[ExI] A odd Gravitational Wave

[Stuart LaForge]

Quoting John Clark:


>
> At 9:02:11 PM Eastern Standard Time on Monday January 13 the 2 LIGO
> detectors in the USA and the VIRGO detector in Italy noticed an unusual
> Gravitational Wave, unlike merging Neutron Stars that produce waves that
> last about 30 seconds and merging stellar mass Black Holes that last about
> a second this one only lasted for 14 milliseconds. Nobody is quite sure
> what caused it, the best guess is a unnovae, they have been observed
> optically a few times in stars too large to go supernova and instead
> collapse directly into Black Holes and just turn off; no supernova has ever
> been observed from a star larger than 18 solar masses although stars well
> over 100 solar masses exist.

Failed supernovae are fairly controversial phenomena and according to  
wikipedia, only two such candidates have been allegedly observed,  
neither of which was in our own galaxy. I don't see how the  
gravitational collapse of such a huge star could be so stealthy since  
matter accretion by black holes is usually one of the brightest  
phenomena that we observe (e.g. x-ray binaries and quasars).

> As it happened this event occurred on a area
> in the sky near to but not precisely at Betelgeuse's location, but
> Betelgeuse is still there and probably isn't massive enough to be a
> unnovae, its eventual fate is probably just a boring old Supernova. And the
> wave could be caused by something else, 14 milliseconds is pretty short
> even for a unnovae.

I don't see how an isotropic gravitational collapse could cause  
gravitational waves. I thought the generation of gravitational waves  
required a dipole or quadripole or some kind of asymmetry. Either the  
star was spinning in which case it should have caused an accretion  
disk with an observable optical or radio signal due to conservation of  
angular momentum. Or the star was not spinning, in which case in  
should have collapsed isotropically and uniformly and not generated  
gravitational waves.

But if it wasn't a failed supernova, then I have no idea what could  
have caused such a short powerful burst of gravitational waves. Very  
mysterious indeed.

Stuart LaForge