Why can radio telescopes observe distant stars?

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Why can radio telescopes observe distant stars?

2018-09-25 10:25:35 151 ℃

On September 25, 2016, the world's largest single-caliber spherical radio telescope was visually called China's "Eye of Heaven". Today, let's talk about why radio telescopes can observe distant stars!

In 1932, a US radio engineer, Jansky, used a short-wave receiver and a directional antenna. When studying long-distance communication, a strange interference was discovered. The magnitude of this disturbance gradually changes over the course of 24 hours, and it sounds like a thunderstorm caused by lightning interference, but a continuous "beep" sound. Even more strange is that whenever the antenna points in a certain direction of space, the interference becomes maximum. It was later discovered that this direction is exactly the direction of the center of the Milky Way, where the stars are the most dense. It turned out that this is the first time humans have received radio waves from celestial bodies.

This discovery has aroused great interest. With the development of radio technology, radio waves from the sun, moon, planets, galaxies, supernova explosions and nebulae, interstellar gas were discovered. The application of radio technology has injected new blood into ancient astronomy, creating a new branch of astronomy - radio astronomy.

Before the invention of optical telescopes, many astronomers have made many valuable observations with the naked eye. But our eyes can only see visible light, but can't see radio waves, so radio astronomy is associated with radio telescopes since its birth.

The radio telescope consists of a directional antenna and a highly sensitive receiver. The antenna acts like a lens or mirror of an optical telescope, which converges the radio waves emitted by the celestial body. The receiver acts like our eyes or photographic film, which converts, amplifies, and records the radio waves collected by the antenna.

The world's largest optical telescope is now a 6-meter reflective telescope, which is almost the pinnacle of a single-lens optical telescope. With it we can see celestial bodies about 100 billion light-years away.

The radio telescope is less affected by the Earth's atmosphere and can be observed day and night. Modern technology allows us to make antennas that are much larger in diameter than optical telescopes. At present, the world's largest fully mobile radio telescope has a diameter of 100 meters, which is more than 16 times that of the world's largest optical telescope. In addition, with the development of radio technology, people have made extremely sensitive receivers. In order to make the radio telescope more powerful, radio astronomers also use multiple antennas together. For example, the recently constructed US "Very Large Array" radio telescope consists of 27 parabolic antennas with a diameter of 25 meters arranged in three shapes each of 21 kilometers long. When it was completed in 1981, it was the most powerful radio telescope in the world. It can be used to find signals from a 1 kW transmitter tens of billions of kilometers away. Because radio telescopes have more power than optical telescopes, we are able to find celestial bodies that are tens of billions of light years away from us.

The ability of many celestial bodies to emit radio waves is much greater than the ability to emit light waves. For example, the famous Cygnus A radio source, its ability to emit radio waves is 100 billion times stronger than the sun. Therefore, many distant objects that cannot be seen with optical telescopes may also be discovered by radio telescopes.

In addition, there are many dust clouds in the universe, which greatly weaken the light emitted by distant celestial bodies. The radio waves emitted by the celestial body, because of its wavelength is much longer than the wavelength of light, are much less affected by these dust substances.

For these reasons, radio telescopes can make full use of its powerful power, allowing us to use it to discover more distant and weaker objects and explore the mysteries of the depths of the universe.