Unprecedented Mass Loss in Supernova Undermines Established Theories of Stellar Evolution

In the year leading up to its transformation into a supernova, the red supergiant star designated as SN 2023ixf lost a surprising amount of mass, approximately equal to the Sun’s own mass. This conceptual representation shows what such an extraordinary mass shedding event may have appeared like before the star’s detonation. Credit: Melissa Weiss/CfA

New findings concerning an extraordinary loss of mass before a recently observed supernova suggest that there might be more intricate processes occurring in a star’s terminal year than previously understood.

A recent discovery of a proximate supernova, in which the star ejected nearly a solar mass of material in the year before it exploded, calls into question existing paradigms of stellar evolution. These latest observations offer astronomers a deeper understanding of events transpiring in the final year before a star’s ultimate demise and explosion.

Core-Collapse Phenomena and SN 2023ixf

SN 2023ixf is a Type II supernova identified in May 2023 by amateur astronomer Kōichi Itagaki of Yamagata, Japan, soon after its precursor star underwent an explosion. Situated approximately 20 million light-years away in the Pinwheel Galaxy, the closeness of SN 2023ixf to Earth, its exceptional luminosity, and its youthful state make it an invaluable source of empirical data for researchers exploring the death of massive stars through supernova events.

Type II supernovae, also known as core-collapse supernovae, are the end result when red supergiant stars, with masses ranging from at least eight to around 25 solar masses, implode due to gravitational forces and subsequently explode. Although SN 2023ixf conforms to the Type II categorization, subsequent multi-wavelength observations spearheaded by scientists at the Center for Astrophysics | Harvard & Smithsonian (CfA) have uncovered unexpected stellar behavior.

Insights from Multi-Wavelength Observations

Within a few hours of becoming a supernova, core-collapse supernovae typically emit a burst of light produced when the explosion’s shock wave interacts with the star’s outer layers. However, SN 2023ixf displayed a light curve inconsistent with this anticipated pattern. To better comprehend the unique aspects of SN 2023ixf’s shock breakout, a research team led by CfA postdoctoral fellow Daichi Hiramatsu scrutinized data from several telescopes, including the 1.5m Tillinghast Telescope, 1.2m telescope, and MMT at the Fred Lawrence Whipple Observatory in Arizona, as well as data from numerous other projects. Published recently in The Astrophysical Journal Letters, this multi-wavelength study revealed an unanticipated delay in SN 2023ixf’s shock breakout, contrary to established theories of stellar behavior.

Implications for Stellar Evolution Theories

“The delay in the shock breakout serves as direct proof of the presence of densely packed material resulting from a recent, anomalous loss of mass,” Hiramatsu commented. This newfound evidence exposes an unusual and significant mass loss—approximately equal to a solar mass—in the final year before the star exploded.

Expanded Observational Approaches

Concurrently with multi-wavelength studies led by Hiramatsu, Edo Berger, a professor of astronomy at Harvard and CfA, conducted additional observations utilizing CfA’s Submillimeter Array (SMA) atop Maunakea, Hawai’i. “The timing of SN 2023ixf’s explosion could not have been more opportune,” Berger noted. “We had just initiated a new, ambitious three-year program focused on supernova research using the SMA, and this nearby and intriguing supernova became our inaugural subject.”

The Role of Amateur Astronomers

The initial discovery and the ensuing immediate analysis hold significant implications for astronomers worldwide, amateur and professional alike. Kōichi Itagaki discovered the supernova on May 19, 2023, from his personal observatory in Okayama, Japan. Joint data gathered by Itagaki and other amateur astronomers allowed for pinpointing the time of the explosion with remarkable precision, thereby enabling a more in-depth scientific inquiry. “The symbiotic relationship between amateur and professional astronomers has long been fruitful in the field of supernova research,” Hiramatsu stated. “In the instance of SN 2023ixf, the contributions and dedication of Kōichi Itagaki were instrumental in advancing our understanding of massive star evolution and supernova mechanisms.”

References:

The original study titled “From Discovery to the First Month of the Type II Supernova 2023ixf: High and Variable Mass Loss in the Final Year before Explosion” was authored by a multi-institutional team and published on September 19, 2023, in The Astrophysical Journal Letters. DOI: 10.3847/2041-8213/acf299

Another paper, titled “Millimeter Observations of the Type II SN 2023ixf: Constraints on the Proximate Circumstellar Medium,” co-authored by Edo Berger and others, was also published in The Astrophysical Journal Letters on July 10, 2023. DOI: 10.3847/2041-8213/ace0c4

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More about Stellar Evolution

• The Astrophysical Journal Letters: From Discovery to the First Month of the Type II Supernova 2023ixf
• The Astrophysical Journal Letters: Millimeter Observations of the Type II SN 2023ixf
• Center for Astrophysics | Harvard & Smithsonian
• Global Supernova Project
• NASA’s Neil Gehrels Swift Observatory
• Fred Lawrence Whipple Observatory
• Submillimeter Array (SMA)
• Introduction to Stellar Evolution