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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.
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 stars or, with enough mass, dual black holes. Ethan seems to be going against the prevailing views on what could formed the dual black holes.
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.
Sources of Gravitational Waves
"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 are four main sources of gravitational waves caused by different kinds of motion and changing distributions of mass - continuous, inspiral, burst, and stochastic."
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.