On April 25 and 26, 2019, NSF’s Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European-based Virgo detector registered two new gravitational waves, the ripples in space-time predicted by Albert Einstein. The first was from a neutron star crashing into another neutron star 500 million light-years away, and the second was from a neutron star gobbled up by a black hole 1.2 billion light-years away. If confirmed, the second event will be the first of this kind to be detected.
The twin detectors of LIGO — one in Washington and one in Louisiana — along with Virgo, located at the European Gravitational Observatory in Italy, resumed operations April 1, 2019, after undergoing a series of upgrades to increase their sensitivities to gravitational waves.
Each detector now surveys larger volumes of the Universe than before, searching for extreme events such as smash-ups between black holes and neutron stars.
“The latest LIGO-Virgo observing run is proving to be the most exciting one so far,” said Caltech’s Professor David Reitze, executive director of LIGO.
“We’re already seeing hints of the first observation of a black hole swallowing a neutron star. If it holds up, this would be a trifecta for LIGO and Virgo — in three years, we’ll have observed every type of black hole and neutron star collision.”
The April 25 neutron star smash-up, named S190425z, is estimated to have occurred about 500 million light-years away from Earth.
Only one of the twin LIGO facilities picked up its signal along with Virgo. Because only two of the three detectors registered the signal, estimates of the location in the sky from which it originated were not precise, leaving astronomers to survey nearly one-quarter of the sky for the source.
The possible April 26 neutron star-black hole collision, dubbed S190426c, is estimated to have taken place roughly 1.2 billion light-years away.
It was seen by all three LIGO-Virgo facilities, which helped better narrow its location to regions covering about 1,100 square degrees, or about 3% of the total sky.
“The Universe is keeping us on our toes,” said University of Wisconsin-Milwaukee’s Professor Patrick Brady, spokesperson for the LIGO Scientific Collaboration.
“We’re especially curious about the April 26 candidate. Unfortunately, the signal is rather weak. It’s like listening to somebody whisper a word in a busy café; it can be difficult to make out the word or even to be sure that the person whispered at all. It will take some time to reach a conclusion about this candidate.”