New astrophysics model sheds light on additional source of long gamma-ray bursts

Chopping-edge laptop simulations mixed with theoretical calculations are serving to astronomers higher perceive the origin of a number of the universe’s most energetic and mysterious mild reveals—gamma-ray bursts, or GRBs. The brand new unified mannequin confirms that some long-lasting GRBs are created within the aftermath of cosmic mergers that spawn an toddler black hole surrounded by an enormous disk of natal materials.

Astronomers beforehand thought that black holes that generate lengthy GRBs sometimes type when large stars collapse. Nevertheless, the brand new mannequin reveals that they’ll additionally come up when two dense objects merge, akin to a pair of neutron stars—the dense, useless remnants of massive stars—or a black hole and a neutron star. The findings clarify not too long ago noticed lengthy GRBs that astronomers could not hyperlink to collapsing stars.

The simulation‘s creators present their results in The Astrophysical Journal Letters.

“Our findings, which join observations with underlying physics, have unified many unresolved mysteries within the discipline of gamma-ray bursts,” says Ore Gottlieb, lead writer on the brand new examine and a analysis fellow on the Flatiron Institute’s Middle for Computational Astrophysics (CCA) in New York Metropolis. “For the primary time, we are able to take a look at GRB observations and know what occurred earlier than the black hole shaped.”

GRBs are a number of the brightest and most violent occasions within the cosmos. Since their first detection in 1967, GRBs have dazzled and puzzled astronomers. Even many years later, the precise mechanisms that generate the mighty blasts of gamma rays stay unsure. Through the years, astronomers have observed two distinct populations of GRBs—ones lasting lower than a second and others that linger for 10 seconds or extra.

Researchers finally decided that quick GRBs originate from jets launched after the merger of two compact objects and that lengthy GRBs can happen when jets are launched through the collapse of large rotating stars. However prior to now 12 months, two unusually lengthy GRB observations instructed that collapsing behemoths weren’t the one issues inflicting lengthy GRBs.

Gottlieb and his colleagues ran state-of-the-art simulations to check how mergers of large compact objects can spark GRBs. The brand new simulations took months to run and have been partly performed on one of many Flatiron Institute’s supercomputers. The brand new simulations begin when the 2 compact objects are in an in depth orbit and comply with the jets till they’re removed from the merger web site. This strategy permits the researchers to make fewer assumptions in regards to the physics concerned.

By combining the simulations with constraints from astronomical data, the scientists constructed a unified mannequin for the GRB origins.

The researchers decided that the bizarre GRBs are generated after a merger between two compact objects. After merging, the objects create a black hole surrounded by a big accretion disk—a quickly rotating doughnut of magnetically charged leftover materials—that may pump out lengthy GRBs. This data from the simulation helps astronomers perceive not solely the objects creating these GRBs but additionally what got here earlier than them.

“If we see a protracted GRB like those noticed in 2022, we now know that it is coming from a black hole with a large disk,” Gottlieb says. “And figuring out there’s a large disk, we now can determine the ratio of the lots of the 2 parental objects as a result of their mass ratio is said to the properties of the disk. For instance, the merger of unequal-mass neutron stars will inevitably produce a long-duration GRB.”

The scientists hope to make use of the unified mannequin to establish what objects create quick GRBs. These bursts, the mannequin suggests, may very well be brought on by black holes with smaller accretion disks, or they could come from an object referred to as a hypermassive neutron star, which is an unstable type of the star that shortly collapses to type a black hole however not earlier than it pulses out quick GRBs.

The scientists hope that with extra observations of GRBs, they’ll additional refine their simulation to find out all GRB origins. Although GRB sightings stay comparatively uncommon, astronomers goal to seize many extra when the Vera C. Rubin Observatory begins observing in early 2025.

“As we get extra observations of GRBs at completely different pulse durations, we’ll be higher in a position to probe the central engines powering these excessive occasions,” Gottlieb says.