In addition to difficult long-established beliefs about for how long GRBs are formed, the brand-new discovery also causes brand-new insights into the mysterious development of the heaviest elements in the universe.
The research study was published on December 7 in the journal Nature.
“Its gamma rays resemble those of bursts produced by the collapse of massive stars. Offered that all other verified neutron star mergers we have observed have actually been accompanied by bursts lasting less than two seconds, we had every factor to expect this 50-second GRB was produced by the collapse of an enormous star.
” When we followed this long gamma-ray burst, we expected it would lead to evidence of a massive star collapse,” said Northwesterns Wen-fai Fong, a senior author on the study. When I went into the field 15 years earlier, it was set in stone that long gamma-ray bursts come from huge star collapses.
Fong is an assistant teacher of physics and astronomy in Northwesterns Weinberg College of Arts and Sciences and a crucial member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). Rastinejad, a Ph.D. trainee in astronomy and member of Fongs research study group, is the papers first author.
Long division.
The brightest and most energetic explosions given that the Big Bang, GRBs are divided into two classes. GRBs with durations less than 2 seconds are thought about brief GRBs. If a GRB is longer than 2 seconds, then its thought about a long GRB. Researchers formerly thought that GRBs on either side of the dividing line must have different origins.
In December 2021, the Neil Gehrels Swift Observatorys Burst Alert Telescope and the Fermi Gamma-ray Space Telescope identified a brilliant burst of gamma-ray light, named GRB211211A. At simply over 50 seconds long, GRB211211A at first didnt seem anything special. Located about 1.1 billion light-years away– which, believe it or not, is relatively close to Earth– the astrophysicists chose to study this “nearby” occasion in detail, utilizing a multitude of telescopes that could observe throughout the electro-magnetic spectrum.
” It was cloudy there, however the telescope operators understood how essential this burst found a gap and was in between the clouds to take our images.”.
— Jillian Rastinejad, Ph.D. candidate in astronomy.
To image the event with near-infrared wavelengths, the group quickly initiated imaging with the Gemini Observatory in Hawaii. After two days of observing with Gemini, Rastinejad worried that she would be unable to get a clear view.
” The weather condition was worsening in Hawaii, and we were so dissatisfied because we were beginning to uncover tips that this burst was unlike anything we had seen prior to,” she said. “Luckily, Northwestern provides us with remote access to the MMT Observatory in Arizona, and an ideal instrument was being placed on that telescope the next day. It was cloudy there, but the telescope operators understood how essential this burst was and discovered a space between the clouds to take our images. It was so exciting however demanding to get those images in real time.”.
Telltale sign of a kilonova.
After examining the near-infrared images, the group identified an extremely faint object that quickly faded. Supernovae do not fade as rapidly and are much brighter, so the team recognized it found something unanticipated that was previously believed difficult.
” There are a lot of objects in our night sky that fade quickly,” Fong said. “We image a source in different filters to get color details, which assists us figure out the sources identity. In this case, red color dominated, and bluer colors faded faster. This color advancement is a telltale signature of a kilonova, and kilonovae can only come from neutron star mergers.”.
Because neutron stars are tidy, compact objects, scientists formerly thought neutron stars did not contain enough product to power a long-duration GRB. As the passing away star collapses, its product falls inward to feed a recently formed black hole.
” When you put two neutron stars together, theres not really much mass there,” Fong discussed. “A little bit of mass accretes and after that powers a very short-duration burst. When it comes to massive star collapses, which generally power longer gamma-ray bursts, there is a longer feeding time.”.
Altering the search.
The event wasnt the only strange part of the research study. The GRBs host galaxy likewise is quite curious. Called SDSS J140910.47 +275320.8, the host galaxy is star-forming and young, nearly exactly opposite of the only other known local universe host of a neutron star merger occasion: GW170817s host galaxy NGC4993. To evaluate the host galaxy, the group utilized data from the W.M. Keck Observatory, to which Northwestern has special remote access.
” After the detection of GW170817 and its association with a huge, red-and-dead host galaxy, numerous astronomers presumed that hosts of neutron star mergers in the near universe would look similar to NGC4993,” stated Anya Nugent, a Northwestern Ph.D. student in astronomy and research study co-author. “But this galaxy is relatively young, actively star forming and not really that massive.
It likewise changes how astrophysicists might approach the look for heavy aspects, such as platinum and gold. Researchers have been able to study the huge factories that produce lighter components, such as helium, silicon, and carbon, astrophysicists presume that supernova explosions and neutron star mergers produce the heaviest components. Clear signatures of their production, however, are seldom observed.
” Kilonovae are powered by the radioactive decay of some of the heaviest elements in deep space,” Rastinejad said. “But kilonovae are very hard to observe and fade extremely quickly. Now, we understand we can likewise utilize some long gamma-ray bursts to search for more kilonovae.”.
Now that the James Webb Space Telescope (JWST) is running, astrophysicists will have the ability to try to find more clues within kilonovae. It can find specific elements given off from the item because the JWST is capable of recording images and spectra of astronomical items. Utilizing the Webb, astrophysicists finally might acquire direct observational evidence of heavy components development.
” Unfortunately, even the very best ground-based telescopes are not delicate adequate to carry out spectroscopy,” Rastinejad stated. “With the JWST, we could have obtained a spectrum of the kilonova. Those spectral lines supply direct proof that you have spotted the heaviest elements.”.
For more on this research study, read Colossal Explosion Challenges Our Understanding of Gamma-Ray Bursts.
Referral: “A kilonova following a long-duration gamma-ray burst at 350 Mpc” by Jillian C. Rastinejad, Benjamin P. Gompertz, Andrew J. Levan, Wen-fai Fong, Matt Nicholl, Gavin P. Lamb, Daniele B. Malesani, Anya E. Nugent, Samantha R. Oates, Nial R. Tanvir, Antonio de Ugarte Postigo, Charles D. Kilpatrick, Christopher J. Moore, Brian D. Metzger, Maria Edvige Ravasio, Andrea Rossi, Genevieve Schroeder, Jacob Jencson, David J. Sand, Nathan Smith, José Feliciano Agüí Fernández, Edo Berger, Peter K. Blanchard, Ryan Chornock, Bethany E. Cobb, Massimiliano De Pasquale, Johan P. U. Fynbo, Luca Izzo, D. Alexander Kann, Tanmoy Laskar, Ester Marini, Kerry Paterson, Alicia Rouco Escorial, Huei M. Sears and Christina C. Thöne, 7 December 2022, Nature.DOI: 10.1038/ s41586-022-05390-w.
The study was supported by the National Science Foundation (grant numbers AST-1814782, AST-1909358, and AST-2047919), the David and Lucile Packard Foundation, the European Research Council, NASA, the Alfred P. Sloan Foundation and the Research Corporation for Scientific Advancement.
Provided that all other verified neutron star mergers we have actually observed have been accompanied by bursts lasting less than two seconds, we had every factor to expect this 50-second GRB was produced by the collapse of an enormous star.” When we followed this long gamma-ray burst, we expected it would lead to proof of a huge star collapse,” stated Northwesterns Wen-fai Fong, a senior author on the study. When I entered the field 15 years back, it was set in stone that long gamma-ray bursts come from enormous star collapses. Because neutron stars are clean, compact things, researchers previously thought neutron stars did not contain sufficient product to power a long-duration GRB. In the case of massive star collapses, which traditionally power longer gamma-ray bursts, there is a longer feeding time.”.
Artists impression of GRB 211211A. The kilonova and gamma-ray burst is on the. The blue color represents product squeezed along the poles, while the red colors suggest material ejected by the 2 inspiralling neutron stars that is now swirling around the merged object. A disk of ejecta discharged after the merger, hidden behind the red and blue ejecta, is displayed in purple. A fast jet (displayed in yellow) of product punches through the kilonova cloud. The event occurred roughly 8 kiloparsecs from its host galaxy (left). Credit: Aaron M. Geller/Northwestern/CIERA and IT Research Computing Services
Long Gamma-Ray Bursts Can Be Generated by Neutron Star Mergers
For almost 20 years, astrophysicists have actually thought that long gamma-ray bursts (GRBs) resulted entirely from the collapse of enormous stars. Now, a brand-new study upends that long-accepted and long-established belief..
Led by Northwestern University, a team of astrophysicists has actually revealed new evidence that at least some long GRBs can arise from neutron star mergers, which were formerly thought to produce only short GRBs.
After discovering a 50-second-long GRB in December 2021, the group started looking for the long GRBs afterglow, a fast-fading and extremely luminescent burst of light that frequently precedes a supernova. But, instead, they revealed proof of a kilonova, an uncommon occasion that only happens after the merger of a neutron star with another compact item (either another neutron star or a great void).
