The Chinese Academy of Sciences (CAS) Einstein Probe is set to launch in January 2024. Equipped with a new generation of high-sensitivity and very wide-field X-ray instruments, this mission will survey the sky and search for powerful bursts of X-ray light coming from mysterious celestial objects such as neutron stars and black holes.
Einstein Probe is a CAS-led collaboration with the European Space Agency (ESA) and the Max Planck Institute for Extraterrestrial Physics (MPE), Germany.
In return for its contribution to the development of this mission and the definition of its scientific objectives, ESA will receive access to 10% of the data generated by the Einstein Probe observations.
“Thanks to its innovative design, Einstein Probe can observe large parts of the sky at a glance. In this way, we can discover many new sources while at the same time studying the behavior of X-ray light coming from known celestial objects over long periods,” says Eric Kulkers, ESA’s Einstein Probe project scientist. “Space is our only laboratory for studying the most energetic processes. Missions like Einstein Probe are essential to improve our understanding of these processes and to learn more about fundamental aspects of high-energy physics.”
Keep a close eye on the X-ray sky
Unlike the stars that dot our night sky and reliably mark the constellations, most cosmic objects that glow in X-rays are highly variable. They constantly lighten and darken, and in many cases appear briefly before disappearing for long periods (then called transients) or forever.
Fueled by turbulent cosmic events, X-ray light from astronomical sources is highly unpredictable. Yet it carries fundamental information about some of the most enigmatic objects and phenomena in our Universe. X-rays are associated with collisions between neutron stars, supernova explosions, matter falling onto black holes or hyper-dense stars, or high-energy particles ejected from discs of flaming material orbiting such exotic and mysterious objects.
Einstein Probe will improve our understanding of these cosmic events by discovering new sources and observing the variability of X-ray glowing objects across the sky.
The ability to routinely spot new X-ray sources is fundamental to advancing our understanding of the origin of gravitational waves. When two superdense massive objects like two neutron stars or black holes collide, they create ripples in the fabric of spacetime that travel cosmic distances and reach us. Several detectors on Earth can already register this signal, but often cannot locate the source. If neutron stars are involved, such a “cosmic collapse” is accompanied by a huge burst of energy in the light spectrum and especially in X-rays. By enabling scientists to rapidly probe these short-lived events, Einstein Probe will help us identify the origin of many of the gravitational wave pulses observed on Earth.
Lobster eyes in space
To achieve all of its scientific goals, the Einstein Probe spacecraft is equipped with a new generation of instruments with high sensitivity and the ability to observe large areas of the sky: the Wide Field X-ray Telescope (WXT) and the Follow-up X-ray Telescope (FXT).
The WXT has an optical modular design that mimics lobster eyes and uses innovative Micro Pore Optics technology. This allows the instrument to observe 3,600 square degrees (almost a tenth of the celestial sphere) in a single frame. Thanks to this unique capability, the Einstein probe can closely observe almost the entire night sky in three orbits around Earth (each orbit takes 96 minutes).
New X-ray sources or other interesting events spotted by WXT are then targeted and studied in detail with the more sensitive FXT. Most importantly, the spacecraft will transmit a warning signal to earth to trigger other telescopes on Earth and in space operating at other wavelengths (from radio to gamma rays). They will quickly target the new source to collect valuable multi-wavelength data, thus enabling a more in-depth study of the event.
ESA played an important role in the development of Einstein Probe’s science instruments. Provides test and calibration support for WXT’s X-ray detectors and optics. ESA developed the mirror assembly of one of FXT’s two telescopes in collaboration with MPE and Media Lario (Italy).
The FXT mirror is based on the design and technology of ESA’s XMM-Newton mission and the eROSITA X-ray telescope. MPE contributed the mirror assembly for the other FXT telescope and developed the detector modules for both FXT units. ESA also provided the system for deflecting unwanted electrons from the detectors (the electron deflector).
During the mission, ESA ground stations will be used to help download the data from the spacecraft.
ESA’s fleet of high-energy missions
ESA has a long history of developing high-energy astronomy. XMM-Newton and Integral have been exploring the X-ray and gamma-ray universe for more than two decades, leading to major advances in the field. ESA is also involved in the X-ray Imaging and Spectroscopy Mission (XRISM), led by the Japan Aerospace Exploration Agency (JAXA) in collaboration with NASA, which launches in the summer of 2023.
“The capabilities of the Einstein probe are highly complementary to the in-depth studies of individual cosmic sources enabled by the other missions,” notes Eric. “This X-ray surveyor is also the ideal precursor to ESA’s NewAthena mission, which is currently under investigation and will be the largest X-ray observatory ever built.”
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