The LIGO observatory made history in 2016 when it discovered gravitational waves from a pair of colliding black holes, proving the existence of both gravitational waves, a century after Einstein predicted them, and black holes. The instrument consists of two L-shaped antennas in Hanford, Washington, and Livingston, La.
Since then, LIGO has been exploring the darkness together with another antenna called Virgo in Cascina, Italy. The combined LIGO-Virgo collaboration consists of around 2,000 scientists around the world. The alphabetical listing of their names and institutions takes up the first five and a half pages of the new paper.
The enigmatic collision that was recorded last August was one of 56 possible gravitational wave events – most of which appear to be black hole collisions – that were detected during the third run of the observatory from April 2019 to March 2020, when the coronavirus Pandemic stopped most scientific activities around the world. The collaboration is still reviewing the data to analyze and confirm it.
Dr. Kalogera said the event was exciting for several reasons. The ratio of the two colliding masses was the most extreme – nine to one – of the gravitational wave collisions observed so far. Astronomers struggle to imagine how such unsurpassed stars could initially come together in a binary binary system.
“This is very difficult to explain for educational theories,” she said.
The signal – a characteristic “chirping” that is caused by the increasingly rapidly circling colliding objects as they approach their moment of final doom – lasted for about 10 seconds. “Due to the favorable circumstances of having observed such a loud signal with very different component masses and for about 10 seconds, we have achieved the most accurate gravitational wave measurement of a black hole spin to date,” said Alessandra Buonanno from the Albert Einstein Institute in Potsdam, Germany, said in a statement by the arm of the institute in Hanover, Germany.
The black hole spin contains important information about the birth and development of the black hole, noted Dr. Buonanno. In this case, the black hole turned out to be “fairly slow”, less than a tenth of the speed that the rigor of Einstein’s theory allowed.
No one had an immediate explanation or candidate for what kind of entity could fill this mass gap – a “shortage,” like Dr. Kalogera called it – except to confirm that the calculations were robust.