On Dec. 11, 2021, NASA’s Neil Gehrels Swift Observatory and Fermi Gamma-ray House Telescope detected a blast of high-energy mild from the outskirts of a galaxy round 1 billion light-years away. The occasion has rattled scientists’ understanding of gamma-ray bursts (GRBs), essentially the most highly effective occasions within the universe.
For the previous few many years, astronomers have typically divided GRBs into two classes. Lengthy bursts emit gamma rays for 2 seconds or extra and originate from the formation of dense objects like black holes within the facilities of huge collapsing stars. Brief bursts emit gamma rays for lower than two seconds and are attributable to mergers of dense objects like neutron stars. Scientists generally observe quick bursts with a following flare of seen and infrared mild known as a kilonova.
“This burst, named GRB 211211A, was paradigm-shifting as it’s the first long-duration gamma-ray burst traced to a neutron star merger origin,” mentioned Jillian Rastinejad, a graduate scholar at Northwestern College in Evanston, Illinois, who led one staff that studied the burst. “The high-energy burst lasted a couple of minute, and our follow-up observations led to the identification of a kilonova. This discovery has deep implications for a way the universe’s heavy components got here to be.”
A traditional quick gamma-ray burst begins with two orbiting neutron stars, the crushed remnants of huge stars that exploded as supernovae. As the celebs circle ever nearer, they strip neutron-rich materials from one another. Additionally they generate gravitational waves, or ripples in space-time — though none had been detected from this occasion.
Finally the neutron stars collide and merge, making a cloud of sizzling particles emitting mild throughout a number of wavelengths. Scientists hypothesize that jets of high-speed particles, launched by the merger, produce the preliminary gamma-ray flare earlier than they collide with the wreckage. Warmth generated by the radioactive decay of components within the neutron-rich particles probably creates the kilonova’s seen and infrared mild. This decay ends in the manufacturing of heavy components like gold and platinum.
“A few years in the past, Neil Gehrels, an astrophysicist and Swift’s namesake, steered that neutron star mergers may produce some lengthy bursts,” mentioned Eleonora Troja, an astrophysicist on the College of Rome who led one other staff that studied the burst. “The kilonova we noticed is the proof that connects mergers to those long-duration occasions, forcing us to rethink how black holes are fashioned.”
Fermi and Swift detected the burst concurrently, and Swift was capable of quickly establish its location within the constellation Boötes, enabling different services to shortly reply with follow-up observations. Their observations have supplied the earliest look but on the first phases of a kilonova.
Many analysis teams have delved into the observations collected by Swift, Fermi, the Hubble House Telescope, and others. Some have steered the burst’s oddities might be defined by the merger of a neutron star with one other huge object, like a black gap. The occasion was additionally comparatively close by, by gamma-ray burst requirements, which can have allowed telescopes to catch the kilonova’s fainter mild. Maybe some distant lengthy bursts may additionally produce kilonovae, however we’ve not been capable of see them.
The sunshine following the burst, known as the afterglow emission, additionally exhibited uncommon options. Fermi detected high-energy gamma rays beginning 1.5 hours post-burst and lasting greater than 2 hours. These gamma rays reached energies of as much as 1 billion electron volts. (Seen mild’s power measures between about 2 and three electron volts, for comparability.)
“That is the primary time we have seen such an extra of high-energy gamma rays within the afterglow of a merger occasion. Usually that emission decreases over time,” mentioned Alessio Mei, a doctoral candidate on the Gran Sasso Science Institute in L’Aquila, Italy, who led a bunch that studied the info. “It is doable these high-energy gamma rays come from collisions between seen mild from the kilonova and electrons in particle jets. The jets might be weakening ones from the unique explosion or new ones powered by the ensuing black gap or magnetar.”
Scientists assume neutron star mergers are a significant supply of the universe’s heavy components. They primarily based their estimates on the speed of quick bursts thought to happen throughout the cosmos. Now they will have to issue lengthy bursts into their calculations as properly.
A staff led by Benjamin Gompertz, an astrophysicist on the College of Birmingham in the UK, appeared on the total high-energy mild curve, or the evolution of the occasion’s brightness over time. The scientists famous options that may present a key for figuring out related incidents — lengthy bursts from mergers — sooner or later, even ones which are dimmer or extra distant. The extra astronomers can discover, the extra they’ll refine their understanding of this new class of phenomena.
On Dec. 7, 2022, papers led by Rastinejad, Troja, and Mei had been printed within the scientific journal Nature, and a paper led by Gompertz was printed in Nature Astronomy.
“This consequence underscores the significance of our missions working collectively and with others to supply multiwavelength comply with up of those sorts of phenomenon,” mentioned Regina Caputo, Swift undertaking scientist, at NASA’s Goddard House Flight Heart in Greenbelt, Maryland. “Related coordinated efforts have hinted that some supernovae may produce quick bursts, however this occasion is the ultimate nail within the coffin for the straightforward dichotomy we have used for years. You by no means know while you may discover one thing shocking.”
NASA’s Goddard House Flight Heart manages the Swift and Fermi missions.
Swift is a collaboration with Penn State, the Los Alamos Nationwide Laboratory in New Mexico, and Northrop Grumman House Programs in Dulles, Virginia, with essential contributions from companions in the UK and Italy.
Fermi is a collaboration with the U.S. Division of Power, with essential contributions from companions in France, Germany, Italy, Japan, Sweden, and america.
The Hubble House Telescope is a undertaking of worldwide cooperation between NASA and ESA (European House Company). Goddard manages the telescope. The House Telescope Science Institute (STScI) in Baltimore conducts science operations. STScI is operated for NASA by the Affiliation of Universities for Analysis in Astronomy, in Washington, D.C.
