Cosmic Explosions: A Roundup of Recent Supernova Remnant Discoveries

Astronomers have recently published findings on several distinct supernova remnants in different locations within the Milky Way and beyond. Studies using data from the Chandra X-ray Observatory, XMM-Newton, and other telescopes report potential remnants near the Galactic Center, variable X-ray sources in the galaxy M83, and evidence linking two remnants in Gemini to a binary star system origin.

Candidate Supernova Remnant Near Galactic Center

Discovery and Location

Using data from NASA's Chandra X-ray Observatory and ESA's XMM-Newton, a team of astronomers identified a candidate supernova remnant in the Sagittarius C region, approximately 26,000 light-years from Earth, near the center of the Milky Way galaxy. The candidate is located within an H II region—a bubble of ionized gas surrounding a massive young star—which is a known bright radio source also designated Sagittarius C.

If confirmed, this would be one of the closest supernova remnants to the supermassive black hole at the Galactic Center, Sagittarius A*.

Observational Evidence

The evidence comes from a "blob" of X-ray emission detected by Chandra and XMM-Newton. Previous observations with NASA's SOFIA mission had indicated an expanding shell of gas around Sagittarius C, suggesting a stellar explosion. The expanding remnant is estimated to be moving at approximately 3.2 million kilometers per hour (two million miles per hour) and is at least 1,700 years old.

The study was led by Zhenlin Zhu and Mark Morris (UCLA), Gabriele Ponti (INAF, Italy), and Ping Zhou (Nanjing University, China). The paper was published in The Astrophysical Journal.

Alternative Explanations and Data

The team searched for enhanced elemental signatures expected from a supernova but did not find them. Researchers stated this could be because the stellar debris has mixed with surrounding gas. An alternative hypothesis—that the X-ray emission results from gas heated by a cluster of massive stars—was considered unlikely by the team because the X-ray brightness of the blob is over ten times greater than that of known massive star clusters.

Multiwavelength Imaging

Composite imagery of the region includes:

• X-ray data (blue) from Chandra and XMM-Newton
• Radio data (red) from the MeerKAT telescope in South Africa
• Optical data from Pan-STARRS telescopes in Hawaii
• Infrared data (light blue) from the James Webb Space Telescope, showing gas in the H II region

Variable X-ray Sources in M83 Supernova Remnants

Study Overview

Astronomers using the Chandra X-ray Observatory discovered that approximately half of 22 X-ray sources associated with supernova remnants in the galaxy Messier 83 (M83) exhibited significant changes in brightness over a 14-year period (2000–2014). This finding was reported as unexpected by the researchers because older supernova remnants were thought to fade gradually.

M83 is located approximately 15 million light-years from Earth and is classified as a star-forming galaxy.

Observations

Chandra data covered single observations in 2000 and 2001, ten observations from 2010–2011, and one observation in 2014.

Proposed Explanations

Researchers proposed several explanations for the variability:

• Stellar Survivors (High-Mass X-ray Binaries): The variability may arise from systems where a massive star survived its companion's supernova and now orbits a black hole or neutron star. Material pulled from the surviving star onto the compact object produces variable X-rays. Such high-mass X-ray binaries (HMXBs) are known to exhibit high variability.
• Fallback Recycling: Black holes or neutron stars might recapture material ejected by the original supernova, producing variable X-rays.
• Single Remnant Case: One specific remnant, SN 1957D (observed approximately 70 years ago), has been explained as X-ray flares resulting from the blast wave ramming into surrounding material.

Related Findings

A follow-up study of the galaxy M51, using Chandra and ground-based optical data, found a similar population of variable X-ray sources associated with supernova remnants. Researchers stated this suggests such systems may be common in galaxies with vigorous star formation.

The results were presented at the American Astronomical Society meeting in Pasadena, California, and published in The Astrophysical Journal. The lead author was Andrea Prestwich (Catholic University of America).

Potential Binary Supernova System in Gemini

Study Findings

A study of two supernova remnants, G189.6+3.3 and IC 443 (also known as the Jellyfish Nebula), suggests they originated from a binary star system where both stars exploded as supernovae. This is reported as the first known example of a binary system where both stars produced separate, detectable supernova remnants.

The findings were presented at the 248th meeting of the American Astronomical Society and have been accepted for publication in Nature Communications.

Evidence and Measurements

Using 16 years of Fermi Gamma-ray Space Telescope data, researchers detected gamma rays from G189.6+3.3, which had been previously hidden by the brighter Jellyfish Nebula.

The two remnants are located approximately 6,000 light-years away in the constellation Gemini, with explosion centers separated by roughly 40 light-years. The Jellyfish Nebula is estimated to be 8,000–9,000 years old, while G189.6+3.3 is estimated to be 20,000–110,000 years old, indicating the second explosion occurred up to 100,000 years after the first.

Physical Association

A bright gas filament between the remnants shows that both are interacting with the same molecular cloud system. Computer simulations of massive binary systems indicate that such paired explosions with similar separations and time delays are plausible. Researchers stated that the probability of a random alignment producing these observations is less than 1%, supporting a physical association.

Researchers noted the system offers a laboratory to study massive binary evolution, particle acceleration, and coupled supernova remnant behavior.