The team behind the eROSITA X-ray instrument aboard the Russian-German Spectrum-Roentgen-Gamma (Spektr-RG) telescope has released its first all-sky survey. This amazing dataset looks at the X-ray sky in higher resolution and with greater sensitivity than has ever been observed, going four times deeper than the ROSAT mission’s all-sky map. This is the first data release from this mission and represents only the beginning of what it will produce. During the next 3.5 years, the spacecraft is scheduled to complete seven survey mappings of the sky that, when combined, will give us five times the sensitivity of this first survey.
The X-ray sky looks very different from what we’re used to with our optical telescopes and eyes. By combining data from more than 400 million photons with X-ray energies between 0.2 and 8 keV, this team has built amazing color images of our high-energy sky that allows us to clearly see these differences. The center of our galaxy appears not as a blob of stars but instead as the center of an hourglass. The two bulbs of the hourglass are Fermi bubbles – bubbles of material that were pushed out and shocked by the energetic feeding of our galaxy’s supermassive black hole at some point in the past. Scattered through the sky are notes of bright light with supernovae remnants and the nearest star-forming regions and galaxy clusters.
Publications of surveys like this enable future research that can statistically analyze how common different kinds of objects may be and understand the systematics of our universe. In general, surveys don’t feature a lot of results. I can tell you the survey is estimated to contain 1.1 million sources that are mostly active galaxies, as well as some stars with strong, magnetically active hot coronas. While of enormous scientific interest, galaxy clusters are just 2% of the sources, and the fraction of sources that are associated with X-ray binaries, supernovae remnants, and star-forming regions is even smaller.
To highlight the quality of their instrument, the team showcased several key features in their data. One of the most stunning is their imagery of the triple nebula Vela, Vela Junior, and Puppis. These three supernovae remnants vary in age and distance, with both Vela and Puppis A containing pulsars. Taken together, they give us a singular perspective on this kind of object.
While less spectacular, my favorite feature in their data is the light echo of a transient X-ray source. At some point in the past, the X-ray binary MAXI J1348-630 went into an outburst and erupted with X-ray light. While some of that light traveled straight toward us, most of it went off in every other possible direction. Some of that other light, however, has scattered off surrounding material and made its way toward us thanks to that bounce. We see that scattered light as a spectacular little ring around the binary.
While the Chandra X-ray Observatory has produced a lot of stunning X-ray images over the years, this is the first time we’ve had an X-ray survey capable of this kind of stunning data collection.