In October 2022, a world crew of researchers, together with Northwestern College astrophysicists, noticed the brightest gamma-ray burst (GRB) ever recorded, GRB 221009A.
Now, a Northwestern-led crew has confirmed that the phenomenon chargeable for the historic burst — dubbed the B.O.A.T. (“brightest of all time”) — is the collapse and subsequent explosion of a large star. The crew found the explosion, or supernova, utilizing NASA’s James Webb Area Telescope (JWST).
Whereas this discovery solves one thriller, one other thriller deepens.
The researchers speculated that proof of heavy parts, reminiscent of platinum and gold, would possibly reside inside the newly uncovered supernova. The in depth search, nevertheless, didn’t discover the signature that accompanies such parts. The origin of heavy parts within the universe continues to stay as considered one of astronomy’s greatest open questions.
The analysis can be printed on Friday (April 12) within the journal Nature Astronomy.
“After we confirmed that the GRB was generated by the collapse of a large star, that gave us the chance to check a speculation for a way a few of the heaviest parts within the universe are shaped,” mentioned Northwestern’s Peter Blanchard, who led the examine. “We didn’t see signatures of those heavy parts, suggesting that extraordinarily energetic GRBs just like the B.O.A.T. don’t produce these parts. That does not imply that every one GRBs don’t produce them, however it’s a key piece of knowledge as we proceed to grasp the place these heavy parts come from. Future observations with JWST will decide if the B.O.A.T.’s ‘regular’ cousins produce these parts.”
Blanchard is a postdoctoral fellow at Northwestern’s Middle for Interdisciplinary Exploration and Analysis in Astrophysics (CIERA), the place he research superluminous supernovae and GRBs. The examine consists of co-authors from the Middle for Astrophysics | Harvard & Smithsonian; College of Utah; Penn State; College of California, Berkeley; Radbound College within the Netherlands; Area Telescope Science Institute; College of Arizona/Steward Observatory; College of California, Santa Barbara; Columbia College; Flatiron Institute; College of Greifswald and the College of Guelph.
Beginning of the B.O.A.T.
When its gentle washed over Earth on Oct. 9, 2022, the B.O.A.T. was so shiny that it saturated a lot of the world’s gamma-ray detectors. The highly effective explosion occurred roughly 2.4 billion light-years away from Earth, within the path of the constellation Sagitta and lasted a couple of hundred seconds in period. As astronomers scrambled to watch the origin of this extremely shiny phenomenon, they have been instantly hit with a way of awe.
“So long as we’ve been in a position to detect GRBs, there isn’t any query that this GRB is the brightest we’ve ever witnessed by an element of 10 or extra,” Wen-fai Fong, an affiliate professor of physics and astronomy at Northwestern’s Weinberg School of Arts and Sciences and member of CIERA, mentioned on the time.
“The occasion produced a few of the highest-energy photons ever recorded by satellites designed to detect gamma rays,” Blanchard mentioned. “This was an occasion that Earth sees solely as soon as each 10,000 years. We’re lucky to dwell in a time when we’ve the expertise to detect these bursts occurring throughout the universe. It is so thrilling to watch such a uncommon astronomical phenomenon because the B.O.A.T. and work to grasp the physics behind this distinctive occasion.”
A ‘regular’ supernova
Quite than observe the occasion instantly, Blanchard, his shut collaborator Ashley Villar of Harvard College and their crew needed to view the GRB throughout its later phases. About six months after the GRB was initially detected, Blanchard used the JWST to look at its aftermath.
“The GRB was so shiny that it obscured any potential supernova signature within the first weeks and months after the burst,” Blanchard mentioned. “At these instances, the so-called afterglow of the GRB was just like the headlights of a automobile coming straight at you, stopping you from seeing the automobile itself. So, we needed to await it to fade considerably to present us an opportunity of seeing the supernova.”
Blanchard used the JWST’s Close to Infrared Spectrograph to watch the item’s gentle at infrared wavelengths. That is when he noticed the attribute signature of parts like calcium and oxygen usually discovered inside a supernova. Surprisingly, it wasn’t exceptionally shiny — just like the extremely shiny GRB that it accompanied.
“It is not any brighter than earlier supernovae,” Blanchard mentioned. “It seems pretty regular within the context of different supernovae related to much less energetic GRBs. You would possibly count on that the identical collapsing star producing a really energetic and shiny GRB would additionally produce a really energetic and shiny supernova. However it seems that is not the case. We’ve this extraordinarily luminous GRB, however a standard supernova.”
Lacking: Heavy parts
After confirming — for the primary time — the presence of the supernova, Blanchard and his collaborators then looked for proof of heavy parts inside it. At present, astrophysicists have an incomplete image of all of the mechanisms within the universe that may produce parts heavier than iron.
The first mechanism for producing heavy parts, the fast neutron seize course of, requires a excessive focus of neutrons. To date, astrophysicists have solely confirmed the manufacturing of heavy parts by way of this course of within the merger of two neutron stars, a collision detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2017. However scientists say there should be different methods to provide these elusive supplies. There are just too many heavy parts within the universe and too few neutron-star mergers.
“There may be probably one other supply,” Blanchard mentioned. “It takes a really very long time for binary neutron stars to merge. Two stars in a binary system first should explode to go away behind neutron stars. Then, it could actually take billions and billions of years for the 2 neutron stars to slowly get nearer and nearer and eventually merge. However observations of very previous stars point out that elements of the universe have been enriched with heavy metals earlier than most binary neutron stars would have had time to merge. That is pointing us to an alternate channel.”
Astrophysicists have hypothesized that heavy parts additionally may be produced by the collapse of a quickly spinning, huge star — the precise kind of star that generated the B.O.A.T. Utilizing the infrared spectrum obtained by the JWST, Blanchard studied the internal layers of the supernova, the place the heavy parts must be shaped.
“The exploded materials of the star is opaque at early instances, so you may solely see the outer layers,” Blanchard mentioned. “However as soon as it expands and cools, it turns into clear. Then you may see the photons coming from the internal layer of the supernova.”
“Furthermore, completely different parts soak up and emit photons at completely different wavelengths, relying on their atomic construction, giving every component a singular spectral signature,” Blanchard defined. “Subsequently, an object’s spectrum can inform us what parts are current. Upon inspecting the B.O.A.T.’s spectrum, we didn’t see any signature of heavy parts, suggesting excessive occasions like GRB 221009A should not major sources. That is essential data as we proceed to attempt to pin down the place the heaviest parts are shaped.”
Why so shiny?
To tease aside the sunshine of the supernova from that of the intense afterglow that got here earlier than it, the researchers paired the JWST information with observations from the Atacama Massive Millimeter/Submillimeter Array (ALMA) in Chile.
“Even a number of months after the burst was found, the afterglow was shiny sufficient to contribute loads of gentle within the JWST spectra,” mentioned Tanmoy Laskar, an assistant professor of physics and astronomy on the College of Utah and a co-author on the examine. “Combining information from the 2 telescopes helped us measure precisely how shiny the afterglow was on the time of our JWST observations and permit us to fastidiously extract the spectrum of the supernova.”
Though astrophysicists have but to uncover how a “regular” supernova and a record-breaking GRB have been produced by the identical collapsed star, Laskar mentioned it may be associated to the form and construction of the relativistic jets. When quickly spinning, huge stars collapse into black holes, they produce jets of fabric that launch at charges near the velocity of sunshine. If these jets are slim, they produce a extra targeted — and brighter — beam of sunshine.
“It is like focusing a flashlight’s beam right into a slim column, versus a broad beam that washes throughout an entire wall,” Laskar mentioned. “The truth is, this was one of many narrowest jets seen for a gamma-ray burst to this point, which supplies us a touch as to why the afterglow appeared as shiny because it did. There could also be different components accountable as properly, a query that researchers can be finding out for years to come back.”
Further clues additionally might come from future research of the galaxy through which the B.O.A.T. occurred. “Along with a spectrum of the B.O.A.T. itself, we additionally obtained a spectrum of its ‘host’ galaxy,” Blanchard mentioned. “The spectrum reveals indicators of intense star formation, hinting that the start setting of the unique star could also be completely different than earlier occasions.”
Staff member Yijia Li, a graduate scholar at Penn State, modeled the spectrum of the galaxy, discovering that the B.O.A.T.’s host galaxy has the bottom metallicity, a measure of the abundance of parts heavier than hydrogen and helium, of all earlier GRB host galaxies. “That is one other distinctive facet of the B.O.A.T. which will assist clarify its properties,” Li mentioned.
The examine, “JWST detection of a supernova related to GRB 221009A with out an r-process signature,” was supported by NASA (award quantity JWST-GO-2784) and the Nationwide Science Basis (award numbers AST-2108676 and AST-2002577). This work relies on observations made with the NASA/ESA/CSA James Webb Area Telescope.
