All-rounder “wisdom eye”
On June 15, 2017, my country’s first X-ray astronomical satellite was launched into the sky, running in a near-Earth circular orbit of 550 kilometers. It is the “Huiyan” satellite, the full name of which is “Hard X-ray Modulation Telescope Satellite” (HXMT for short). Since then, the “Huiyan” satellite has begun to stare at the dark starry sky, not to look at the stars, but to detect X-rays that are invisible to the naked eye.
With the deepening of human exploration, the research of astronomy has long been no longer limited to the traditional visible light band, but has entered the era of full-wave astronomy that can observe the entire band of electromagnetic waves. The full spectrum of electromagnetic waves includes not only visible light, radio waves, infrared, ultraviolet, but also high-energy X-rays and gamma rays. In recent years, these high-energy electromagnetic waves have been found in many intense celestial activities and become the focus of current research. It can be said that the observation era of high-energy astronomy has come, and the “wisdom eye” is the product of X-ray observation in this era.
To observe X-rays, X-rays must first be focused and imaged. When light encounters the mirror disk, it will be reflected and focused. However, the X-ray energy is so great that it can pass through the lens disk without reflection, so it cannot be focused. To focus the X-ray image, it needs to glank at the mirror disk at a very low angle. Just like a ball, when it hits the wall from the side, it bounces off the other side of the wall, which achieves focusing. Therefore, X-ray telescopes are called “grazing telescopes”.
X-ray telescopes designed according to this principle have a seemingly strange appearance: many very thin tubes pointing into space. When X-rays enter the tube, they hit the tube wall, collide and then reflect, and finally grazing onto the mirror surface to focus and image on the mirror surface.
”Smart Eye” is not an X-ray telescope, but an X-ray satellite that includes three sets of X-ray telescopes. The three sets of X-ray telescopes receive different rays of low, medium and high energies respectively. Among them, the high-energy X-ray telescope is responsible for receiving X-rays above 20 keV, and the low-energy X-ray telescope is responsible for receiving X-rays with energy below 10 keV. Therefore, “wisdom eye” has 3 kinds of abilities at the same time, although these functions are not powerful, but it is a generalist.
“Heroes” with “wisdom eyes”
The stars in the universe can emit light and heat, and they are huge nuclear reactors. However, they will go to twilight, to death. When the hydrogen is exhausted, the entire star can no longer continue to burn, so a supernova explosion will turn it into a white dwarf, neutron star or black hole, which are all dense stars.
Dense stars are not only dense, but also have super-strong magnetic fields. Strong magnetic fields produce high-energy cosmic rays that are much more energetic than photons.
When a star is alive, it shines like a heroic warrior, and after it dies, it becomes an undead hero, and the “wisdom eye” satellite specializes in this “hero”. “Smart Eye” turns on the search mode, and you can find the sky area that emits X-rays, and distinguish which one is the most powerful.
In August 2020, the “Huiyan” satellite aimed the observation target at the pulsar GRO J008-57, and the magnetic field strength on the surface of the pulsar was measured to be 1 billion Tesla by direct measurement. This is very reliable data and the strongest magnetic field known to man at the time. A pulsar is a neutron star that emits electromagnetic waves from its poles, and its magnetic field is extremely strong. The magnetic field is invisible, but it exists. When a wire with a current strength of 1 amp is placed around a magnetic field, the magnetic field acts on it. If the force is 1 Newton, then the strength of the magnetic field is called “1 Tesla”. The strength of the magnetic field at 1 billion Tesla is beyond our comprehension. If the wire is placed in this magnetic field, the wire must be twisted into a twist, or it will no longer exist.
“Huiyan” obtained the surface magnetic field strength of pulsar GRO J008-57 by direct measurement method to be 1 billion Tesla
Although there are a lot of X-ray observation equipment abroad and a lot of information from space radio radiation, it has not broken the observation record of the “Wisdom Eye” satellite, and the record is broken by itself. In July 2022, “Smart Eye” aimed at the Swift J0243.6+6124 neutron star again. This is not an ordinary neutron star, but a double neutron star. The observations of the “Huiyan” satellite show that the energy of the neutron star is very high, up to a cyclotron absorption line of 146 kiloelectron volts, and the corresponding magnetic field exceeds 1.6 billion Tesla, which is the strongest known magnetic field in the universe. Swift J0243.6+6124 is a double neutron star with an accretion disk between the two neutron stars. The “Huiyan” satellite may measure the magnetic field of the accretion disk near the neutron star.
Previously, astronomers have discovered a special class of neutron stars, outside the Milky Way, where X-rays are exceptionally bright. While scientists have long suspected that a super-strong magnetic field exists there, there is no direct measurement evidence. This speculation was confirmed by the “wisdom eye” satellite, and the real “hero” was found.
“Wisdom Eyes” look in all directions
Due to the interference of the earth’s atmosphere, X-rays cannot be received on the ground, and it is generally difficult to send telescopes into space. Therefore, the history of X-ray telescopes is only a few decades old. In 1962, the United States launched a sounding rocket with a detector that discovered the first source of cosmic rays: Scorpio. After that, X-ray astronomy was born. In the past ten years, a large number of high-energy physical phenomena have been discovered, which has further stimulated people’s enthusiasm for the development of X-ray telescopes. Due to the extremely strong penetrability of X-rays, it is difficult to design and manufacture X-ray telescopes that can image. The most powerful of these is the Chandra X-ray Space Telescope in the United States, which takes X-ray pictures of celestial objects that are almost comparable to those taken by optical telescopes.
my country’s X-ray telescope has only started for more than ten years. Although the ability of X-ray imaging to take pictures is far from enough, it still has many unique advantages. First of all, my country’s X-ray telescope has a wide energy range, and the energy can be observed from high to low. Secondly, it has a wide observation area and can achieve rapid sky surveys. The “Huiyan” satellite can turn its line of sight to any direction at will in space, and it is unobstructed in all directions. So far, it has achieved many achievements.
On August 17, 2017, this was the time when humans first discovered gravitational waves. At that time, the “Huiyan” satellite had just been successfully launched, and it was still in the test practice period, but it was fortunate to monitor the world’s first gravitational wave event of the merger and collision of two neutron stars, and made a reasonable judgment on the radiation properties.
“Smart Eye” not only observed the radio storm within the predicted time, but also gave an accurate location
“Smart Eye” is not an X-ray telescope, but an X-ray satellite including 3 sets of X-ray telescopes
Fast radio bursts are a strange phenomenon discovered in recent years. This phenomenon refers to the sudden appearance of X-rays in the sky, staying for only 1 second, and then disappearing silently. No one knows where it came from, and no one knows if it will ever appear again. In the past two years, it has been found that there are repeating radio bursts, and the time of the next burst can be predicted. “Smart Eye” not only observed the radio storm within the predicted time, but also gave accurate positioning. This location lets people know that the fast radio burst FRB 200428 originated from the magnetar SGR J1935+2154. The discovery of fast radio bursts produced by the eruption of magnetars has become one of the top ten scientific achievements recognized in 2020.
The Wisdom Eye satellite also discovered the relativistic jets closest to the black hole. In a pair of black hole binaries, some plasmas are escaping the black hole’s gravitational field at high speed, which has also been observed by the “wisdom eye”. Moreover, the “wisdom eye” also observed the evolution of the corona for the first time in a black hole binary star.
In addition, “Huiyan” has carried out X-ray pulsar navigation experiments, and the positioning accuracy is within 10 kilometers, which provides the basis for future interstellar navigation.
With the help of the observation results of “Huiyan”, relevant researchers in my country have published more than 120 papers in total, involving gravitational waves, gamma-ray bursts, fast radio bursts, black holes and neutron stars. important contributions to physics.
Although the design life of “Huiyan” is only 4 years, on June 15, 2022, it has passed its 5th birthday, but its various performances are still good at present, scientists hope that it can be retired later and re-established achievement.