Gravitational wave hubbub hints at LIGO’s first sighting of a neutron star smash-up

Neutron star collision
An artist’s conception visualizes the gravitational waves given off by a neutron star collision. (LIGO / MIT / Caltech Illustration)

Another big announcement about gravitational waves is coming up, and this time the hints point to  observations in electromagnetic wavelengths as well — emissions of light that may have come from a collision of neutron stars, or a supernova.

That would be a biggie for astronomers: So far, the scientists behind the Laser Interferometer Gravitational-wave Observatory, or LIGO, have detected three confirmed collisions of black holes, but no neutron star smash-ups or stellar explosions.

All will be revealed at 7 a.m. PT on Monday, when representatives from LIGO, Europe’s Virgo gravitational-wave observatory, and a sampling of researchers from 70 other observatories are to share new findings during a briefing at the National Press Club in Washington, D.C.

That was the place where the LIGO team reported its first-ever detection of gravitational waves last year.

The European Southern Observatory is planning a news conference at the same time at its headquarters in Germany.

The fact that so many observatories around the world are in on multiple briefings is a sign that a gravitational-wave detection has matched up with emissions in the electromagnetic spectrum — something that hasn’t been reported previously.

Could this be neutron stars? Advance speculation favors that scenario, because it’s thought that the clash of black holes doesn’t produce light. Last month, scientists said they weren’t able to match up the most recently reported LIGO detection of a black hole merger with any electromagnetic observations.

Unlike telescopes that monitor electromagnetic wavelengths — ranging from radio and infrared, to visible light, to X-rays and gamma rays — LIGO and Virgo look for ripples in the fabric of spacetime. Only the most violent cosmic events, such as supernovae and the mergers of black holes and neutron stars, are strong enough to trigger detectable ripples.

The current hubbub actually dates back to August, when the LIGO team put out the word that astronomers should turn their telescopes toward the galaxy NGC 4993 in the constellation Hydra.

Some astronomers, including the University of Washington’s Peter Yoachim and the University of Texas-Austin’s J. Craig Wheeler, issued tweets hinting at an “optical counterpart” to gravitational-wave observations — and alluding to the possibility that it was a neutron star collision.

At the time, the rumors were picked up by publications including the journal Nature, Science News and astronomer Ethan Siegel’s “Starts With a Bang” blog on Siegel also noted that the Hubble Space Telescope had spotted a candidate for a binary neutron star merger in NGC 4993 on Aug. 22.

In the days before September’s LIGO briefing about a black hole detection, some wondered whether that announcement was going to focus on the neutron star smash-up. Now there’s an even bigger production coming up, and it’s natural to think about neutron stars once again.

One more caveat: An argument could be made that Monday’s announcement will focus on gamma-ray bursts or supernova explosions, rather than neutron stars per se. Some of the astronomers due to speak at the National Press Club specialize in supernova surveys. Others are experts on gamma rays.

Whether it’s neutron stars, supernovae or something completely different, the briefings will be well worth watching.

If the revelations relate to optical observations plus gravitational-wave observations, that would mark a big advance for what scientists call “multi-messenger astronomy” — the ability to combine different ways of detecting extreme phenomena to get a more complete picture of the workings of the cosmos.

Read more: Gravitational wave scientists earn Nobel Prize

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