Explosive neutron star merger captured for the first time in millimeter light
Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) – an international observatory partnered by the US National Science Foundation’s National Radio Astronomy Observatory (NRAO) – have recorded the first millimeter-wavelength light from a fiery explosion caused by the fusion of a neutron star with another star. The team also confirmed that this flash of light is one of the most energetic short-lived gamma-ray bursts ever observed, leaving behind one of the brightest afterglows ever recorded. The results of the study will be published in an upcoming issue of The astrophysical diary letters.
Gamma-ray bursts (GRBs) are the brightest and most energetic explosions in the universe, which can radiate more energy in a matter of seconds than our sun will radiate during its entire life. GRB 211106A belongs to a GRB subclass known as short-lived gamma-ray bursts. These explosions — which scientists believe are responsible for creating the heaviest elements in the universe, such as platinum and gold — result from the catastrophic merger of binary systems containing a neutron star. “These mergers happen because of gravitational wave radiation that removes energy from the orbit of the binaries, causing the stars to spiral toward each other,” said Tanmoy Laskar, who will soon be working as an assistant professor of physics and astronomy at the University of Utah. “The resulting explosion is accompanied by jets that move almost at the speed of light. When one of these jets is aimed at Earth, we perceive a short pulse of gamma rays or a short-lived GRB.”
A short-lived GRB usually lasts only a few tenths of a second. Scientists then look for an afterglow, an emission of light caused by the interaction of the jets with surrounding gas. Even still, they are hard to detect; only half a dozen short-lived GRBs have been detected at radio wavelengths, and so far none had been detected in millimeter wavelengths. Laskar, who led the research as an Excellence Fellow at Radboud University in the Netherlands, said the difficulty is the immense distance to GRBs and the technological capabilities of telescopes. “Short-lived grab afterglows are very luminous and energetic. But these explosions take place in distant galaxies, which means that their light can be quite dim for our telescopes on Earth. Before ALMA, millimeter telescopes were not sensitive enough to detect these afterglows.” .”
At about 20 billion light-years from Earth, GRB 211106A is no exception. The light from this short-lived gamma-ray burst was so dim that although early X-ray observations with NASA’s Neil Gehrel’s Swift Observatory spotted the explosion, the host galaxy at that wavelength was undetectable and scientists couldn’t pinpoint exactly where the explosion came from. “Afterglow light is essential for figuring out which galaxy an eruption is from and for learning more about the eruption itself. Initially, when only the X-ray counterpart was discovered, astronomers thought that this outburst could have come from a nearby galaxy.” Laskar said, adding that a significant amount of dust in the area also obscured the object from detection in optical observations with the Hubble Space Telescope.
Each wavelength added a new dimension to scientists’ understanding of the GRB, and the millimeter in particular was critical to uncovering the truth about the burst. “The Hubble observations revealed an unchanging field of galaxies. ALMA’s unparalleled sensitivity allowed us to more accurately determine the location of the GRB in that field, and it turned out to be in another faint galaxy, which is further away. in turn, means this short-lived gamma-ray burst is even more powerful than we first thought, making it one of the most luminous and energetic ever,” says Laskar.
Wen-fai Fong, an assistant professor of physics and astronomy at Northwestern University, added: “This brief gamma-ray burst was the first time we tried to observe such an event with ALMA. It was spectacular to see this event so bright. After many years of observing these eruptions, this surprising discovery opens up a new field of study, as it motivates us to observe many more of these eruptions with ALMA and other telescope arrays, in the future.”
Joe Pesce, National Science Foundation Program Officer for NRAO/ALMA said: “These observations are fantastic on many levels. They provide more information to help us understand the puzzling gamma-ray bursts (and neutron star astrophysics in general), and show how important and complementary multi-wavelength observations with telescopes in space and on the ground are for understanding astrophysical phenomena.”
And there’s still a lot of work to be done across multiple wavelengths, both with new GRBs and with GRB 211106A, which could uncover additional surprises about these bursts. “The study of short-lived GRBs requires the rapid coordination of telescopes around the world and in space, operating at all wavelengths,” said Edo Berger, a professor of astronomy at Harvard University.
“In the case of GRB 211106A, we used some of the most powerful telescopes available: ALMA, the National Science Foundation’s Karl G. Jansky Very Large Array (VLA), NASA’s Chandra X-ray Observatory, and the Hubble Now operational James Webb Space Telescope (JWST), and future 20-40 meter optical and radio telescopes such as the next generation VLA (ngVLA), we will be able to get a complete picture of these catastrophic events and they to study at unprecedented distances.”
Laskar added: “With JWST we can now take a spectrum of the host galaxy and easily know the distance, and in the future we can also use JWST to capture infrared afterglows and study their chemical composition. With ngVLA we will be able to to study the geometric structure of the afterglow and star-forming fuel in their host environments in unprecedented detail. I am excited about these upcoming discoveries in our field.”
Hawaii telescopes help uncover the origin of castaway gamma-ray bursts
Tanmoy Laskar et al, The First Short GRB Millimeter Afterglow: The Wide-Angled Jet of the Extremely Energetic SGRB 211106A. arXiv:2205.03419v2 [astro-ph.HE], arxiv.org/abs/2205.03419
Quote: Explosive Fusion of Neutron Stars Captured in Millimeter Light for the First Time (2022, Aug. 3), retrieved Aug. 3, 2022 from https://phys.org/news/2022-08-explosive-neutron-star-merger-captured.html
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