November 29, 2023

Not Black Holes: Astronomers May Need To Rethink How Gamma-Ray Bursts Are Formed

An artists impression of a gamma-ray burst powered by a neutron star. Credit: Nuria Jordana-Mitjans
According to current research study from the University of Bath in the UK, newborn supramassive stars, instead of great voids, may be the cause of gamma-ray bursts.
Satellites orbiting Earth have actually detected Gamma-ray bursts (GRBs) as luminescent flashes of incredibly energetic gamma-ray radiation that last from milliseconds to hundreds of seconds. These catastrophic blasts happen in remote galaxies billions of light-years away from Earth.
A kind of GRB called a short-duration GRB is produced when two neutron stars clash. These ultra-dense stars, which have the mass of our Sun compressed into a size smaller sized than a city, create ripples in space-time called gravitational waves simply before activating a GRB in their final minutes.

Previously, space scientists have largely agreed that the engine powering such energetic and brief bursts need to always originate from a newly formed great void (an area of space-time where gravity is so strong that absolutely nothing, not even light, can escape from it). New research study by a worldwide team of astrophysicists, led by Dr. Nuria Jordana-Mitjans at the University of Bath in the UK, is challenging this scientific orthodoxy.
According to the research studys findings, some short-duration GRBs are set off by the birth of a supramassive star (otherwise called a neutron star remnant) not a black hole.
Dr. Jordana-Mitjans stated: “Such findings are crucial as they confirm that newborn neutron stars can power some short-duration GRBs and the intense emissions throughout the electro-magnetic spectrum that have actually been found accompanying them. This discovery may provide a brand-new way to locate neutron star mergers, and therefore gravitational waves emitters when were browsing the skies for signals.”
Contending theories
Much is learnt about short-duration GRBs. They begin life when two neutron stars, which have actually been spiraling ever better, constantly accelerating, lastly crash. And from the crash site, a jetted explosion releases the gamma-ray radiation that makes a GRB, followed by a longer-lived afterglow. A day later on, the radioactive product that was expelled in all directions during the explosion produced what researchers call a kilonova.
Precisely what stays after two neutron stars collide– the item of the crash– and as a result the power source that provides a GRB its amazing energy, has actually long been a matter of debate. Scientists might now be closer to solving this dispute, thanks to the findings of the Bath-led study.
Area scientists are split in between 2 theories. The very first theory has it that neutron stars combine to briefly form an incredibly enormous neutron star, just for this star to then collapse into a black hole in a portion of a 2nd. The second argues that the 2 neutron stars would lead to a less heavy neutron star with a higher life expectancy.
The concern that has been needling astrophysicists for years is this: are short-duration GRBs powered by a black hole or by the birth of a long-lived neutron star?
To date, a lot of astrophysicists have actually supported the black hole theory, concurring that to produce a GRB, it is required for the enormous neutron star to collapse practically immediately.
Electromagnetic signals
Astrophysicists discover neutron star collisions by measuring the electro-magnetic signals of the resultant GRBs. The signal stemming from a great void would be expected to differ from that originating from a neutron star remnant.
The electromagnetic signal from the GRB checked out for this study (called GRB 180618A) made it clear to Dr. Jordana-Mitjans and her partners that a neutron star remnant rather than a great void need to have generated this burst.
Elaborating, Dr. Jordana-Mitjans stated: “For the very first time, our observations highlight several signals from a surviving neutron star that lived for a minimum of one day after the death of the initial neutron star binary.”
Professor Carole Mundell, study co-author and teacher of Extragalactic Astronomy at Bath, where she holds the Hiroko Sherwin Chair in Extragalactic Astronomy, said: “We were delighted to catch the really early optical light from this brief gamma-ray burst– something that is still mostly impossible to do without using a robotic telescope. However when we examined our exquisite information, we were surprised to discover we couldnt explain it with the basic fast-collapse black hole model of GRBs.
” Our discovery opens new hope for upcoming sky studies with telescopes such as the Rubin Observatory LSST with which we may discover signals from numerous countless such long-lived neutron stars prior to they collapse to end up being black holes.”
Vanishing afterglow
What at first puzzled the scientists was that the optical light from the afterglow that followed GRB 180618A disappeared after just 35 minutes. Further analysis showed that the material responsible for such a short emission was broadening near to the speed of light due to some source of constant energy that was pushing it from behind.
What was more unexpected was that this emission had the imprint of a newborn, quickly spinning and extremely magnetized neutron star called a millisecond magnetar. The team discovered that the magnetar after GRB 180618A was reheating the leftover material of the crash as it was decreasing.
In GRB 180618A, the magnetar-powered optical emission was one-thousand times brighter than what was expected from a classical kilonova.
Recommendation: “A Short Gamma-Ray Burst from a Protomagnetar Remnant” by N. Jordana-Mitjans, C. G. Mundell, C. Guidorzi, R. J. Smith, E. Ramírez-Ruiz, B. D. Metzger, S. Kobayashi, A. Gomboc, I. A. Steele, M. Shrestha, M. Marongiu, A. Rossi and B. Rothberg, 10 November 2022, The Astronomical Journal.DOI: 10.3847/ 1538-4357/ ac972b.
The research study was funded by the Hiroko and Jim Sherwin Postgraduate Studentship..

Much is understood about short-duration GRBs. They start life when 2 neutron stars, which have actually been spiraling ever closer, continuously speeding up, lastly crash. And from the crash website, a jetted explosion launches the gamma-ray radiation that makes a GRB, followed by a longer-lived afterglow. The very first theory has it that neutron stars merge to briefly form an extremely massive neutron star, only for this star to then collapse into a black hole in a fraction of a second. The second argues that the two neutron stars would result in a less heavy neutron star with a greater life expectancy.