Why LIGO's Black Holes Probably Didn't Come From a Single Star

An anonymous reader writes: Ever since LIGO first announced the direct detection of gravitational waves from two merging black holes, the physics and astronomy community has been struggling to understand an unexpected phenomenon that appears to have come along with it: a short-period gamma ray burst. Arriving just 0.4 seconds after the gravitational waves did, the Fermi satellite's detection doesn't line up with models of black hole mergers. It's thought that short-period GRBs originate from neutron star-neutron star mergers, and so seeing this has led to speculation of new physics, including from Avi Loeb at Harvard that perhaps LIGO's twin black holes came from inside the same star. However, this explanation is exceedingly unlikely, and there are a number of astrophysical explanations that don't require new physics like Loeb's explanation would.

No Forbes link please

[Framboise]

On scientific matter Forbes is really not the appropriate source.

Re:No Forbes link please

[bsolar]

On top of that their site is worthless if you have an adblocker. Slashdot should ban such sites from being eligible as article links.

Re:

[Anonymous Coward]

I have several aggressive ad blockers, privacy guard add-ons and even an ad blocker blocker and Forbes works fine for me. I only need to click deep links twice for some reason.

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[bsolar]

Uhm, maybe it's Reek's Anti-Adblock Killer which does the trick: I'll try with it.

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[radarskiy]

"their site is worthless if you have an adblocker"

They're doing you a favor, since the articles have negative value.

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[MrEd74]

Astrophysicist and author Ethan Siegel is the founder and primary writer of Starts With A Bang.

Re: No Forbes link please

[Fudge Factor 3000]

It looks like it is yet another Startswithabang Forbes article. Only this time it is an AC submission.

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[jfdavis668]

Black holes with accretion disks are pulling the gas from a companion star. Both these stars are now black holes, and underwent supernova explosions which through off any remaining gas. Unless they are orbiting a third star (which survived 2 supernova) or have run into a very dense gas cloud, they have no accretion disks.

No Neutrinos Supports This

[Roger W Moore]

There was also no neutrino pulse detected which the literature suggests should exist if the merger took place near matter. However what I don't understand is the mass of the black holes. I understood that supernovae generated black holes of only a few solar masses, far less than 20+. Now I suppose it's possible that each one had merged before but if they have been wandering around in a region of space filled with stellar remnants surely they would have also picked up an accretion disk too in which case why

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[jfdavis668]

You're right, supernova wouldn't leave black holes of 30M size. These were created by core collapse straight to a black hole without an associated supernova. Maybe that leaves enough remaining material to form a disk?

Warning: Forbes link

[Anonymous Coward]

The last link goes to StartsWithABang.

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[Anonymous Coward]

Speaking of black holes...

Millisecond pulsars

[Anonymous Coward]

There are millisecond pulsars, which are pulsars with a frequency above 1 Hz. The fastest rotating pulsar is PSR J1748-2446ad, with a frequency of 716 Hz. It's estimated that at the surface of the pulsar, at its equator, moves at 24% of the speed of light. It's pretty remarkable, but it's hardly the only millisecond pulsar. Now imagine if during the course of a star's death it became asymmetrical enough that the rotation caused it to develop a dumbbell shape. That could conceivably lead to binary neutron st

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[erebus2161]

Incorrect. They've only confirmed one event, but that doesn't mean that other events haven't been detected since which just haven't been confirmed yet. Also, the one event they've confirmed was detected during the engineering phase before the LIGO upgrades officially went live. We'll need to wait until more events are confirmed, but at the moment it appears as though these events are actually relatively common.

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[jabuzz]

The relativity common is around six events like this a year I believe. Or at least that was what the guy who designed/built a bunch of the electronics in the detector said in the Colloquium on Wednesday if I recall correctly.

My understanding is when the upgrades to advanced LIGO (LIGO was an older detector/experiment) are finished they should be able to detect neutron stars coalescing which is believed to be a far more common occurrence. Probably several times a week; again from memory,

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[ceoyoyo]

IIRC six a year was what they were expecting when they designed LIGO. There was some speculation (not sure how reliable) that that rate might be a bit low, since there were (I believe) two or three other possibilities already in the data.

Hypothetic discussion

[Zorpheus]

It is not clear yet if there was really a Gamma Ray Burst detected. Other articles say that it was probably a fluke of the detector.

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[Muad'Dave]

No, more like a flounder.

Single star to black hole

[John Stock]

Why can't a single massive star collapsing into a black hole not trigger gravitational waves, why does it take two? Surely it's just the mass involved that's the important factor here?

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[Anonymous Coward]

Sources of Gravitational Waves [ligo.org]

"In general, any acceleration that is not spherically or cylindrically symmetric will produce a gravitational wave. Consider a star that goes supernova. This explosion will produce gravitational waves if the mass is not ejected in a spherically symmetric way, although the center of mass may be in the same position before and after the explosion. Another example is a spinning star. A perfectly spherical star will not produce a gravitational wave, but a lumpy star will."

"There

Detection not just creation

[Roger W Moore]

Why can't a single massive star collapsing into a black hole not trigger gravitational waves

It's not just a matter of producing the waves you need to produce a large enough amplitude that you can detect it. Planets orbiting stars should in theory produce gravitational waves too but the masses and accelerations involved create such a tiny amplitude at such a low frequency that even within the solar system we can't detect that source.

Re:Single star to black hole

[ceoyoyo]

The signal they detected has a quickly increasing frequency and amplitude, then a ringdown. You can't get that with a supernova, but it fits well what's expected from a couple of black holes spiraling together and merging. Thriip.

Gravity waves to gamma rays?

[avandesande]

What effect do extremely strong gravity waves have on matter? They are saying that the energy released from this even was equal to 3 suns being converted directly into energy- that is just mind boggling...

What is high-intensity grav radiation LIKE?

[jeffb (2.718)]

This boggles my mind, too -- that much energy radiated away as gravitational waves in a fraction of a second.

I have some referents for electromagnetic radiation -- I know what, say, a kilojoule of light is like, and what it can do when radiated over a few seconds or a few milliseconds. But what would it be like to have your body exposed to a gravitational wave pulse carrying several kilojoules, or megajoules, or terajoules? Would you even notice?