Cosmic Back-Man: Astronomers have captured the first vague gravitational wave signals since a neutron star collided with a black hole. These two cases were detected in January 2020 by LIGO and Virgo Labs. The black hole has completely swallowed up the small neutron star and may be without the accompanying radiation. Evidence of such mixed conflicts opens up the opportunity to learn more about the origin, development and outcome of these unequal pairs.
First The first proof In 2016, astronomers recorded more than 50 cosmic collisions with gravitational waves, LIGO and the Virgo inventor. Usually two star black holes merged, and in a few cases they did Two neutron stars. Intensity connects both partners Unequal masses Were already.
What is missing so far, however, is clear evidence of a mixed twin – the collision of a neutron star with a black hole. There was one in April 2019 Potential candidatesHowever, the data situation was too thin for clear evidence. Another event in June 2020 Brings puzzles Because the second partner was much lighter than a black hole, but slightly heavier than a neutron star.
Two mixed conflicts in a row
Now, for the first time, astronomers have captured clear signals of a neutron star colliding with a black hole. In January 2020, LIGO detectors in the United States and the virgin inventor in Italy recorded gravitational waves twice in a row from such hybrid twins. “Gravitational waves not only tell us the structure of a lighter object, but we can determine its maximum mass,” explains Bhushan Cadre from the Max Planck Institute for Gravitational Physics in Potsdam.
These analyzes show that the smallest partner in both collisions cannot be a black hole, but rather a neutron star due to its low mass. At the event GW200105 on January 5, 2020, a black hole with a mass of 8.9 solar masses and a neutron star with a mass of 1.9 solar masses collided. The energy of this collision emitted gravitational waves that reached Earth about 900 million years later.
The second event was recorded on January 15th. GW200115 comes from a black hole with a mass of 5.7 solar masses and a neutron star with a mass of 1.5 solar masses, which collided about a billion light years away.
Is there any radiation with it?
Because the gravitational waves of this second collision reached good quality for both LGO detectors and the Virgo detector, astronomers were able to determine at least approximately the possible location of the event. Using the triangle, narrow its position to one part of the sky, which is about the size of about 3,000 full moons.
This approximate positioning allowed other teams to use telescopes to search for the electromagnetic effects of the collision. Such bursts of radiation are not uncommon when two black holes collide, but they became clear after the neutron stars merged. Found. However, it is unclear whether they will be released in mixed conflict. At least astronomers have not found anything with GW200115.
Swallowed whole – like back-man
Possible cause: The neutron star may have been swallowed whole by the black hole – leaving no radiation debris. “These are not black holes that first go towards neutron stars and throw scraps like a cookie monster,” explains Patrick Brady, a LIGO spokesman for the University of Wisconsin-Milwaukee. “This emission will generate radiation, but we don’t think it happened in those cases.”
“In these collisions, two massive and dense objects do not come together. It’s like a back-man: the black hole swallows up its neutron star partner completely,” says Susan Scott, co-editor of the Australian National University.
Many questions remain unanswered
The events GW200105 and GW200115 clearly show that these unequal collisions exist internationally – and that they can be detected by gravitational waves. At the same time, however, these collisions open up new opportunities for astronomers to explore in more detail the origin, evolution, and conclusion of such mixed pairs. “We don’t know about neutron stars and black holes – how small or large they are, how fast they rotate and how they merge,” explains Maya Fishbach of Northwest University in Evanston.
LIGO and the Virgin teams are currently upgrading their inventors to become even more sensitive to the next surveillance round in 2022. As the third member of the team, the Japanese Kagra Detector has been in operation since 2020. (Letters from the Journal of Astronomy, doi: 10.3847 / 2041-8213 / c082e)
Quell: University of Wisconsin – Milwaukee, Northwestern University, CNRS, Australian National University