Astrophysical simulations predict a new detectable gravitational wave source from collapsing stars

The death of a massive, fast-spinning star can shake the universe. Ripples known as gravitational waves can be sensed by instruments on Earth, according to new research. Published On August 22 Astrophysical Journal Letters. These new sources of gravitational waves await discovery, the scientists behind the research predict.

Gravitational waves emerge following the violent death of stars orbiting 15 to 20 times the Sun. As the fuel runs out, these stars explode and then explode, in an event called a collapser. It is surrounded by material left behind in a large disk behind the black hole, which rapidly spirals into the black hole’s mass. The object’s spin—which lasts for a few minutes—is so great that it distorts the surrounding space, creating gravitational waves that travel across the universe.

Using sophisticated simulations, the scientists determined that these gravitational waves could be detected by instruments such as the Laser Interferometer Gravitational-Wave Observatory (LIGO), which in 2015 made direct observations of gravitational waves from merging black holes. Collapsar-driven waves can help scientists understand the mysterious inner workings of collapsers and black holes.

„Currently, the only sources of gravitational waves we have detected come from the merger of two compact objects, either neutron stars or black holes,” says Ore Gottlieb, a researcher at the Flatiron Institute’s Center for Computational Astrophysics (CCA) in New York. City of York.

„One of the most interesting questions in the field is: What are the possible non-collapse sources that could generate gravitational waves that we can detect with current facilities? One promising answer is now collapsers.”

Gottlieb, along with CCA visiting scholar and Columbia professor Yuri Levin and Tel Aviv University professor Amir Levinson, simulated the conditions, including magnetic fields and cooling rates, found after the collapse of a massive rotating star. Simulations show that collapsers can create gravitational waves powerful enough to be seen from 50 million light-years away. That distance is less than a tenth of the detectable range of more powerful gravitational waves from mergers of black holes or neutron stars, although it is stronger than any uncoupled event simulated so far.

The new findings are surprising, Gottlieb says. Scientists thought that chaotic collapse would create a chaos of waves that would be hard to pick up amid the background noise of the universe. Think of an orchestra warming up. As each musician plays their own notes, it is difficult to distinguish between a melody coming from a flute or a tuba.

On the other hand, gravitational waves from the merger of two objects produce clear, strong signals, like an orchestra playing together. That’s because when two compact objects collide, they dance in tight orbits that create gravitational waves at every turn. This rhythm of identical waves amplifies the signal to a detectable level.

New simulations show that rotating disks around collapsars can emit gravitational waves that amplify together, just like compact objects orbiting in a merger.

„I thought the signal would be very confusing because the disk is a continuous distribution of gas with material rotating in different orbits,” Gottlieb says. „We found that gravitational waves are emitted coherently from these disks, and they are very strong.”

The predicted signal from the collapser disks is strong enough to be detected by LIGO, but Gottlieb’s calculations suggest that a few events may be in existing datasets. Such as the proposed gravitational wave detector Cosmic Explorer And Einstein telescope Dozens can be found a year.

The gravitational wave community is already interested in searching for these events, but it is no easy task. The new work calculated gravitational wave signatures for a limited number of possible collapse events. However, stars span a wide range of mass and rotation profiles, which can produce differences in the calculated gravitational wave signals.

„In theory, we could simulate 1 million collapsars to create a common template, but unfortunately, these are very expensive simulations,” says Gottlieb. „So, for now, we have to choose other strategies.”

Scientists can look at historical data to see if there are any events similar to those simulated by Gottlieb. Although there are many different stars, each with a unique signal, it is impossible to find a match for one of the simulated signals.

Another strategy is to use other signals from near-collapse events, such as supernovae or gamma-ray bursts emitted during the collapse of the star. Same time.

Detecting collapser-generated gravitational waves will help scientists better understand the internal structure of the star during the collapse and learn about the properties of black holes — two topics that are poorly understood.

„These are things we can’t detect,” says Gottlieb. „The only way to probe these inner stellar regions around a black hole is through gravitational waves.”