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eROSITA telescope to open wide window on the Universe

One of the two telescopes aboard the Spektr-RG observatory was developed at the Max Planck Institute for Extraterrestrial Physics, MPE, in Germany under the leadership of Peter Predehl. Known as extended ROentgen Survey with an Imaging Telescope Array, or eROSITA, the instrument features seven telescopes designed to capture X-ray radiation emitted from across the Universe, giving the Spektr-RG observatory its unique wide field of view into high-energy sources in the cosmos.

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eROSITA at a glance (as of 2019):

Mirror structure
Sensitivity range
approximately 0.2 - 12 keVolts
Field of view
60 angular seconds
Angular resolution
18 arc seconds
795-815 kilograms
Instrument dimensions
1.3 by 2.6 meters
Power consumption
405 Watts
Number of mirror modules
Number of mirror shells per each module
Mirror shell length
300 millimeters
Mirror shell diameters
76-358 millimeters
Focal length
1,600 millimeters
Mirror material
Mirror coating
Pn-CCD, Silicon
Detector size
28.8 by 28.8 millimeters
Detector pixel size
384 by 384 pixels
Detector operating temperature
-95 degrees C

How eROSITA works

The creators of the mirror system for the eROSITA telescope built up on the experience gained during the development and operation of previous orbital X-ray observatories, first of all, the European XMM-Newton project. The development of the eROSITA telescope was funded by the German Aerospace Center, DLR, and by the Max Planck Institute.

Each of the seven telescopes comprising the eROSITA instrument contains a system of 54 nested mirrors, forming a conical tubular structure. Such an unusual design is necessary for gathering and focusing X-rays, which have the property of bouncing of the mirrors under a very sharp angle.

At the focal plane of each telescope module, there is a dedicated camera containing charge-coupled device, CCD, detectors, which were manufactured from highly pure silicon at the semi-conductor lab of the Max Planck Institute. Unique detectors of this type were flight-proven aboard the XMM-Newton observatory and on the Spirit and Opportunity Mars rovers, among other spacecraft.

To maximize the sensitivity of the cameras aboard eROSITA, they will be kept at -95 degrees C during the mission with the help of a special passive cooling system employing heat pipes and radiators.

A pair of star trackers of the Spektr-RG spacecraft attached to the eROSITA telescope will be used for the precise pointing of the instrument at its targets.


Front (left) and aft views of the eROSITA telescope.

What is it for?

According to Max Planck Institute, the clustered design of the eROSITA telescope provides a unique combination of collecting area, field of view and resolution for an X-ray instrument. For example, eROSITA will be able to peer 30 times deeper into space than did the previous-generation ROSAT orbital observatory.

The eROSITA telescope cluster will scan the entire sky with unprecedented spectral and angular resolution and imaging sources of X-rays emitting in a wavelength from around 0.2 to 10 kiloelectron volts.

This new capability will be used for observations of the largest gravitationally bound entities in the Universe, such as galactic clusters, a kind of islands in the Universe composed of thousands of galaxies, which themselves contain up to several hundred billion of stars.

The telescope will observe hot intergalactic medium of 50,000 to 100,000 galactic clusters, as well as the hot gas in filaments between the clusters.

Detailed observations of these colossal structures might help unlock mysteries of the evolution of the Universe and improve understanding of key cosmological phenomena, such as dark energy, an enigmatic force believed to be driving the continuing expansion of the Universe despite the counteracting force of gravity. The accuracy of the eROSITA telescope should allow to test various theoretical models explaining dark energy, Max Planck Institute said.

The instrument was reported to be able to systematically observe all obscured accreting black holes in near-by galaxies and to detect up three million new distant active galactic nuclei hiding super-massive Black Holes.

Data from eROSITA will also allow detailed studies into the physics of galactic X-ray sources, such as pre-main sequence stars, remnants of supernovas and X-ray binaries. As many as 700,000 stars of all kinds will be detected by the instrument, if everything works as planned.


A front view of the eROSITA telescope with seven mirror assembies.

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Article and illustration by Anatoly Zak; Last update: May 9, 2019

Page editor: Alan Chabot; Last edit: April 22, 2018

All rights reserved

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A depiction of eROSITA bundle circa 2011. Credit: Max Planck Institute


A cutaway view of the eROSITA telescope. Credit: Max Planck Institute


A structural component of the eROSITA telescope. Credit: Max Planck Institute


An individual mirror shell of the eROSITA telescope. Credit: Max Planck Institute


A mirror module. Credit: Max Planck Institute


A CCD module for the eROSITA telescope. Credit: Max Planck Institute


An X-ray baffle. Credit: Max Planck Institute


A filter wheel. Credit: Max Planck Institute

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