Tuesday, August 3

Gravitational waves from star-eating black holes detected on Earth | Sciences

There are times when life as an astrophysicist is like being at the bus stop. You wait years for a cataclysmic cosmic event to send shockwaves through the fabric of space-time, and then two arrive at a time.

Years after scientists began their search for a quiver in spacetime anticipated by Albert Einstein, gravitational wave detectors in the US and Europe have detected the first signals from two neutron stars colliding with black holes at hundreds of millions of light years away.

“We are talking about objects that have more mass than the sun that have been eaten up,” said Dr. Vivien Raymond of the Institute for Gravity Exploration at Cardiff University. “We would like neutron stars to be smashed and shredded because then there are many opportunities for interesting physics, but we think these black holes were big enough that they swallowed neutron stars whole.”

The first collision, called GW200105, was detected in data recorded on January 5, 2020 by the US Laser Interferometer Gravitational Wave Observatory (Ligo). The gravitational waves unleashed by the event suggest that a neutron star twice as massive as the sun fell into a black hole nine times as massive as the sun. Moving at the speed of light, these gravitational waves, which squeeze and stretch space-time as they race through the universe, would have taken 900 million years to reach Earth.

Ten days later, Ligo and the Virgo gravitational wave detector in Italy recorded a second distinct signal, called GW200115, which occurred when a neutron star 50% more massive than the sun struck a black hole six times more massive than the sun. Sun. The event was even more distant than the first one a billion light years away. Details are published in The Astrophysical Journal Letters.

Black holes and neutron stars are what remains when stars reach the end of their life and collapse under their own gravity. In some cases, they are born as a pair, in binary star systems where one star orbits another. Neutron stars are among the most exotic objects in the known universe. They are 20 miles wide and have crusts and crystalline cores. They are so dense that a teaspoon of a neutron star weighs as much as Mount Everest.

Personnel working inside the Virgo gravitational wave detector.
The Virgo gravitational wave detector near Pisa, Italy. Photograph: Fresillon Cyril / AFP / Getty Images

Gravitational waves pass through Earth all the time, but tremors in space-time are too subtle to detect unless they are caused by collisions between extremely massive objects. Scientists reported the first gravitational wave detection from the collision of two black holes in 2016 and have since detected waves from neutron star mergers. The gravitational wave record of neutron stars hitting black holes marks another first.

“With these events, we have completed the picture of possible mergers between black holes and neutron stars,” said Chase Kimball, a graduate student at Northwestern University in Illinois. “That does not mean that new discoveries cannot be made with gravitational waves. There are many sources of expected gravitational waves that we have yet to detect, from continuous waves from rapidly spinning neutron stars to nearby supernova explosions, and I’m sure the universe can find ways to surprise us. “


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