Presskit for the eROSITA First All-Sky Survey

June 19, 2020

Additional images from the first all-sky survey by the eROSITA X-ray telescope.
You are free to use the images for your eROSITA reporting, please give the appropriate credit with each image.

The energetic universe as seen with the eROSITA X-ray telescope.

The first eROSITA all-sky survey was conducted over a period of six months by letting the telescope rotate continuously, thus providing a uniform exposure of about 150-200 seconds over most of the sky, with the ecliptic poles being visited more deeply. As eROSITA scans the sky, the energy of the collected photons is measured with an accuracy ranging from 2% - 6%. To generate this image, in which the whole sky is projected onto an ellipse (so-called Aitoff projection) with the centre of the Milky Way in the middle and the body of the Galaxy running horizontally, photons have been colour-coded according to their energy (red for energies 0.3-0.6 keV, green for 0.6-1 keV, blue for 1-2.3 keV). The original image, with a resolution of about 10”, and a corresponding dynamic range of more than one billion, is then smoothed (with a 10’ FWHM Gaussian) in order to generate the above picture.

The red diffuse glow away from the galactic plane is the emission of the hot gas in the vicinity of the solar system (the Local Bubble). Along the plane itself, dust and gas absorb the lowest energy X-ray photons, so that only high-energy emitting sources can be seen, and their colour appears blue in the image. The hotter gas close to the galactic centre, shown in green and yellow, carries imprinted the history of the most energetic processes in the life of the Milky Way, such as supernova explosions, driving fountains of gas out of the plane, and, possibly, past outburst from the now dormant supermassive black hole in the centre of the galaxy. Piercing through this turbulent, hot diffuse medium, are hundreds of thousands of X-ray sources, which appear mostly white in the image, and uniformly distributed over the sky. Among them, distant active galactic nuclei (including a few emitting at a time when the Universe was less than one tenth of its current age) are visible as point sources, while clusters of galaxies reveal themselves as extended X-ray nebulosities. In total, about one million X-ray sources have been detected in the eROSITA all-sky image, a treasure trove that will keep the teams busy for the coming years.

Annotated version of the eROSITA First All-Sky image. Several prominent X-ray features are marked, ranging from distant galaxy clusters (Coma, Virgo, Fornax, Perseus) to extended sources such as Supernova Remnants (SNRs) and Nebulae to bright point sources, e.g. Sco X-1, the first extrasolar X-ray source to be detected. The Vela SNR is to the right of this image, the Large Magellanic Cloud in the bottom right quadrant, the Shapley supercluster in the upper right (though not easily visible in this projection).

False colour image of the Large Magellanic Cloud (LMC), our next neighbour galaxy. Covering a larger area than the first light image from eROSITA by a factor of about one hundred, the astronomers are now able to explore the entire galaxy, in particular its X-ray binary population as well as the rich structures seen in the diffuse emission arising from the hot phase of the interstellar medium. Among the brightest sources are X-ray binaries, which were the first to be discovered in the LMC already at the beginning of X-ray astronomy as well as supernova remnants, which can be resolved by eROSITA.

In the annotated image above, the four brightest X-ray sources in the LMC region are marked (LMC X-1 to 4). Also visible are numerous Supernova Remnants (SNR) and many foreground stars, the brightest of which is marked, too. On the bottom right, a zoom is shown into the central region of the LMC, which was the first image captured by eROSITA with its seven telescopes back in October 2019.  

Due to its size and close distance to Earth, the "Vela supernova remnant" which is shown in this picture is one of the most prominent objects in the X-ray sky. The Vela supernova exploded about 12000 years ago at a distance of 800 light-years and overlaps with at least two other supernova remnants, Vela Junior (in the picture seen as bluish ring at the bottom left) and Puppis-A (top right). Vela Junior was discovered just 20 years ago, although this object is so close to Earth that remains of this explosion were found in polar ice cores. All three supernova explosions produced both the X-ray-bright supernova remnants and neutron stars, which shine as intense X-ray point sources near the centres of the remnants. The quality of the new eROSITA data of this "stellar cemetery" will give astronomers many exciting new insights into the physical processes operating in the hot supernova plasma as well as for exploring the exotic neutron stars.

The bright blue point source in the middle of the image is the Vela pulsar, Vela Junior is the bluish ring to the bottom left, also with a pulsar at the centre. The Puppis pulsar is not resolved by eROSITA.

The Shapley supercluster of galaxies is one of the most massive concentrations of galaxies in the local universe at a distance of about 650 million light-years (z~0.05). Each of the dozen extended structures is itself a cluster of galaxies, consisting of 100s to 1000s of individual galaxies, each denoting an intersection of filaments making up the large-scale structure in the Universe. This image spans 16 degrees across the sky (about 30 times the size of the full moon), which translates into about 180 million light-years across at the distance of the Shapley supercluster. The images on the left show a zoom of the the most massive clusters in the Shapley supercluster.

In the image above all the most prominent galaxy clusters and groups, detected by eROSITA as extended X-ray sources, are marked with their astronomical names. The largest ones are drawn from the Abell catalogue of clusters, hence the 'A's in their names.

The glowing ring in the centre of this 7 degrees wide image was discovered after eROSITA scanned over this sky region in February 2020. The ring is caused by X-rays scattered on a dust cloud in the plane of the Milky Way. The origin of the radiation is the faint blue object in the centre of the ring, assumed to be a black hole circled by a companion star.  One year before the eROSITA observation,   a massive outburst of this object was recorded by other X-ray telescopes; for a few weeks it was more than 10000 times brighter than at present. On its thousands years travel, a tiny fraction of the burst radiation was scattered by a dust cloud; the scattered X-rays arrived one year after the direct radiation from the burst, just like an echo. This extra travel causes the apparent ring which will grow with time before becoming too faint to be observable.  A few dust scattering rings were observed in the past, but with an angular diameter of more than twice the size of the full moon the new structure is by far the largest of its kind. Modelling of the ring may help to measure a precise distance to the black hole X-ray binary.

The pale blue dot at the center of the ring is the X-ray binary MAXI J1348-630, which went into outburst in February 2019. On the top left, the red source is the star beta Centauri, one of the brightest stars in the southern sky.

The Carina Nebula and its interstellar environment seen with eROSITA (red: 0.2 - 0.5 keV, blue: 0.5 - 1.0 keV, green: 1.0 - 2.0 keV). The Carina Nebula is one of the largest diffuse nebulae in the Milky Way and hosts a large number of massive, young stars. The brightest of the stars (also in X-rays) is Eta Carinae, a binary system consisting of two massive stars, in which the winds of the stars collide. The bluish emission seen left of the nebula is X-ray emission from an open cluster of stars.

eROSITA Factsheet

eROSITA Telescope:

Start of the project: 1 April 2007 (DLR funding approved)

SRG Mission adoption: 18 August 2009 (contract signed between DLR and Roscosmos)

Mirror modules: 7 (with 54 mirror shells each)

Mirror shell smoothness: ~0.3 nm

Cameras: 7 pnCCDs with 384 x 384 pixels each

Field of view: ~ 1 degree in diameter

Operating temperature: around -85°C

Energy range: 0.2-8 keV

Launch: 13 July 2019

Start of camera commissioning: 22 August 2019

Start of operation of all 7 cameras: 13 October 2019

Orbit: Halo orbit around L2

Spacecraft: Spectrum-Roentgen-Gamma (together with ART-XC telescope)

 

eRASS-1: First SRG/eROSITA All-Sky Survey

Start: 13 December 2019

Completed:  11 June 2020

Days to complete all-sky image: 182

Data downloaded (eROSITA only): ~165Gb

Number of commands issued (eROSITA only): >15000 (TBD)

Photons collected: ~400 million (in the energy range 0.12-5 keV)

Average exposure: 180 seconds

Sources detected: 1.1 Million

Approximate break-down of sources:

  • 77% Active Galactic Nuclei
  • 20% stars with strong, magnetically active hot coronae
  • 2 % clusters of galaxies
  • others: bright X-ray binaries, supernova remnants, extended star forming regions, transient (e.g. Gamma-Ray Bursts)

Other Interesting Articles

Go to Editor View