.
posted by Smart Dalek at 4:24 PM on November 19, 2002

Smart Dalek: Thanks for answering me, but I have to confess that your post didn't clear things up at all.

I didn't understand what you meant by most of (or any of) the black hole's kinetic energy being inside the event horizon. It's just a moving mass, and so has kinetic energy that it can transfer via gravity outside its event horizon, so I can't figure out what you're saying there. Also, companions need not be absorbed by black holes at all; they can orbit indefinitely, just as planets can orbit stars. And I don't see what bow shocks have to do with this, either, as they're produced by shock waves that have already left the star to be accelerated.

Maybe I wasn't terribly clear, or I'm not understanding what's going on here. I thought that these guys saw a fast-moving BH and companion. They concluded that the BH was so fast because it was born in a supernova, which propelled the BH.

My objection is that given the amount of energy in a supernova, the BH is moving too fast, and shouldn't have a companion. It's moving too fast because the SN shouldn't be able to pump so much energy into the star to get it moving like that. It shouldn't have a companion because its original companion should have been torn away, and it's probably moving too fast to acquire a new companion. (And if it did acquire a new one, it must have been moving considerably faster before it did, making the first point even more troublesome.)
posted by ptermit at 8:07 PM on November 19, 2002

Damn the universe sure is cool...
posted by Windopaene at 10:30 PM on November 19, 2002

riffola - what if we're already inside the minimum safe distance? ;)
posted by Songdog at 7:03 AM on November 20, 2002

what if we're already inside the minimum safe distance? ;)
Being an Indian I don't need to use sun block, but I am guessing that would require SPF 1000000 at least.
posted by riffola at 10:34 AM on November 20, 2002

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