"Lobster eyes" in sky, a major breakthrough in China's space science technology

BEIJING, Jan. 10 (Xinhua) -- China's newly launched X-ray astronomical satellite Einstein Probe (EP) has adopted a cutting-edge technology inspired by the functioning of lobster's eyes, marking a breakthrough for China in the field of space science.

The EP has been built by an international collaborative effort led by China. The European Space Agency and the Max Planck Institute for Extraterrestrial Physics in Germany jointly participated in the development of the project. The French Space Agency provided VHF (very high frequency) antennas for the EP.

Shaped like a double-pistiled lotus flower with 12 petals blooming in space, the EP is designed to detect outbursts in the universe at X-ray wavelengths. Each "petal" is a special X-ray telescope. On each "petal" there are 36 microporous imagers, each containing nearly one million square holes thinner than a single strand of hair.

Yuan Weimin, the principal investigator of the EP, said that making an X-ray telescope capable of focusing and wide-field imaging is very tricky.

"That's because X-ray photons have very short wavelengths and high energies. They are extremely penetrating and easily interact with atoms, making it difficult to focus them through refraction or reflection like visible light," said Yuan, who is also a researcher at the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC).

"If you throw a stone into the water, the stone is too heavy and will sink to the bottom, but if you throw the stone against the water at a very small angle, the stone can bounce off the surface. Similarly, if an X-ray forms a very small angle with a reflective surface, then it is possible for the X-ray to form a reflection. This reflection can then be used to focus and create an image," Yuan said.

In this regard, scientists have taken inspiration from the unique eye structure of lobsters, first proposed by American astronomer Roger Angel.

Biologists discovered early on that the lobster's eye is different from that of other animals. Lobster eyes are made up of numerous tiny square tubes, which point to the same spherical center. This structure allows light from all directions to reflect in the tubes and converge on the retina. This gives the lobster a large field of view. Scientists simulated the lobster eye to create a telescope that detects X-rays in space.

Through cooperation with other organizations, the X-ray Imaging Laboratory of NAOC began the research and development work on lobster-eye X-ray imaging technology in 2010.

"After years of efforts, we finally made a technological breakthrough," said Zhang Chen, assistant to EP's principal investigator.

The team carried out the validation testing of the technology on the telescope Lobster Eye Imager for Astronomy (LEIA) -- a pathfinder of the EP instrument -- which was launched in July 2022. The tests revealed the world's first batch of large-field X-ray snapshots of the sky captured by the LEIA.

According to Zhang, the previous X-ray telescopes only had a field of view roughly the size of the Moon as seen from Earth, while the field of view of the EP could be as large as about 10,000 Moons.

For the first time, large field-of-view whole-sky monitoring and X-ray focusing and imaging have both been realized at the same time, which allows for efficient monitoring of the X-ray changes of celestial bodies, Zhang added.

Moreover, the EP also pioneers in installing CMOS sensors, which can process with good spectral resolutions and fast speed. "We have realized the application of CMOS sensors to X-ray astronomical observations in space. It is an innovation in X-ray astronomy detection technology," said Ling Zhixing, a scientist of the NAOC.

The EP, launched on Tuesday from the Xichang Satellite Launch Center in southwest China's Sichuan Province, once again bolstered the country's fleet of space science satellites in the vast expanse of space, which includes the Dark Matter Particle Explorer, the Quantum Experiments at Space Scale, the Hard X-ray Modulation Telescope, and the Advanced Space-based Solar Observatory.

"While Europe, the United States and Japan have been developing space science for more than half a century, space science in China is still in its initial stage of development. However, we have made rapid progress over the past 20 years and have entered the international forefront in certain fields," Yuan added.

The lobster-eye telescope technology will revolutionize monitoring of the X-ray sky, and shows the strong scientific potential of the Einstein Probe mission, said Paul O'Brien, head of Astrophysics, School of Physics and Astronomy at the University of Leicester.