Astronomers report the discovery of a new supernova in the galaxy UGC 3855. The supernova was discovered using the HMT telescope at the Xingming Observatory in China. The discovery was detailed in a paper published Oct. 7 on the pre-print server arXiv.
Supernovae (SNe) are powerful stellar explosions that could help us better understand the evolution of stars and galaxies. Astronomers divide supernovae into two groups based on their spectra: type I and type II. The spectra of Type I SNEs lack hydrogen, while Type II SNEs exhibit hydrogen spectral lines.
Type Ib supernovae (SNe Ib) are a subclass of SNe that have lost their outer core. They form when a massive star, lacking an outer shell of hydrogen, collapses under its own gravity. Moreover, astronomers also distinguish ultra-short-envelope SNe (USSNe), which exhibit spectral features similar to but weaker than those of SNe Ib/Ic. In these rare cases, the star's shell was severely destroyed before the explosion.
Now a team of astronomers led by Shenyu Yang of Tsinghua University in Beijing, China, reports the discovery of an unusual type Ib USSNe. The supernova was first identified by HMT on December 5, 2021, and designated SN 2021agco.
SN 2021agco was discovered about 130 million light-years away, in the relatively old intermediate spiral galaxy UGC 3855. The supernova is located about 15,600 light-years from the center of the galaxy. SN 2021agco developed very quickly, peaking at -16.06 mag just 2.4 days after the explosion.
The study found that the mass of SN 2021agco was about 0.26 solar masses, and the kinetic energy of the supernova was calculated to be 95.7 quindecillion erg. The researchers calculated that the progenitor star SN 2021agco had an envelope with a radius of about 78.4 solar radii, a mass of 0.1 solar masses, and an ejecta energy of 89.3 quindecillion erg.
According to the authors of the paper, the findings indicate that the progenitor star SN 2021agco lost a lot of mass, and much of its outer layer was stripped off before the explosion.
The observations also revealed some information about the properties of UGC 3855. Astronomers found that the galaxy is approximately 10.6 billion years old and has a mass of about 2.6 billion solar masses. The galaxy has a relatively low star formation rate of 0.2 solar masses per year.