China will launch the "Einstein Probe Satellite" to survey and locate black holes in the universe

Recently, the Chinese Academy of Sciences announced that my country plans to launch an Einstein probe satellite by the end of 2023, which is expected to capture the first ray of "light" from a supernova explosion, help search for and accurately locate the source of gravitational waves, and discover more distant, fainter celestial bodies and fleeting mysterious phenomena in the universe. What type of satellite is this? What are its unique tricks? Why is it named after Einstein?

01. An X-ray scanner in space

The Einstein Probe satellite is an X-ray space observatory .

When it comes to X-rays, you will definitely think of the instrument used for chest X-rays during physical examinations, which can take pictures of the chest cavity through clothes. In fact, X-rays are also a kind of electromagnetic waves. Many high-energy celestial bodies in the universe will produce electromagnetic radiation in the X-ray band. For example, when a star reaches the end of its life, a supernova explosion, two neutron stars merge, and a black hole accreting surrounding matter will also produce strong X-ray signals. Even our sun is constantly producing electromagnetic waves in the X-ray band.

It can be said that in addition to being used for physical examinations in daily life, the X-ray band can also be used to conduct "physical examinations" on high-energy celestial bodies that produce X-rays . By analyzing the X-ray signals produced by high-energy celestial bodies, the physical processes of high-energy celestial bodies can be characterized, thereby enhancing our scientific understanding of the formation and evolution of the universe.

Therefore, X-ray detection is very important in the field of astronomy. However, our atmosphere absorbs X-ray signals, so X-ray observatories are built in space. In 1996, the United States launched the Chandra X-ray Observatory, and in 2017, my country launched the Insight-HXMT hard X-ray modulation telescope, which made important contributions to the detection of the mysterious X-ray universe.

High-energy celestial bodies in the universe also emit X-rays. Image source: Tuchong Creative

02. Ingenious design that combines field of view and sensitivity

When it comes to astronomical observations, we often hope to be able to see as wide a range as possible and the target as dark as possible. This is reflected in the design indicators, that is, we hope that the field of view of the telescope is as large as possible and the sensitivity is as high as possible. This way, we can quickly see the entire universe and monitor the dynamic changes in the universe in real time.

However, for telescope design, field of view and detection sensitivity are a pair of contradictory indicators . It is often difficult for a telescope with a large field of view to achieve high detection sensitivity, while a telescope with high detection sensitivity often finds it difficult to achieve large field of view detection, just like you can't have your cake and eat it too. The trick of the Einstein Probe satellite is to achieve both a large field of view and high sensitivity detection at the same time . Its core payload is a lobster-eye telescope .

Biologists discovered early on that lobsters' eyes are different from those of other animals. They are made up of numerous microscopic tubes in the shape of square holes. The walls of the tubes are smooth and point to the same center. This structure allows light from all directions to be reflected in the small square holes and converge on the retina.

In 1979, American scientists got inspiration from this and proposed to simulate lobster eyes to make telescopes, so that X-rays can be focused and imaged through reflection. However, this idea was not realized for a long time after it was proposed. It was not until the micro-machining technology was improved that scientists gradually developed microporous lobster eye lenses, which were covered with small square holes as thick as hair.

The National Astronomical Observatory began developing the LobsterEye X-ray imaging technology in 2010, and after years of hard work, it finally achieved a breakthrough. The field of view of X-ray focusing telescopes made by other methods is about the size of the moon as seen from Earth, while the LobsterEye telescope can cover an area of ​​the sky about the size of 1,000 moons . Twelve such telescopes will be installed on the Einstein Probe satellite, with a field of view of about 10,000 moons.

03. A powerful assistant for astronomical observation

The unique design of the Einstein Probe Satellite enables it to detect a large number of unpredictable X-ray astronomical events in the universe, including the merger of two neutron stars that produces gravitational waves. The Einstein Probe Satellite can cooperate with ground-based gravitational wave detection instruments such as LIGO to accurately locate gravitational wave events . The Einstein Probe Satellite can also detect X-ray signals emitted by black holes capturing stars, conduct a census and locate black holes in the universe , and answer scientific questions such as whether black holes are common in the universe.

Gravitational waves and black holes are the two brightest pearls in the crown of Einstein's general theory of relativity, so the naming of the Einstein Probe Satellite is also a tribute to the scientific giant Einstein.

The Einstein Probe Satellite is a satellite of my country's strategic leading science and technology project for space science. The previously launched "Kuafu-1", "Huiyan", "Wukong" and "Mozi" satellites are all members of the large family of space science satellites. Looking to the future, Chinese scientists have planned five major space science frontier exploration roadmaps, namely "extreme universe", "space-time ripples", "sun-earth panorama", "habitable planets" and "space objects", to contribute China's strength to understanding the mysteries of the universe.

This article is a work supported by Science Popularization China Starry Sky Project

Author: Li Mingtao

Reviewer: Han Wenbiao (Researcher at Shanghai Astronomical Observatory, Chinese Academy of Sciences)

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.