Sunday, October 01, 2017

Gravitational radiation redux + Nobel speculation

This past week, there was exciting news that the two LIGO detectors and the VIRGO interferometer had simultaneously detected the same event, a merger of black holes estimated to have taken place 1.6 billion lightyears away.  From modeling the data, the black hole masses are estimated at around 25 and 30 solar masses, and around 2.7 solar masses worth of energy (!) was converted in the merger into gravitational radiation.  The preprint of the paper is here.  Check out figure 1.  With just the VIRGO data, the event looks really marginal - by eye you would be hard pressed to pick it out of the fluctuating detector output.  However, when that data is thrown into the mix with that from the (completely independent from VIRGO) detectors, the case is quite strong.

This is noteworthy for (at least) two reasons.  First, there has been some discussion about the solidity of the previously reported LIGO results - this paper (see here for a critique of relevant science journalism) argues that there are some surprising correlations in the noise background of the two detectors that could make you wonder about the analysis.  After all, the whole point of having two detectors is that a real event should be seen by both, while one might reasonably expect background jitter to be independent since the detectors are thousands of miles apart.  Having a completely independent additional detector in the mix should be useful in quantifying any issues.  Second, having the additional detector helps nail down the spot in the sky where the gravitational waves appear to originate.  This image shows how previous detections could only be localized by two detectors to a band spanning lots of the sky, while this event can be localized down to a spot spanning a tenth as much solid angle.    This is key to turning gravitational wave detectors into serious astronomy tools, by trying to link gravitational event detection to observations across the electromagnetic spectrum.  There were rumors, for example, that LIGO had detected what was probably a neutron star collision (smaller masses, but far closer to earth), the kind of event thought to produce dramatic electromagnetic signatures like gamma ray bursts.

On that note, I realized Friday that this coming Tuesday is the announcement of the 2017 Nobel in physics.  Snuck up on me this time.  Speculate away in the comments.  Since topology in condensed matter was last year's award, it seems likely that this year will not be condensed matter-related (hurting the chances of people like Steglich and Hosono for heavy fermion and iron superconductors, respectively).  Negative index phenomena might be too condensed matter related.   The passing last year of Vera Rubin and Debra Jin is keenly felt, and makes it seem less likely that galactic rotation curves (as evidence for dark matter) or ultracold fermions would get it this year.  Bell's inequality tests (Aspect, Zeilinger, Clauser) could be there.   The LIGO/VIRGO combined detection happened too late in the year to affect the chances of this being the year for gravitational radiation (which seems a shoe-in soon).

3 comments:

Ben Powell said...

Berry and Aharanov

Douglas Natelson said...

That’s my annual choice, but I have been wrong several years in a row....

Daniel Mittleman said...

Rai Weiss and Kip Thorne. Count on it.