The spiral galaxy NGC 3621, as seen by the European Southern
Observatory’s Very Large Telescope, hosted the latest nearby supernova,
SN 2024ggi. Credit: ESO, CC BY 4.0
Less than a year after SN 2023ixf captivated astronomers worldwide, another nearby supernova burst onto the scene. At a distance of just 22 million light-years, SN 2024ggi provides another excellent opportunity to study the behavior of red supergiant stars in their final years.
Less than a year after SN 2023ixf captivated astronomers worldwide, another nearby supernova burst onto the scene. At a distance of just 22 million light-years, SN 2024ggi provides another excellent opportunity to study the behavior of red supergiant stars in their final years.
Live Fast, Die Spectacularly
The discovery of a new nearby supernova marks the beginning of a
cosmic chase. After astronomers pinpoint a rapidly brightening point of
light in a distant galaxy — a new supernova! — they hunt through
archival data to learn more about the star that exploded. Using this
method, researchers have tracked down dozens of supernova progenitor
stars and have learned that core-collapse supernovae usually arise from
red supergiant stars with masses in the range of 8 to 18 solar masses.
Supernova hunters have been busy recently: while the dust was still settling from SN 2023ixf — the nearest bright supernova in nearly a decade — the Asteroid Terrestrial-impact Last Alert System discovered the supernova SN 2024ggi on 11 April 2024 in the galaxy NGC 3621. This marks the first time a supernova has been recorded in this galaxy, which is just barely more distant than SN 2023ixf’s host galaxy. What can archival observations tell us about this supernova’s progenitor star?
Supernova hunters have been busy recently: while the dust was still settling from SN 2023ixf — the nearest bright supernova in nearly a decade — the Asteroid Terrestrial-impact Last Alert System discovered the supernova SN 2024ggi on 11 April 2024 in the galaxy NGC 3621. This marks the first time a supernova has been recorded in this galaxy, which is just barely more distant than SN 2023ixf’s host galaxy. What can archival observations tell us about this supernova’s progenitor star?
Images of SN 2024ggi’s progenitor from Hubble (top row) and Spitzer (bottom row).
Credit: Xiang et al. 2024
Credit: Xiang et al. 2024
Archival Analysis
A team led by Danfeng Xiang and Jun Mo (Tsinghua University) turned to observations from the Hubble and Spitzer space telescopes to track down SN 2024ggi’s progenitor. In Hubble images from 1994 to 2003, the team spotted an extremely red star at the location of SN 2024ggi. The star’s reddish hue is likely due to dust that formed around the star in cast-off stellar material.
In Spitzer images of NGC 3621 from 2004 to 2019, the same star is faintly visible but crowded by other stars. By carefully removing the light from the star’s close neighbors, the team was able to monitor the star’s brightness over many years. They found that its brightness varied at both infrared and optical wavelengths with a period of about 378 days. This type of variability is common in red supergiant stars and is likely due to radial pulsations.
In Spitzer images of NGC 3621 from 2004 to 2019, the same star is faintly visible but crowded by other stars. By carefully removing the light from the star’s close neighbors, the team was able to monitor the star’s brightness over many years. They found that its brightness varied at both infrared and optical wavelengths with a period of about 378 days. This type of variability is common in red supergiant stars and is likely due to radial pulsations.
Observed spectral energy distribution of SN 2024ggi’s progenitor star (black squares). The lines show the best-fit spectral energy distributions for the model with dust (red) and without dust (gray). Adapted from Xiang et al. 2024
Surprisingly Dust Free
Xiang and Mo’s team also plotted the star’s spectral energy distribution, or how its energy output is spread across different wavelengths of light. They used two classes of models to interpret the spectral energy distribution: one model that included a veil of dust around the star and one that was dust free.
These models suggested that the star had a mass around 13 solar masses and its temperature was a cool 3290K. Surprisingly, given the star’s extremely red color, the dusty and dust-free models both fit the data well, suggesting that the dust shell around the star was thin.
The thinness of the dust shell implies a low mass-loss rate for the star in the decades before its explosion, but researchers studying the subsequent supernova found the star’s mass-loss rate just before its demise to be much higher. This might mean that while SN 2024ggi’s progenitor shed mass at a modest rate during most of its life, it shed far more mass in its final years. This finding adds to the growing body of evidence that red supergiants undergo stellar tantrums before their ultimate explosions.
These models suggested that the star had a mass around 13 solar masses and its temperature was a cool 3290K. Surprisingly, given the star’s extremely red color, the dusty and dust-free models both fit the data well, suggesting that the dust shell around the star was thin.
The thinness of the dust shell implies a low mass-loss rate for the star in the decades before its explosion, but researchers studying the subsequent supernova found the star’s mass-loss rate just before its demise to be much higher. This might mean that while SN 2024ggi’s progenitor shed mass at a modest rate during most of its life, it shed far more mass in its final years. This finding adds to the growing body of evidence that red supergiants undergo stellar tantrums before their ultimate explosions.
Citation
“The Red Supergiant Progenitor of Type II Supernova 2024ggi,” Danfeng Xiang et al 2024 ApJL 969 L15. doi:10.3847/2041-8213/ad54b3
By Kerry Hensley
