Context

Scientists working with the LIGO and Virgo gravitational-wave observatories have detected an oddball event: the merger of two black holes of notably different sizes.

About

• All 10 black hole mergers detected in the first two observing runs had binary components with similar masses.
• But the new event, called GW190412, involved objects of about 8 and 30 solar masses, respectively.
• This asymmetry made the “hum” of overtones in the gravitational waves clear for the first time, enabling researchers to narrow in on the binary’s properties.
• The merger occurred roughly 2 billion light-years away, tilted from our line of sight by about 45°. Before the two black holes came together, the larger one was spinning fairly slowly — roughly 40% the maximum permitted by gravity.
• This is the first time researchers have been able to confidently measure the spin of a black hole about to merge.

GW190412:

• The gravitational-wave observatories detected the signal, designated GW190412, at the start of the third observing run, which happened in two segments spanning April 1 to October 1, 2019, and November 1, 2019, to March 27, 2020.
• The third observing run would have run through April, but was suspended due to the COVID-19 pandemic.
• So far the collaboration has 56 confirmed candidates from this run, two of which now have published analyses. Scientists are actively analyzing the rest.

What is a black hole?

• A black hole is a place in space where gravity pulls so much that even light cannot get out. The gravity is so strong because matter has been squeezed into a tiny space.
• This can happen when a star is dying.
• Because no light can get out, people cannot see black holes. They are invisible. Space telescopes with special tools can help find black holes.
• The special tools can see how stars that are very close to black holes act differently than other stars.