Deep-space discovery: Oddball gamma-ray burst forces revision of theoretical framework

The mysteries of the cosmos proceed to amaze astronomers, and with every new remark comes an opportunity to deepen—or upend—our understanding of the universe.

Within the Dec. 7 difficulty of the journal Nature, a global workforce of astrophysicists report the invention of a singular cosmological gamma-ray burst (GRB) that defies prevailing theories of how the violent cosmic explosions type. This “oddball” burst led the workforce to suggest a brand new mannequin, or supply, for sure sorts of GRBs.

Gamma-ray bursts are probably the most luminous and violent explosions within the universe. They signify the deaths of stars or collisions of stellar remnants. Noticed GRBs are sometimes positioned into two classes: short- or long-duration GRBs. Lengthy GRBs originate from the deaths of large stars, and are sometimes related to brilliant optical transients named supernovae. Quick GRBs have a length of lower than two seconds and originate from the collisions of two neutron stars or a neutron star and a black hole, and are sometimes related to extra faint optical transients referred to as kilonovae.

For many years, GRBs nestled properly into these cozy classes. Till now.

On Dec.11, 2021, a GRB triggered a number of gamma-ray detectors in space, together with NASA’s Fermi Gamma-ray Telescope and the Neil Gehrels Swift Observatory. This burst, with a length of almost 70 seconds, would sometimes be thought to be a standard lengthy GRB. That’s, till a number of groups from the U.S. and Europe carried out follow-up observations and found a shocking signature.

“This GRB contains two elements: a 13-second lengthy arduous spike and a 55-second softer prolonged emission,” stated UNLV alumnus and research corresponding writer Bin-Bin Zhang, who’s at the moment with China’s Nanjing College. “The length of the 13-second arduous spike ought to have fully excluded this burst from the quick GRB class.”

In different phrases, as an alternative of displaying a a lot brighter supernova, as anticipated, the remark was in line with a kilonova that’s extra sometimes related to a brief GRB.

“Such a peculiar GRB was the primary of its sort ever detected,” stated UNLV astrophysics professor Bing Zhang, co-corresponding-author of the Nature paper. “This discovery not solely challenged our understanding of GRB origins, it additionally requires us to think about a brand new mannequin for the way some GRBs type.”

The analysis workforce believes that this distinctive GRB, referred to as GRB 211211A, doubtless fashioned by means of collision between a neutron star and a white dwarf, what’s referred to as a WD-NS merger.

White dwarfs are earth-sized objects that type from the dying of low-mass stars—these with a mass smaller than that of about eight of our Suns. Neutron stars type when extra massive stars, these with a mass of between about eight and 20 Suns, die off. When even bigger stars die, they type black holes instantly.

Huge, low-density stars make long-duration GRBs whereas high-density stars, together with neutron stars, make quick length GRBs. In keeping with UNLV’s Zhang, white dwarfs have intermediate densities, which make them perfect origins for the kind of GRB found in 2021 because it shows an intermediately lengthy length with out involving a large star.

“Regardless of the comparatively giant variety of GRBs noticed annually, the distinctive signature of GRB 211211A pushed the envelope of our present categorial programs and required a brand new mind-set,” stated Zhang. “After cautious evaluation, the one merger state of affairs that made sense was that of a white dwarf and neutron star.”

UNLV doctoral pupil Shunke Ai and a pupil from Nanjing College collaborated to develop an in depth mannequin to interpret the peculiar kilonova signature noticed by GRB 211211A. Ai discovered that if a WD-NS merger leaves behind a quickly spinning neutron star, referred to as a magnetar, the extra power injection from the magnetar mixed with the nuclear response power from the fabric thrown through the burst can account for the kilonova emission noticed for GRB 211211A.

The research, “A long-duration gamma-ray burst with a peculiar origin“, appeared Dec. 7 within the journal Nature. The paper contains 10 co-authors from 4 establishments, with UNLV and Nanjing College being the lead establishments. Printed in the identical difficulty are three parallel papers that report the detection of the kilonova. This paper focuses on the peculiar gamma-ray emission itself and proposes the WD-NS merger mannequin to interpret the information.