Unexpected kilonova discovery: a massive explosion that challenges our understanding of gamma-ray bursts

This artist’s impression shows a kilonova caused by the collision of two neutron stars. While studying the aftermath of a long gamma-ray burst (GRB), two independent teams of astronomers using an array of telescopes in space and on Earth, including the Gemini North telescope in Hawaii and the Gemini South telescope in Chile, made the discovery. The unexpected distinguishing features of a kilonova, the massive explosion caused by the collision of neutron stars. Credit: NOIRLab/NSF/AURA/J. da Silva/Spaceengine

The Gemini International Observatory uncovers surprising evidence of colliding neutron stars after investigating the effects of a gamma-ray burst.

While investigating the aftermath of a long gamma-ray burst (GRB), two independent teams of astronomers using an array of telescopes in space and on Earth have discovered the unexpected hallmarks of a kilonova. This is a massive explosion caused by the collision of neutron stars. The finding challenges the prevailing theory that long GRBs come exclusively from supernovae, the end-of-life explosions of massive stars.

Gamma ray bursts (GRBs) are the most energetic explosions in the universe. They come in two types, long and short. Long GRBs, lasting a few seconds to 1 minute, are formed when a star at least 10 times the mass of our Sun explodes as a supernova. Short GRBs, lasting less than two seconds, occur when two compact objects, such as two neutron stars or a neutron star and a black hole, collide to form a kilonova.

While observing the fallout from a long GRB detected in 2021, two independent teams of astronomers have found surprising signs of a neutron star merger rather than the expected signal of a supernova. This surprising result marks the first time that a kilonova has been associated with a long GRB and challenges our understanding of these powerful, massive explosions.

Gemini North and Hubble afterglow image, annotated GRB

This image of Gemini North, superimposed on an image taken with the Hubble Space Telescope, shows the kilonova’s near-infrared afterglow from a long GRB (GRB 211211A). The finding challenges the prevailing theory that long GRBs come exclusively from supernovae, the end-of-life explosions of massive stars. Credit: Gemini Observatory International/NOIRLab/NSF/AURA/M. Zamani. NASA/European Space Agency

The first team to announce the discovery was led by Jillian Rastingad, a Ph

Northwestern University
Founded in 1851, Northwestern University (NU) is a private research university based in Evanston, Illinois, United States. Northwestern is known for the McCormick School of Engineering and Applied Science, the Kellogg School of Management, the Feinberg School of Medicine, the Pritzker School of Law, the Pennine College of Music, and the Medill School of Journalism.

“data-gt-translate-attributes=”[{” attribute=””>Northwestern University. Rastinejad and her colleagues made this startling discovery with the help of the Gemini North telescope on Hawai‘i, part of the International Gemini Observatory, which is operated by NSF’s NOIRLab. The Gemini North observations revealed a telltale near-infrared afterglow at the precise location of the GRB, providing the first compelling evidence of a kilonova associated with this event.[1] The Rastinejad team immediately reported the discovery of Gemini in the Gamma-Ray Coordinate Network (GCN).

Astronomers around the world were first alerted to this explosion, called GRB 211211A, when a powerful flash of gamma rays was captured by

NASA
Founded in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States federal government that is the successor to the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aviation and space research. see it is “To discover and expand knowledge for the benefit of mankind.” its core values “Safety, integrity, teamwork, excellence and inclusion.”

“data-gt-translate-attributes=”[{” attribute=””>NASA’s Neil Gehrels Swift Observatory and Fermi Gamma-ray Space Telescope. Initial observations revealed that the GRB was uncommonly nearby, a mere one billion light-years from Earth.


An interview with Eleonora Troja, an astronomer at the University of Rome Tor Vergata, who has studied GRB afterglows using a series of observations, including the Gemini South telescope in Chile, and has independently concluded that the long GRB came from a kilonova.

Most GRBs originated in the distant, distant universe. Usually, these objects are so old and so far away that their light would have had to travel more than six billion years to reach Earth. Light from the farthest GRB ever recorded traveled for nearly 13 billion years before it was detected here on Earth.[2] The relative proximity of the newly discovered GRB has enabled astronomers to conduct remarkably detailed follow-up studies with a variety of ground-based and space-based telescopes.

“Typically, astronomers investigate short GRBs when looking for kilonovas,” Rastingad said. “We were drawn to this longer-duration burst because it was so close that we could study it in detail. Its gamma-rays were also similar to earlier, mysterious GRBs that did not have a long-distance supernova.”

A unique hallmark of a kilonova is its brightness at near-infrared wavelengths compared to its brightness in visible light. This difference in brightness is due to the heavy elements ejected by a kilonova, which effectively block visible light but allow longer-wavelength infrared light to pass through unimpeded. However, observing in the near infrared is technically challenging, and only a few telescopes on Earth, such as the Gemini twin telescopes, are sensitive enough to detect this kilonova at these wavelengths.


Northwestern University doctoral student Gillian Rastingad and colleagues used the Gemini North telescope to detect the near-infrared afterglow at the exact location of the GRB, providing the first convincing evidence of a kilonova associated with this event.

“Thanks to its sensitivity and our quick response, Gemini was the first to detect this kilonova in the near infrared, convincing us that we are observing neutron star mergers,” Rastengad said. “Gemini’s intelligent capabilities and diverse set of tools allow us to design a monitoring plan each night based on the results of the previous night, allowing us to make the most of every minute our target was visible.”

Another team, led by Tor Vergata University of Rome astronomer Eleonora Troja, independently studied afterglows using a different series of observations, including the Gemini South telescope in Chile,[3] It was independently concluded that the long GRB came from Kilonova.

“We were only able to observe this event because it was so close to us,” Troja said. “It is very rare that we observe such powerful explosions in our cosmic backyard, and each time we learn about the most extreme objects in the universe.”

The fact that two different teams of scientists working with independent data sets have come to the same conclusion about the kilonova nature of this GRB provides confidence in this interpretation.

“The kilonova explanation was so far removed from everything we know about long GRBs that we couldn’t believe our eyes and spent months testing all the other possibilities,” Troja said. “It was only after everything else was excluded that we realized that our decade-old model had to be revised.”

In addition to contributing to our understanding of kilonovae and GRBs, this discovery provides astronomers with a new way to study the composition of gold and other heavy elements in the universe. The harsh physical conditions in a kilonova produce heavy elements such as gold, platinum, and thorium. Astronomers can now pinpoint sites that create heavy elements by looking for the signature of a kilonova after a long-duration gamma-ray burst.

“This discovery is a clear reminder that the universe has never been fully explored,” Rastenjad said. “Astronomers often take it for granted that the origins of GRBs can be determined by how long the GRBs are, but this discovery shows us that there is still much to understand about these amazing events.”

“NSF congratulates the science teams on this exciting new discovery, which opens a new window on cosmic evolution,” said National Science Foundation Director Sethuraman Panchanathan. “Gemini Observatory International continues to provide robust and agile resources open to the entire science community through innovation and partnership.”

For more information on this research, see Hybrid merger event of neutron stars detected by an unusual gamma-ray burst.

Gemini International Observatory is operated by a partnership of six countries, including the United States through the National Science Foundation, Canada through the National Research Council of Canada, Chile through the National Research and Development Agency, Brazil through the Ministry of Science, Technology and Innovations, and Argentina through Through the Ministry of Science, Technology and Innovation, Korea through the Korea Institute of Astronomy and Astronomy. These participants and the University of Hawaii, which has regular access to Gemini, each maintain a Gemini National Office to support local users.

notes

  1. Rastenjad and her colleagues made initial follow-up observations of the outburst using the Scandinavian Optical Telescope. After the critical Gemini North observations, they continued their observations of the vanishing kilonova using the Karl G. Gran Telescope Array, Canary Islands, and NASA/ESA
    Hubble Space Telescope
    The Hubble Space Telescope (often referred to as Hubble or HST) is one of NASA’s largest observatories and was launched into low Earth orbit in 1990. It is one of the largest and most versatile space telescopes in use and features a mirror with a diameter of 2.4 meters. Four major instruments are observed in the ultraviolet, visible, and near-infrared regions of the electromagnetic spectrum. It is named after astronomer Edwin Hubble.

    “data-gt-translate-attributes=”[{” attribute=””>Hubble Space Telescope.

  2. Light that has traveled nearly 13 billion years to reach Earth would have a redshift (z) of about 7. Due to the accelerating expansion of the Universe, that would roughly equate to a distance of 24.5 billion light-years today. When talking about large redshifts, those greater than 1, and cosmically distant objects, it is more accurate to state how many billions of years the light has traveled rather than a distance in light-years.
  3. Troja and her colleagues initially observed the afterglow of this event with the Devasthal Optical Telescope, the Multicolor Imaging Telescopes for Survey and Monstrous Explosions, and the Calar Alto Observatory. They obtained observations of the host galaxy with the NASA/ESA Hubble Space Telescope.

References:

“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

“A nearby long gamma-ray burst from a merger of compact objects” by E. Troja, C. L. Fryer, B. O’Connor, G. Ryan, S. Dichiara, A. Kumar, N. Ito, R. Gupta, R. Wollaeger, J. P. Norris, N. Kawai, N. Butler, A. Aryan, K. Misra, R. Hosokawa, K. L. Murata, M. Niwano, S. B. Pandey, A. Kutyrev, H. J. van Eerten, E. A. Chase, Y.-D. Hu, M. D. Caballero-Garcia, A. J. Castro-Tira, 7 December 2022, Nature.
DOI: 10.1038/s41586-022-05327-3


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