M83 - A spiral galaxy with an unusual population of supernova remnants located about 15 million light-years from Earth.

This graphic shows two of the X-ray sources in a nearby galaxy that are changing their brightness in surprising ways as described in our latest press release. By analyzing data from NASA’s Chandra X-ray Observatory that span over 14 years, researchers found over 20 previously identified supernova remnants — remains from stars that exploded — that vary unexpectedly in X-ray brightness in Messier 83 (M83). These represent roughly half of the X-ray sources associated with supernova remnants in their sample in M83.

The panel on the left contains a composite image of M83 with X-rays from Chandra (red, green, and blue) and optical light data from NASA’s Hubble Space Telescope (red, green, and blue). The two varying Chandra sources are circled in the composite image and close-up timelapse images of these sources are shown in the panels on the right.

This collection of varying sources is surprising because astronomers expect that about a hundred years after the explosion that created them, supernova remnants do not change their brightness dramatically. Rather, they typically fade in X-rays slowly over time. It would be unusual for M83 to have so many explode less than a century ago.

The most likely explanation given by the research team is that they uncovered a population of stellar survivors — stars that lived through their partner's destruction in a supernova explosion. In this scenario, each variable X-ray source began 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 ultra-dense neutron star. Its companion survived.

Chandra detects X-rays produced by infalling material that becomes superheated by the intense gravitational pull of the compact object. Such systems — known as high-mass X-ray binaries (HMXBs) — are among the most variable X-ray sources in the universe and may be the cause of the variations seen in M83’s supernova remnants. At the distance of M83, the supernova remnants appear as point sources even though they are much larger than the HMXBs they contain, implying that the two sources of X-rays cannot be separated in images.

Astronomers have known about HMXBs for decades, but the difference with this group in M83 is their connection to supernova remnants. Previously only a handful of supernova remnants associated with HMXBs were known across observations of all galaxies and so it is unprecedented to find more than twenty strong candidates in just one galaxy.

There is another possible explanation for the variability seen in the Chandra sources in M83. Rather than feeding off a companion star, the black hole or neutron star may be recapturing some of the material blasted outward in the original explosion. In a possible example of cosmic recycling, debris from the explosion falls back onto the very object the supernova created. The researchers suggest that both explanations could be happening in M83 with different sources in our sample having different origins.

These results were presented at the 248th meeting of the American Astronomical Society meeting in Pasadena, CA. In addition, a paper describing these results, led by Andrea Prestwich (Catholic University, Washington, DC), has been published in The Astrophysical Journal.

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 features a composite image of the nearby galaxy Messier 83, and short timelapse videos of two curious supernova remnants hidden inside.

In the composite image, Messier 83, or M83, is shown to have a spiral structure, viewed straight on. At the center is a brilliant white and yellow pool of light. From that light, spiral arms of hot pink cloud corkscrew out in wide, sweeping arches. The galaxy is covered in a faint grey haze, and flecked with red, green, blue, white, and yellow dots.

In an annotated version of the composite image, two tiny dots to our lower right of center are highlighted by white circles. These are two of the supernova remnants being considered by researchers. Each is examined further in a separate timelapse video.

Over a 14-year period from 2000 to 2014, astronomers pointed NASA’s X-ray observatory at the M83 galaxy. They discovered that about half of the X-ray sources believed to be supernova remnants, the aftermath of stellar explosions, were exhibiting dramatic changes in brightness. This result was entirely unexpected.

Those changes in brightness are highlighted in the timelapse videos. In each video, a series of static images flashes by, focused on one of the two X-ray sources once believed to be supernova remnants. In the videos, the X-ray sources appear as bright blue blobs with glowing cores. But in each image, taken months or years apart, the shapes change, as does the intensity of the blue color, and the brightness of the core. By presenting the substantively different images of the same objects one after another in quick succession, short timelapse videos are created.

The most likely explanation for the changes in brightness is that the team has uncovered a population of stellar survivors, stars that lived through an orbiting partner’s destruction in a supernova explosion. Material is being pulled from the surviving star onto the black hole or neutron star that formed in the supernova, a process known to cause rapid changes in X-ray brightness.