SRG/eROSITA discovers and studies supermassive black holes in the early Universe

SRG/eROSITA discovers and studies supermassive black holes in the early Universe 

In the center of our Galaxy lurks a black hole with a mass of 4 million solar masses. Such black holes are present in almost all galaxies. Typically, they are even larger, in some cases reaching several billion solar masses. Such supermassive black holes (SMBHs) were born many billion years ago, when the first stars and galaxies just started to appear in the Universe, and then have grown by accreting surrounding matter. During this process huge amounts of energy were released, which allows us to observe young, growing massive black holes via their electromagnetic radiation emitted many billion years ago. Such objects are called quasars (quasi-stellar objects).

How SMBHs form and grow is one of the main scientific problems addressed by the Russian orbital observatory SRG, which on July 13 marks its first year in orbit since the launch from the Baikonur Cosmodrome. In early June 2020, eROSITA, one of the two telescopes aboard the observatory, had finished its first (out of the planned eight) survey of the whole sky in X-rays. More than a million X-ray sources have been found during this survey. In addition, to study more distant and fainter objects, eROSITA has conducted a deeper scan of the Lockman Hole, a small region of the sky where absorption of X-rays by the interstellar gas and dust in our Galaxy is minimal and does not hinder observations of extragalactic objects.

A team of scientists from the Space Research Institute (IKI) of the Russian Academy of Sciences led by Marat Gilfanov and Sergey Sazonov are working on the catalog of eROSITA sources and use it to search for the most distant and fastest growing SMBHs in the early Universe. A neural network “SRGz”, developed at IKI by Alexander Mescheryakov, has selected several tens of candidate distant quasars from more than half a million X-ray sources found by eROSITA on the hemisphere allotted to Russian scientists. The most interesting of them were then observed at optical telescopes as part of the ground support program of the SRG sky survey.

Already the first observations have led to the discovery of previously unknown quasars. Among them are

  • a quasar at z=4.116, discovered at the AZT-33IK 1.6-meter telescope of the Sayan Observatory of the Institute of Solar-Terrestrial Physics in Buryatia;
  • a quasar at z=4.237, discovered at the Russian-Turkish 1.5-meter Telescope (RTT-150) in Turkey;
  • a quasar at z=4.576, discovered at the BTA 6-meter telescope of the Special Astrophysical Observatory in Karachay-Cherkessia.

These observations were carried out under the leadership of Rodion Burenin and George Khorunzhev from IKI and Ilfan Bikmaev from the Kazan Federal University (KFU).

In addition, observations performed at the 2.5-meter telescope of the Caucasus Mountain Observatory of the Sternberg State Astronomical Institute of the Moscow State University have confirmed that several other candidates are also quasars.

The letter “z” used above denotes an object’s redshift, which defines its distance. Quasar redshifts are measured through the positions of bright emission lines in their spectra. The most prominent is the Lyman-alpha line known from high-school physics. It results when the electron in a hydrogen atom makes a transition from the second to the first level. In usual conditions, this line appears in the ultraviolet part of the spectrum, but it falls into the visible band in the spectra of distant quasars owing to the large redshift caused by the expansion of the Universe.

Optical spectra of three previously unknown quasars at redshift z>4 discovered by SRG/eROSITA. These objects were found by the SRGz neural network among nearly half a million X-ray sources detected by SRG/eROSITA, and their nature was confirmed by means of optical spectroscopy at the BTA, RTT-150 and AZT-33IK telescopes. 


Particularly interesting are quasars at redshifts z>6, belonging to an epoch when the Universe was younger than one billion years. It remains unclear how some black holes managed to grow to several billion solar masses in a such a short time by cosmological standards. Another key question in modern astrophysics is the relationship between star formation in the first galaxies and growth of black holes in their nuclei. Finally, it is not fully clear what role quasars played in the reionization of the Universe, which occurred between 200 million and 1 billion years after the Big Bang. More than 200 quasars at z>6 have already been unveiled by optical and infrared observations, and just some 20 of them have been detected in X-rays.

In a paper accepted for publication in the Monthly Notices of the Royal Astronomical Society, Pavel Medvedev and his colleagues from IKI and KFU report the discovery by SRG/eROSITA of X-rays from quasar CFHQS J1429+5447 at z=6.2 (corresponding to an age of the Universe of 900 million years). This quasar was previously known from observations in the visible and radiobands, but its X-ray radiation has been found for the first time. According to eROSITA, the quasar’s X-ray luminosity is about 3×1046 erg per second, which is several times higher than the previous record for z>6 quasars. Since the quasar emits radiation across the electromagnetic spectrum from radio to UV and X-rays, its total luminosity is actually yet higher by an order of magnitude – about 3×1047 erg/s. For comparison, the total luminosity of all two hundred billion stars in our Galaxy is a thousand times lower! This implies that the black hole in this quasar weighs more than 2 billion solar masses and it must have been “swallowing” approximately one Earth mass each second for several tens of millions of years.

Quasar CFHQS J1429+5447 fell into the field of view of eROSITA and was detected by it during scans of the sky on December 10-11, 2019, at the very beginning of the SRG all-sky survey. Follow-up observations at RTT-150 revealed that the optical brightness of the quasar remained nearly the same as it was 10 years ago when it was discovered by the Canada-France-Hawaii Telescope.


Quasar CFHQS J1429+5447 is known to be “radio loud”. Its powerful radio emission presumably originates in a pair of jets launched at almost the speed of light from the vicinity of the black hole. Medvedev and his colleagues suggested that the record-breaking X-ray luminosity of this quasar is associated with the Compton scattering of the relic radiation from the Big Bang by the relativistic matter of the jets. This process should be especially important in the early Universe, where the energy density of the relic radiation was some three orders of magnitude higher than that of the cosmic microwave background around the present-day objects. IKI scientists continue to look for such objects in the eROSITA data.

The first SRG/eROSITA X-ray image

On August 26, 2019 the first X-ray image was obtained by one of the seven eROSITA telescope modules  on board the Spektr-RG space observatory. 

The image of the UDS field with an area of the order of one square degree clearly shows dozens of X-ray sources, mainly active galactic nuclei and quasars. The image was obtained with the exposure of about 2000 seconds in the 0.5–2 keV energy range. Data obtained by Russian and German consortiums of the SRG/eROSITA mission.

The first X-ray image obtained by one of the seven eROSITA telescope modules on board the Spektr-RG space observatory in the 0.5-2 keV energy range. Data obtained by Russian and German consortiums of the SRG/eROSITA mission.

SRG/ART-XC continues to see activity from Sgr A*

ATel #13039M. Pavlinsky on behalf of the ART-XC collaboration (Space Research Institute (IKI), Moscow, Russia)

The ART-XC telescope onboard Spektr-RG space observatory continues to monitor the Galactic center region after reports on Sgr A* flaring activity (ATel #13007, #12768).

Recent ART-XC observations of Sgr A* on August 15-16 (2019-08-14T23:40 – 2019-08-15T14:00 and 2019-08-15T23:40 – 2019-08-16T14:00, UTC) with total exposure of 50 ks each, demonstrate source average 5-16 keV flux at the level of 1.6×10-11 erg cm-2 s-1, which corresponds to the luminosity of 1.4×1035 erg s-1 , assuming a distance of 8.5 kpc. This measurement of the source luminosity is comparable to that observed with ART-XC on August 12 (ATel #13023). We also see a small flux variability at the level of 15% on the timescale of a few hours. More detailed information will be provided in the corresponding publication, which is under preparation.

Multi-wavelength observations are encouraged; next time when ART-XC will observe Sgr A* is between 2019-08-22T05:46 and 2019-08-22T15:20 UTC.

The first scientific publication: SRG/ART-XC observes activity from Sgr A*

The SRG/ART-XC collaboration sent its first astronomic “telegram” on observing the supermassive black hole Sagittarius A* in the center of the Milky Way.

ATel #13023; M. Pavlinsky on behalf of ART-XC collaboration (IKI RAS, Moscow)
on 13 Aug 2019; 21:56 UT

Following the recent report on Sgr A* flaring activity (ATel #13007, #12768) ART-XC telescope onboard Spektr-RG observed the Galactic center region for 50 ks during the period between 2019-08-11 22:27:50 UTC and 2019-08-12 13:19:12 UTC

We found Sgr A* in unusually active state: using absorbed power-law spectral model (slope Γ=2, following Zhang+17) we estimated mean flux in 5-16 keV band as (1.6±0.2)x10-11 erg cm-2 s-1, which corresponds to the unabsorbed bolometric luminosity of 2×1035 erg s-1 (0.1-20 keV), assuming a distance of 8.5 kpc.

We also noticed variability on timescale of few kiloseconds.
Because of preliminary calibration status of ART-XC more accurate details will be provided in the following article.

Multi-wavelength observations are encouraged; ART-XC will observe Sgr A* between 14.08.2019 23:40 and 15.08.2019 15:20 UTC

HEASARC Picture of the week

Seven First Lights of ART-XC

One of the most exciting times in the life of any astronomical observatory is achieving “first light“, the first time a telescope produces an image of an astronomical object. For space-based observatories, this can be a time that’s especially nerve-wracking, given the remote nature of the science and the fact that it can be difficult to address problems in deep space. As capabilities grow, and observatories are placed farther from earth, problems encountered are ever harder to resolve. The Spektr-RG observatory (or SRG as it’s more commonly known) is a Russian-German X-ray observatory, launched on July 13, and currently on a journey to its final staging point, a region of precarious orbital stability in the earth-Sun system called “L2”, about a million miles from earth along the earth-Sun line. Once it arrives at L2, SRG will survey the entire sky every six months over the next four years. SRG consists of two observing instruments. The Astronomical Roentgen Telescope X-ray Concentrator (ART-XC) instrument consists of 7 individual telescopes whichwill generate images of the X-ray sky in the energy band from 5 kilo-electronvolts up to 30 kilo-electronvolts, which is about 3 times higher in energy than most other imaging X-ray observatories, like ChandraXMM-Newton and Swift. ART-XC was developed by the Russian Academy of Sciences’ Space Research Institute, in cooperation with the Russian Federal Nuclear Centre; NASA’s Marshall Space Flight Center provided ART-XC’s X-Ray mirrors. The image above is the first light image from the 7 ART-XC telescopes, obtained on July 30, 2019. This image shows the well-known X-ray pulsar Cen X-3, a binary system in which a spinning neutron star (rotating once every 4.8 seconds) is in a 2-day orbit around Krzeminski’s star, a massive star about 20 times the mass of the Sun. ART-XC can also measure the time variation of the observed X-rays, and the plot on the bottom of the image clearly shows the 4.8 second X-ray variation of the pulsar as measured by ART-XC. eROSITA, developed by Germany’s Max Planck Institute, is the second instrument on SRG, and is expected to achieve first light in the coming weeks.

Published: August 12, 2019 


The new image obtained by ART-XC

During the ART-XC calibration observations on August 3, the collaboration received a new scientific image:

 Centaur X-3
The X-Ray pulsar Centaur X-3 (Cen X-3) in the ART-XC telescope central field of view.

As of August 7, 2019, the Spektr-RG spacecraft was continuing its flight to the L2 Sun – Earth system libration point area, the onboard equipment being adjusted. The ART-XC telescope creators expect to receive the images from the second telescope, eROSITA, to collate the fields of view of both telescopes.

eROSITA, the second telescope of the project was created in Germany. The spacecraft has already opened the lid used to cover the mirror systems entrance openings. eROSITA is expected to send its first images in mid-September.

Spektr-RG is a Russian-German joint project to create a space astrophysical observatory aimed to explore the Universe in the X-Ray electromagnetic radiation spectrum around the Sun – Earth system L2 point. The spacecraft was launched on July 13 2019 from the Baikonur Cosmodrome.

INTEGRAL coordinated observations of Cen X-3

31 July 2019 INTEGRAL is currently observing the High Mass X-ray Binary Cen X-3. The source is the target selected for the first light of the ART-XC detector onboard the Spektr-RG mission.

INTEGRAL observations will provide complementary information of the source at hard X-rays and will help to characterise the performance of the ART-XC detector in space. Spektr-RG was launched from the Baikonur Cosmodrome on 13 July 2019. We wish sucessful operations to our Spektr-RG colleagues.

Source: INTEGRAL ESA Mission