The distant neutron-star merger ejected one of the most powerful short gamma-ray bursts (GRBs) ever observed, according to new observations by ALMA, the Atacama Large Millimeter/submillimeter Array in Chile.
Neutron stars are super-dense stellar cores that are left over after massive stars explode, and when, say, two neutron stars collide, the result is a dramatic explosion, the light of which is a . is called kilonova, merger continues gravitational waves and a brief burst of gamma-ray radiation in two tight jets shooting in opposite directions into space.
On 6 November 2021, a brief gamma-ray burst was detected by the European Space Agency’s Integral X-ray and Gamma-ray Observatory, which sent an immediate alert that triggered NASA acute satellites, among others, to follow. The explosion, which was cataloged as GRB 211106A, lasted less than two seconds, but the subsequent glow from the kilonova lasted longer as the jet of particles released by the merger excited the surrounding gas.
“This short gamma-ray burst was the first time we tried to observe such an event with ALMA,” said Wen-Fei Fong, an astronomer at Northwestern University in Illinois. Statement, “The afterglow is very hard to come by for short bursts, so it was wonderful to capture this glow with such a glow.”
Detecting the post-merger flashes in the millimeter-wavelength light that ALMA is designed to give astronomers an advantage in understanding these Titanic explosions.
“Millimetre wavelengths can tell us about the density of the atmosphere around GRBs,” Northwestern University’s Genevieve Schroeder said in the same statement. “And, when combined with X-rays, [the millimeter-wave light] can tell us about the actual energy of the explosion.”
Shockwaves intensify as jets of GRBs, which travel at nearly the speed of light, collide with surrounding gas electrons, The energy of radiation from those electrons reaches millimeter wavelengths, and can therefore tell astronomers about the total energy of the explosion.
almaK measurements show that GRB 211106A released a total energy of between 2 x 10^50 ergs and 6 x 10^51 ergs, placing it among the most powerful miniature GRBs ever discovered. (One erg is equal to 10^–7 joules; for comparison, Sun releases only 3.8 x 10^33 erg per second.)
This is particularly impressive given that GRB 211106a was so bright, relatively speaking, because the merger occurred between 6.3 and 9.1 billion years ago, and the galaxy in which the merger took place is now about 20 billion light—from Earth—due to cosmic expansion. Years away. At this distance, the gravitational waves released by the merger were too weak to be detected.
Another advantage of observing with ALMA is that the afterglow at millimeter wavelengths lasts longer than with X-rays. This gives astronomers more time to study the GRB jet, which begins as a narrow stream, then slowly opens up like a laser pointer that creates a larger spot on the wall than the base of the laser. Is.
Fong and Schroeder’s team calculated the jet’s starting angle as 16 degrees, the widest measurement ever taken for a small GRB. This is important because we only see a GRB when the jet is pointed at us, so the wider the jet, the more chances we have of seeing it.
And constraints matter: Astronomers calculate the rate of neutron-star mergers in the universe based on how many small GRBs we see and estimate the starting angles of their jets. If the more small GRBs had jets with wider opening angles, scientists would have estimated how many neutron-star mergers are occurring.
The rate at which neutron stars merge isn’t just an astronomical curiosity—it has an effect on cosmic chemistry. The conditions during neutron-star mergers are so intense that some of the universe’s heaviest and most precious element, such as gold, platinum and silver, are forged from these collisions. Indeed, scientists have estimated that a neutron-star merger could produce 3 to 13 Earth masses of gold. So cosmic abundance The amount of such elements depends heavily on the rate at which neutron-star mergers occur.
While the collision is a function of cosmic alchemy, enriching the surrounding region with nuclear treasures, the discovery has provided astronomers with a new field for studying miniature GRBs and their subsequent study. “After a decade of observing miniature GRBs, it’s really amazing to see the power of using these new technologies to uncover amazing gifts from the universe,” Fong said.
A paper describing the findings is due to be published in an upcoming issue of the Astrophysical Journal Letters; One preprint version Posted on Monday (August 1).