ROSCOSMOS & DLR - Spectrum Roentgen Gamma (Spektr-RG) patch.
June 19, 2020
A week ago, the ART-XC and eROSITA telescopes, mounted on board the Russian Spectrum-RG orbital observatory, completed scanning of the entire sky in X-rays. Work on building a map and determining the number of sources detected during the scan continues. Russian scientists process data from one side of the sky, and German scientists work with x-ray photons that came from the other half of the sky. The map of the whole sky, built by scientists of two scientific consortia and shown in the illustration, was surprisingly informative.
At the very center of the map is a supermassive black hole with a mass of 4 million solar masses (this is a rather weak x-ray source). At the equator of the image passes the plane of the Milky Way galaxy, which we can observe in full glory in the south of our country on a moonless summer night. On the X-ray map, the Milky Way looks like a dark strip due to the fact that molecular gas and dust in the plane of the Galaxy absorb X-rays. The blue dots located in this region demonstrate the presence of a large number of bright and powerful sources of X-ray radiation in the Milky Way - these are X-ray pulsars accreting black holes in binary stellar systems, the remnants of supernova explosions (the result of recent star death).
This card is multicolor, and various colors immediately allow you to judge the characteristic energy of incoming photons. It shows all X-ray photons recorded by eROSITA detectors in the energy range from 300 electron-volts to 2.3 kiloelectron-volts for half a year of continuous scanning of the sky. Red color corresponds to photons with an energy of 0.3-0.6 keV, green - 0.6-1 keV, blue - 1-2.3 keV. For ease of understanding, we can say that these three energy ranges correspond, for example, to the temperature of a radiating hot substance from 3 million to 6 million degrees (red); from 6 to 10 million degrees (green) and from 10 to 25 million degrees (blue).
Good angular resolution (~ 20 arc seconds) and the highest sensitivity of the eROSITA telescope allowed it to map over a million compact sources and tens of thousands of extended ones. Such a quantity cannot be demonstrated in a single image. Only the brightest of the sources are visible on the map as dots. The very first sky survey by the Russian Astrophysical Observatory “Spectrum-RG” allowed the eROSITA telescope to construct a map containing almost 10 times more sources and four times more sensitive than the former best-in-the-world map of the German satellite ROSAT, obtained in 1990. In just six months of sky scanning, eROSITA was able to double the total number of sources recorded by all satellites in the world in 60 years of X-ray astronomy.
“This map of the whole sky completely changes our view of high-energy processes in the Universe,” says Peter Predel, scientific director of the eROSITA telescope at the Max Planck Institute for Extraterrestrial Physics. “We see such a wealth of detail - the beauty of this image is simply amazing.”
This map allows you to see how hundreds of supernova explosions, and possibly the activity, from time to time, of a supermassive black hole in the center of the Galaxy, lead to gushing emissions of hot gas with temperatures up to 10 million degrees from the plane of our Galaxy (bright zones above and below the plane Galaxies). About two hundred thousand stars quite close to us with crowns much more powerful than those of our Sun also contribute to the emission of zones with a lower temperature.
Three quarters of all objects on this map are distant quasars and nuclei of active galaxies, that is, supermassive black holes emitting due to the fall of matter on them. They are located far beyond the Milky Way at distances of hundreds of millions and billions of light years from us. Among the newly discovered objects on this map, quasars with redshifts of more than 6 have already been found (all lines in their spectra are shifted to the red side more than 7 times due to the expansion of the Universe). We see on the map about 20 thousand clusters of galaxies filled with the mysterious "dark matter". Using optical telescopes to obtain complete information on the redshifts of most quasars and clusters of galaxies discovered by the eROSITA telescope will take years.
Spektr-RG / SRG (Spectrum Roentgen Gamma) satellite
“But now we can begin to use this set of objects located at gigantic distances to determine the time of their appearance in the Universe and to clarify its properties and parameters, that is, for the purposes of cosmology,” says academician of the Spectrum RG observatory academician Rashid Sunyaev.
The telescopes of the Spectrum RG observatory continue to work, it is planned that in a few days it will begin a second survey of the sky. It is expected that it will last until the end of the year. In total, it is planned to get seven more such eROSITA cards - it will take another three and a half years. The total map will be about 5 times more sensitive than the first, and the number of sources on it should increase by more than 10 times.
“Then there will be confidence that our maps and source catalogs will be used by astrophysicists and cosmologists of all countries of the world for at least the next twenty years, until more advanced X-ray telescopes appear, and scientists decide that it is time to create a new, more sensitive map of the X-ray sky” - notes Rashid Sunyaev.
Relate article in Russian:
Рентгеновская карта неба от eROSITA: https://www.roscosmos.ru/28676/
ROSCOSMOS Press Release: https://www.roscosmos.ru/28703/
Related links in Russian:
ART-XC: https://www.roscosmos.ru/28668/
eROSITA: https://www.roscosmos.ru/28676/
«Спектр-РГ» - (Spectrum-RG): https://www.roscosmos.ru/srg/
Related links in English:
Spectrum-RG: http://arc.iki.rssi.ru/eng/srg.htm
Spectrum-Roentgen-Gamma: http://srg.iki.rssi.ru/?lang=en
Images, Text, Credits: ROSCOSMOS/Orbiter.ch Aerospace/Roland Berga.
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