The aftermath of a supernova, a star explosion, is usually a slowly dissipating cloud of hot gas. So when astronomers pointed NASA’s Chandra X-ray observatory at the nearby galaxy Messier 83 (M83), they didn’t expect to find a cluster of supernova remnants, or debris from these explosions, showing dramatic changes in brightness. The new findings were presented at the American Astronomical Society meeting in Pasadena, California, and published in the Astrophysical Journal.
Galaxy M83, located about 15 million light-years from Earth, is forming stars at a high rate. The researchers analyzed 14 years of Chandra data for the galaxy, spanning from 2000 to 2014.
Using this broad data set, researchers discovered striking differences in the X-ray brightness of sources previously identified as supernova remnants. The researchers expected that supernova remnants older than a century or so would gradually fade in X-rays, but not change significantly in brightness.
The team found that nearly half of the 22 X-ray sources associated with supernova remnants in the sample showed changes in X-ray brightness over 14 years of observations, a completely unexpected result.
“We knew that individual X-ray sources can vary greatly,” said Andrea Prestwich of The Catholic University of America, who led the study. “But discovering that many supernova remnants were behaving this way was a real surprise. There is something unusual going on in these objects. Pinpointing the cause remains a challenge, as M83’s distance limits the details we can observe.”
One of the 22 variable supernova remnants has a straightforward explanation: SN 1957D, the supernova debris first observed nearly 70 years ago, collides with material surrounding the site of the explosion, producing the observed X-ray flares. But this cannot explain the rest of the sample. There is no evidence to suggest that all 22 remnants were formed within the past century. There must be something else driving this discrepancy.
The most likely explanation is that the team discovered a group of surviving stars that lived through their partner’s destruction in a supernova explosion. In this scenario, each variable X-ray source started out as a pair of massive stars orbiting each other. The more massive star collapsed and exploded as a supernova, leaving behind a black hole or superdense neutron star. Her companion survived.
“This galaxy likely contains a cluster of supernova remnants where a massive star escapes the supernova and becomes trapped in the orbit of a black hole or neutron star,” said co-author Michael McCullough of the Center for Astrophysics. Harvard and Smithsonian (CfA). “The neutron star or black hole could then begin pulling material from the surface of the massive star.”
This infalling matter is superheated by intense gravity, producing the X-rays discovered by Chandra. These types of systems, known as high-mass X-ray binaries (HMXBs), are among the most variable X-ray sources in the universe. Researchers say it may be the reason for the differences seen in the M83 supernova remnant.
Astronomers have known about HMXBs for decades, but the difference with this group in M83 is its association with supernova remnants. Previously, only a few supernova remnants associated with HMXB have been identified across observations of all galaxies. It is unprecedented to find more than 20 strong candidates in just one galaxy.
The researchers found that the variable supernova remnants are located in regions with higher concentrations of massive stars than in other parts of the galaxy, increasing the chances of a link between the remnants and HMXB.
There’s another possible explanation: Instead of pulling material from the companion star, the black hole or neutron star might reclaim some of the material that was blasted outward by the original explosion.
“This may be an example of cosmic recycling, where debris from the explosion falls back onto the same body that the supernova created,” said co-author Roy Kilgaard of Wesleyan University. “It is very likely that both explanations exist, as the different sources in our sample may have different origins.”
These results are not unique to M83. A follow-up study of the nearby star-forming galaxy M51, conducted by Zoe Hoyland of Vassar and Kilgaard College, revealed a similar cluster of variable X-ray sources associated with supernova remnants, suggesting that such systems may be a feature of galaxies undergoing strong star formation.
Chandra data for galaxy M83 began with single observations in 2000 and 2001, followed by 10 observations from 2010 to 2011 and another observation in 2014.
NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
This release contains a composite image of nearby galaxy Messier 83, and short time-lapse videos of two curious supernova remnants hiding inside.
In the composite image, Messier 83, or M83, appears to have a spiral structure, when viewed directly. In the center is a brilliant array of white and yellow light. From those light spiral arms of hot pink cloud twisted in wide, sweeping arcs. The galaxy is covered in a faint gray haze, speckled with red, green, blue, white and yellow dots.
In an annotated version of the composite image, two small dots at the bottom right of center are highlighted by white circles. These are two supernova remnants that researchers are studying. Each is examined further in a separate video.
Over the course of 14 years from 2000 to 2014, astronomers pointed NASA’s X-ray observatory toward the galaxy M83. They discovered that about half of the X-ray sources believed to be supernova remnants, the effects of stellar explosions, were showing dramatic changes in brightness. This result was completely unexpected.
These changes in brightness are highlighted in time-lapse videos. In each video, a series of still images flash, focusing on one of two X-ray sources previously thought to be supernova remnants. X-ray sources appear in the videos as bright blue dots with glowing cores. But in each image, separated by months or years, the shapes change, as do the intensity of the blue color and the brightness of the nucleus. By showing fundamentally different images of the same objects one after another in quick succession, short time-lapse videos are created.
The most likely explanation for the changes in brightness is that the team discovered a population of survivor stars, stars that lived through the destruction of an orbital partner in a supernova explosion. Material from the surviving star is pulled into the black hole or neutron star that formed in the supernova, a process known to cause rapid changes in X-ray brightness.
Read more from NASA’s Chandra X-ray Observatory
To learn more about NASA’s Chandra mission, visit:
https://science.nasa.gov/chandra
Megan Watsky
Chandra X-ray Centre
Cambridge, Massachusetts.
617-496-7998
[email protected]
Joel Wallace
Marshall Space Flight Center, Huntsville, Alabama
256-544-0034
[email protected]
