Astrophysicists Explain Perplexing Gravitational Wave Observatories Results.

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Simulations of supernova explosions of massive stars paired with neutron stars can explain puzzling results from gravitational wave observatories.

A new study showing how the explosion of a stripped massive star in a supernova can lead to the formation of a heavy or a light resolves one of the most challenging puzzles to emerge from the detection of neutron star mergers by the gravitational wave observatories and Virgo.

The first detection of by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2017 was a neutron star merger that mostly conformed to the expectations of astrophysicists. But the second detection, in 2019, was a merger of two neutron stars whose combined mass was unexpectedly large.

“It was so shocking that we had to start thinking about how to create a heavy neutron star without making it a ,” said Enrico Ramirez-Ruiz, professor of astronomy and astrophysics at UC Santa Cruz.

Compact astrophysical objects like neutron stars and black holes are challenging to study because when they are stable they tend to be invisible, emitting no detectable radiation. “That means we are biased in what we can observe,” Ramirez-Ruiz explained. “We have detected neutron star binaries in our galaxy when one of them is a pulsar, and the masses of those pulsars are almost all identical—we don’t see any heavy neutron stars.”

LIGO’s detection of a heavy neutron star merger at a rate similar to the lighter binary system implies that heavy neutron star pairs should be relatively common. So why don’t they show up in the pulsar population?

In the new study, Ramirez-Ruiz and his colleagues focused on the supernovae of stripped stars in binary systems that can form “double compact objects” consisting of either two neutron stars or a neutron star and a black hole. A stripped star, also called a helium star, is a star that has had its hydrogen envelope removed by its interactions with a companion star.

The study, published on October 8, 2021, in Astrophysical Journal Letters, was led by Alejandro Vigna-Gomez, an astrophysicist at the University of Copenhagen’s Niels Bohr Institute, where Ramirez-Ruiz holds a Niels Bohr Professorship.

“We used detailed stellar models to follow the evolution of a stripped star until the moment it explodes in a supernova,” Vigna-Gomez said. “Once we reach the time of the supernova, we do a hydrodynamical study, where we are interested in following the evolution of the exploding gas.”

The stripped star, in a binary system with… Brinkwire News Summary.

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