A surviving companion to a supernova

Seventeen years ago, astronomers witnessed supernova 2001ig go off 40 million light-years away in the galaxy NGC 7424, in the southern constellation Grus, the Crane. Shortly after SN 2001ig exploded, scientists photographed the supernova with the European Southern Observatory’s Very Large Telescope (VLT) in 2002. Two years later, they followed up with the Gemini South Observatory, which tantalisingly hinted at the presence of a surviving binary companion.

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An international team of astronomers led by the AAO’s Stuart Ryder used the Hubble Space Telescope to get the first image of a surviving companion to a supernova. This is the most compelling evidence that some supernova explosions originate in binary star systems. The supernova SN 2001ig was discovered by Australian amateur astronomer Bob Evans.

On 10th December 2001 Australian amateur astronomer Robert Evans discovered an exploding star, a supernova, in the outer edge of the spiral galaxy NGC 7424. This galaxy is located in the southern constellation Grus (the Crane), at about 40 million light-years from us.

From the beginning it was evident that this supernova, named SN 2001ig, was unusual. It was classified as a Type IIb stripped-envelope supernova, meaning that most, but not all, of its outer layer of hydrogen is gone prior to the explosion.

Australian Astronomical Observatory (AAO) astronomer Dr Stuart Ryder has been studying the evolution of SN 2001ig for years. He and an international team of astronomers have now confirmed that the reason for the unusual properties of SN 2001ig is the existence of a companion star to the supernova progenitor.

In a science paper published on 28th March 2018 in the Astrophysical Journal, Ryder and collaborators report the discovery of a surviving companion to SN 2001ig using the Hubble Space Telescope.

This is the first time a surviving companion to a “core-collapse” supernova (when a massive star runs out of fuel in its core and collapses under gravity) has been found, and the most compelling evidence that at least some stripped-envelope supernova events originate in a binary star system.

“We know that the majority of massive stars are in binary pairs,” said Dr Ryder, lead author of the study. “Many of these binary pairs will interact and transfer gas from one star to the other when their orbits bring them close together.”

The first indication that SN 2001ig might have a companion star came from observations conducted by Ryder and his collaborators at the CSIRO’s Australia Telescope Compact Array (ATCA) radio telescope near Narrabri, NSW in 2002.

”We noticed regularly spaced “bumps” in the strength of radio emission from the supernova, leading us to wonder if in fact a companion star was stripping off more gas from the star which ultimately exploded every time their orbits brought them close together”, Dr Ryder says. “But we knew we would have to wait a decade or more for the smoke and debris from the supernova explosion to clear before we could be confident that what was left would be the surviving companion.”

Ryder and his team were finally able to focus the Hubble Space Telescope on the precise location of SN 2001ig 15 years after the explosion. Thanks to Hubble’s ultraviolet capability (something the upcoming James Webb Space Telescope will lack), they were able to find and photograph the surviving companion.

“It was tremendously exciting to have our theory confirmed after all these years, in an object which was first discovered right here in Australia. Bob Evans is such a scrupulous observer who has discovered more than 40 supernovae since 1981, and his discovery of SN 2001ig has turned out to yield a whole new insight into how stars die”, added Dr Ryder.

The AAO is a division of the Department of Industry, Innovation and Science.

Science Contacts:

- Dr Stuart Ryder

Head of International Telescopes Support

Australian Astronomical Observatory

M: +61 419 970 834 E: stuart.ryder@aao.gov.au

Media contact:

- Dr Ángel López-Sánchez

Research Astronomer and Science Communication Officer

Australian Astronomical Observatory and Macquarie University

M: +61 406 265 917 E: angel.lopez-sanchez@aao.gov.au

 

Images:

supernova 2001ig go off 40 million light-years away in the galaxy NGC 742

Caption: Seventeen years ago, astronomers witnessed supernova 2001ig go off 40 million light-years away in the galaxy NGC 7424, in the southern constellation Grus, the Crane. Shortly after SN 2001ig exploded, scientists photographed the supernova with the European Southern Observatory’s Very Large Telescope (VLT) in 2002. Two years later, they followed up with the Gemini South Observatory, which tantalisingly hinted at the presence of a surviving binary companion. As the supernova’s glow faded, scientists focused Hubble on that location in 2016. They pinpointed and photographed the surviving companion, which was possible only due to Hubble’s exquisite resolution and ultraviolet sensitivity. Hubble observations of SN 2001ig provide the best evidence yet that some supernova explosions originate in binary star systems.

Credit: NASA, ESA, S. Ryder (Australian Astronomical Observatory), and O. Fox (STScI).

This image is available at: https://www.aao.gov.au/files/press/2018-04-21-sn2001ig-hst.jpg

This graphic illustrates the scenario for the processes that create a Type IIb stripped-envelope supernova, in which most, but not all, of the hydrogen envelope is lost prior to the primary star’s explosion.

Caption: This graphic illustrates the scenario for the processes that create a Type IIb stripped-envelope supernova, in which most, but not all, of the hydrogen envelope is lost prior to the primary star’s explosion. The four panels show the interaction between the SN 2001ig progenitor star, which ultimately exploded, and its surviving companion. 1) Two stars orbit each other and draw closer and closer together. 2) The more massive star evolves faster, swelling up to become a red giant. In this late phase of life, it spills most of its hydrogen envelope into the gravitational field of its companion. As the companion siphons off almost all of the doomed star’s hydrogen, it creates an instability in the primary star. 3) The primary star explodes in a supernova. 4) As the supernova’s glow fades, the surviving companion becomes visible to the Hubble Space Telescope. The faint remnant of the supernova, at lower left, continues to evolve but in this case is too faint to be detected by Hubble.

Credit: NASA, ESA, and A. Field (STScI).

This image is available at: https://www.aao.gov.au/files/public/images/2018-04-21-sn-type-iib-scenario-ilustration.jpg

Dr Stuart Ryder (left) and Bob Evans (right) attending a supernova conference in Valencia, Spain in 2003.

Caption: Dr Stuart Ryder (left) and Bob Evans (right) attending a supernova conference in Valencia, Spain in 2003.

Credit: S. Ryder (Australian Astronomical Observatory)

This image is available at: https://www.aao.gov.au/files/public/images/2018-04-21-bob-evans-and-stuart-ryder-2002.jpg

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