Astronomers See a Dying Star End Explosively

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Artist’s impression of the red supergiant star, in its final year. It emits a turbulent cloud of gas. This suggests that at least some stars go through significant internal changes before becoming supernovae.

Credit: W. M. Keck Observatory/Adam Makarenko

Two Hawai’i Telescopes Take a Huge Star Moments before Going Supernova

Haleakala and Maunakea, Hawai`i For the very first time, astronomers have imaged in real time the dramatic end to a red supergiant’s life, watching the massive star’s rapid self-destruction and final death throes before it collapsed into a Type II supernova.

Using two Hawai`i telescopes – the University of Hawai`i Institute for Astronomy Pan-STARRS on Haleakala, Maui and W. M. Keck Observatory on Maunakea, Hawai`i Island – a team of researchers conducting the Young Supernova Experiment (YSE) transient survey observed the red supergiant during its last 130 days leading up to its deadly detonation.

” This is a major breakthrough in our understanding about what massive stars do moments prior to their death,” Wynn Jacobson Galan, a NSF Graduate Research Fellow at UC Berkeley, and the lead author of this study. “Direct detection in a red supergiant supernova of pre-supernova activity has never before been possible in an ordinary Type II supernova. We witnessed the first supergiant star explosion

The discovery is published in today’s issue of The Astrophysical Journal.

Pan-STARRS first detected the doomed massive star in Summer of 2020 via the huge amount of light radiating from the red supergiant. A few months later, in Fall of 2020, a supernova lit the sky.

The team quickly captured the powerful flash and obtained the very first spectrum of the energetic explosion, named supernova 2020tlf, or SN 2020tlf, using Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS). Data showed that the star was surrounded by dense circumstellar material at the time of the explosion. This is likely the exact same gas that Pan-STARRS had seen earlier in the summer.

Artist’s rendering of a red supergiant turning into a Type II Supernova. It emits a powerful eruption of radiation and gases on its dying breath, before collapsing. Credit: W. M. Keck Observatory/Adam Makarenko

“Keck was instrumental in providing direct evidence of a massive star transitioning into a supernova explosion,” says senior author Raffaella Margutti, an associate professor of astronomy at UC Berkeley. It’s like watching a ticking bomb. It’s like watching a ticking time bomb. We haven’t seen such intense activity in a dying supergiant star.

The team continued to monitor SN 2020tlf after the explosion; based on data obtained from Keck Observatory’s DEep Imaging and Multi-Object Spectrograph (DEIMOS) and Near Infrared Echellette Spectrograph (NIRES), they determined SN 2020tlf’s progenitor red supergiant star, located in the NGC 5731 galaxy about 120 million light-years away as seen from Earth, was 10 times more massive than the Sun.

This discovery challenges previous theories about how supergiant stars develop right before they explode. Prior to this, all red supergiants observed before exploding were relatively quiescent: they showed no evidence of violent eruptions or luminous emission, as was observed prior to SN 2020tlf. This new detection of bright radiation from a red giant in the last year before it explodes suggests that at most some stars have undergone significant structural changes that result in the tumultuous emission of gas just moments before they collapsing.

Margutti and Jacobson–Galan carried out most of the research during their time at Northwestern University. Margutti was an Associate Professor in Physics and Astronomy and a member of CIERA (Center for Interdisciplinary Exploration and Research in Astrophysics). Jacobson–Galan was a graduate student.

The team’s discovery opens up a pathway for transient surveys such as YSE to search for luminous radiation from red supergiants and collect more evidence that such behavior might indicate the impending, supernova death of a large star.

” I am most excited about all of the new “unknowns” that have been unlocked through this discovery,” states Jacobson-Galan. “Detecting more events like SN 2020tlf will dramatically impact how we define the final months of stellar evolution, uniting observers and theorists in the quest to solve the mystery on how massive stars spend the final moments of their lives.”


The Low Resolution Imaging Spectrometer (LRIS) is a very versatile and ultra-sensitive visible-wavelength imager and spectrograph built at the California Institute of Technology by a team led by Prof. Bev Oke and Prof. Judy Cohen and commissioned in 1993. It has been upgraded twice to improve its capabilities. A second, blue arm was added that is optimized for shorter wavelengths of light. Detectors that are more sensitive at longer wavelengths (red) have also been installed. Each arm is optimized to cover the specific wavelengths. The instrument’s wide wavelength coverage combined with its high sensitivity allows for the study of all things, from comets (which exhibit interesting features in ultraviolet), to the blue light of star formation, and the red light of distant objects. LRIS also records the spectra of up to 50 objects simultaneously, especially useful for studies of clusters of galaxies in the most distant reaches, and earliest times, of the universe. LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in 2011 for research determining that the universe was speeding up in its expansion.


The DEep Imaging and Multi-Object Spectrograph (DEIMOS) boasts the largest field of view (16.7arcmin by 5 arcmin) of any of the Keck Observatory instruments, and the largest number of pixels (64 Mpix). It is used primarily in its multi-object mode, obtaining simultaneous spectra of up to 130 galaxies or stars. With DEIMOS, astronomers can study distant galaxies and probe the most remote corners of the universe using high sensitivity.


The Near Infrared Echellette Spectrograph is a prism-cross-dispersed near infrared spectrograph that was built at the California Institute of Technology. It was developed by a team of Chief Instrument Scientist Keith Matthews, and Prof. Tom Soifer. Commissioned in 2018, NIRES covers a large wavelength range at moderate spectral resolution for use on the Keck II telescope and observes extremely faint red objects found with the Spitzer and WISE infrared space telescopes, as well as brown dwarfs, high-redshift galaxies, and quasars. The Mt. Cuba Astronomical Foundation.


The W. M. Keck Observatory telescopes have the highest scientific productivity on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawai`i feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The W. M. Keck Foundation provided financial support that enabled the Observatory to be built. We acknowledge and respect the significant cultural significance and reverence Maunakea’s summit has had in the Native Hawaiian community. It is a great privilege to be able to observe this mountain.

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