The modern theory of stellar evolution has been called into question

A recently discovered supernova, whose star ejected as much material as the sun in the year before the explosion, challenges the standard theory of stellar evolution. New observations give astronomers a glimpse of what happens in the final year before a star dies and explodes.

Core collapse supernova and SN 2023ixf SN 2023ixf is a new Type II supernova discovered in May 2023 by amateur astronomer Kōichi Itagaki in Yamagata, Japan, shortly after the explosion of its progenitor, or parent star. Located about 20 million light-years from the Pinwheel Galaxy, SN 2023ixf is close to Earth, and its supernova’s extreme brightness and youth make it a treasure trove of observable data for scientists. study the death of large stars in supernova explosions.

Type II or core collapse supernovae occur when red supergiant stars at least eight times the mass and about 25 times the mass of the Sun collapse under their own weight and explode. Although SN 2023ixf fits the Type II description, follow-up observations at multiple wavelengths were performed by astronomers at the Center for Astrophysics | Harvard & Smithsonian (CfA), and the use of a variety of CfA telescopes, revealed new and unexpected behavior.

Hours after becoming a supernova, a core collapse supernova produces a flash that occurs when the shock wave from the explosion reaches the outer edge of the star.

However, SN 2023ixf produces a slight curve that appears inconsistent with this expected behavior. To better understand the outbreak of the SN 2023ixf shock, a team of scientists led by CfA postdoctoral researcher Daichi Hiramatsu analyzed data from the 1.5m Tillinghast Telescope, 1.2m and SN 2023ixf MMT. located in Arizona. is data from the Global Supernova Project, a key project of Las Cumbres Observatory, NASA’s Neil Gehrels Swift Observatory and many others. This multi-wavelength study, published this week in the Astrophysical Journal, reveals that, in stark contrast to expectations and theories of stellar evolution, the explosion of the SN 2023ixf shock was delayed several days.

“The late onset of the shock is direct evidence for the presence of dense matter due to recent mass loss,” Hiramatsu said, adding that such extreme mass loss is atypical for a Type II supernova. “Our new observations show a large and unexpected loss of mass, nearly the mass of the Sun, in the final year before the explosion.”

SN 2023ixf challenges astronomers’ understanding of the evolution of massive stars and the supernovae they become. Although scientists know that core collapse supernovae are the primary starting point for the formation and cosmic evolution of atoms, neutron stars, and black holes, very little is known about the years before. stellar explosion. New observations highlight potential instability in the final years of a star’s life, leading to extreme mass loss. This may be related to the final stages of nuclear burning of massive elements, such as silicon, in the star’s core.

Along with the multiwavelength observations made by Hiramatsu, Edo Berger, a professor of astronomy at Harvard and CfA and Hiramatsu’s advisor, made millimeter-wave observations of the supernova using submillimeter band (SMA) of CfA at the summit of Maunakea, Hawaii. . These data, published in the Astrophysical Journal, directly tracked collisions between supernova debris and dense matter lost before the explosion. “SN 2023ixf exploded at the right time,” Berger said. “A few days earlier, we launched an ambitious new three-year program to study supernova explosions using the SMA, and this exciting nearby supernova was our first target .”

“The only way to understand how massive stars behave in their final years up to the moment of explosion is to explore supernovae when they are very young and preferably nearby,” Berger said. , then study them across multiple wavelengths.” “Using both optical and millimeter telescopes we effectively turned SN 2023ixf into a time machine to reconstruct what its progenitor star was doing up to the moment of its death.”

The discovery of the supernova and its immediate follow-up has important implications for astronomers around the world, including those who do science in their own backyards. Itagaki discovered the supernova on May 19, 2023 from his private observatory in Okama, Japan. Data compiled from Itagaki and other amateur astronomers determined the time of the explosion to an accuracy of two hours, giving professional astronomers at CfA and other observatories a head start. A favorable start in their investigation. CfA astronomers continue to collaborate with Itagaki on ongoing optical observations. “Collaboration between amateur and professional astronomers has a long history of success in the field of supernovae,” Hiramatsu said. “In the case of SN 2023ixf, I received an urgent email from Kōichi Itagaki as soon as he discovered SN 2023ixf. Without this relationship, and Itagaki’s work and dedication, we would have missed the opportunity to gain an important understanding of the evolution of massive stars and their supernova explosions. .