Artist’s impression of helium-rich material from a companion star accreting onto a white dwarf. Before the explosion, a large amount of material is ejected from the satellite. The research team hopes to clarify the connection between the emitted strong radio waves and this exposed material. Credit: Adam Makarenko/WM Keck Observatory
In the last issue of Nature, astronomers from Stockholm University reveal the origin of the thermonuclear supernova explosion. Strong helium emission lines and the first detection of such a supernova in radio waves indicate that the explosion a white dwarf the star had a helium-rich companion.
Stockholm University researchers have discovered the origin of a thermonuclear supernova traced to a helium-rich white dwarf companion star. This first detection of a supernova in radio waves sheds light on the nature and processes leading to Type Ia supernovae, which are crucial for measuring the expansion of the universe. The discovery helps resolve a long-standing question about the process leading to the explosion of a white dwarf star and the nature of its progenitor, identified here as a helium star that lost much of its material just before the white dwarf exploded.
Type Ia supernovae are important to astronomers because they are used to measure the expansion of the universe. However, the origin of these explosions remains an open question. Although the explosion was determined to be of a compact white dwarf star that somehow accreted too much matter from another star, the exact process and nature of the progenitor are unknown. The new discovery of supernova SN 2020eyj found that the companion star was a helium star that lost much of its material just before the white dwarf exploded.
Artist’s impression of a binary star system with a compact white dwarf star accreting matter from a helium-rich donor companion surrounded by dense and dusty circumstellar material. It was the interaction of the exploded star and the material left over from this companion that gave rise to the strong radio signal and visible helium lines in the optical spectra of SN 2020eyj. Credit: Adam Makarenko/WM Keck Observatory“After seeing the signs of a strong interaction with the material from the satellite, we tried to detect it in the radio emission as well,” explains Erik Kuhl, a postdoctoral fellow at the Department of Astronomy at Stockholm University and lead author of the report. “The radio detection is the first of a Type Ia supernova – something astronomers have been trying to do for decades.”
Supernova 2020eyj was detected by the Zwicky Transient Facility camera on Mount Palomar, where the Oscar Klein Center at Stockholm University is a member.
“The Northern Optical Telescope at La Palma was fundamental to the tracking of this supernova,” says Professor Jesper Sollerman from the Department of Astronomy and co-author of the paper.
“As well as spectra from the Large Keck Telescope in Hawaii, which immediately revealed the very unusual helium-dominated material around the exploded star.”
Erik Kuhl (middle) and Joel Johansson (left) are PhD students at the Oscar Klein Center at Stockholm University and lead authors of this paper together with Professor Jesper Sollerman (right) from the Department of Astronomy. Credit: Magnus Näslund
“This is clearly a very unusual type Ia supernova, but it is still related to those we use to measure the expansion of the universe,” adds Joel Johansson from the Department of Physics.
“While normal Type Ia supernovae seem to always explode at the same brightness, this supernova tells us that there are many different paths to a white dwarf star exploding,” he adds.
Reference: “A radio-detected Type Ia supernova with helium-rich circumstellar material” by Eric K. Kuhl, Joel Johansson, Jesper Sollerman, Javier Moldon, Takashi J. Moriah, Seppo Mattila, Steve Schulze, Laura Homyuk, Miguel Perez-Torres, Chelsea Harris, Peter Lundqvist, Matthew Graham, Sheng Yang, Daniel A. Perley, Nora Lynn Strotjohann, Christopher Fremling, Avishai Gal-Yam, Jeremy Lezmi, Kate Maguire , Connor Omand, Matthew Smith, Igor Andreoni, Eric S. Bellm, Joshua S. Blum, Kishalai De, Stephen L. Groom, Mansi M. Castleval, Frank J. Massey, Michael S. Medford, Sungmin Park, Josiah Purdum, Thomas M. Reynolds, Reid Riddle, Estelle Robert, Stuart D. Ryder, Yashvi Sharma, and Daniel Stern, 17 May 2023, Nature.
DOI: 10.1038/s41586-023-05916-w
The article “Radio-detected type Ia supernova with helium-rich circumstellar material” is published in Nature and is led by Erik Kuhl of the Department of Astronomy at Stockholm University and describes the first radio detection of a Type Ia supernova. Co-authors from Stockholm University are Joel Johansson, Jesper Sollerman, Steve Schulze, Peter Lundqvist, Sheng Yang and Conor Omand. This work involves researchers from institutes around the world, including Caltech, the Weizmann Institute, IAA-CSIC, NAOJ, Macquarie University and Trinity College Dublin.
Funding: Swedish Research Council, Wenner-Gren Foundation
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