Starts With A Bang

Beyond Black Holes: Could LIGO Have Detected Merging Neutron Stars For The First Time? (Synopsis)

Two merging neutron stars, as illustrated here, do spiral in and emit gravitational waves, but are much more difficult to detect than black holes. However, they should have optical counterparts, which could lead to the first correlation between the gravitational and electromagnetic sky. Image credit: Dana Berry / Skyworks Digital, Inc.

“Presently thought to be the most powerful explosions in nature… their sources have only recently been localized by observations of associated afterglows in X-rays, visible light, and radio waves, delayed in that order.” -Richard Matzner, on the dictionary entry for Gamma Ray Burst

It seems like an eternity ago, but it’s been under two years since LIGO first began the science run that would first detect merging black holes. Their latest scientific data run is scheduled to end in just two days, and thus far, they’ve announced a total of three black hole-black hole merger discoveries, along with a fourth probable candidate. Yet thanks to the Twitter account of renowned astrophysicist J. Craig Wheeler, a bit of information has leaked: LIGO may have discovered merging neutron stars for the first time.

When two neutron stars merge, as simulated here, they should create gamma-ray burst jets, as well as other electromagnetic phenomena that, if close enough to Earth, might be visible with some of our greatest observatories. Image credit: NASA / Albert Einstein Institute / Zuse Institute Berlin / M. Koppitz and L. Rezzolla.

They’d be approximately ten times lighter than the black holes we’ve witnessed merging, which means the signals are only 10% as strong. In order to get the same amplitude, they’d need to be only 10% as distant, cutting the search volume down to 0.1% the volume. But still, neutron stars may be much more abundant, so we might have a chance. Just yesterday, Hubble observed a galaxy with a binary neutron star inside, just 130 million light years away.

Just four days after Wheeler’s tweet, Hubble observed a binary neutron star merger candidate in the galaxy shown here. Could this be a suspected location of a gravitational wave signal? Image credit: Digitized Sky Survey / STScI.

Could we have just detected a merging neutron star pair for the first time, in both gravitational waves and electromagnetic radiation, together? The rush is on to find out!