Radio astronomy and giant antennas

The seventeenth century was an era of astronomy thanks to the invention of a telescope by Galilée and the great scientific achievements of Kepler and Newton on gravity. Astronomy has taken a long step from Astrology to become a natural science. Physics begins when astronomers explain the movement of celestial bodies. After they explore solar energy and stars and the origin of the Universe.

Antenna in BIMA interfering radio system of Berkeley University (California, USA).In the sky is the center of the Milky Way (Photo: vietsciences)

Radio astronomy and antennas to receive signals emitted by celestial bodies on physical and chemical conditions in a celestial body, we must not only observe the radiant radiation but also receive radiation in other wavelengths of electromagnetic spectrum, such as X-rays, ultraviolet, infrared and radio. Each type of radiation is emitted by a particular physical mechanism. For example, observing visible radiation to study stars and ionic gas in galaxies. The dust component only emits infrared radiation. Molecules in dark clouds in interstellar environments emit radio radiation. The cosmic background radiation 2.7K is the strongest on the midst of stars emitting the radio radiation of the Sun without causing diffraction of celestial bodies. Moreover, the solar radiation of the Sun does not interfere with the celestial bodies. Radiation emitted on centimeter radio waves is not hampered by rainwater, so the observation work does not depend on the weather.

In 1932, Mr. Jansky worked at the Telephone Company of America Bell accidentally discovered the first radio radiation from the Universe. It is radiation emitted by the Milky Way. After the Second World War, radio astronomy began to develop thanks to the technology of creating radar antennas and radio signal receivers. The intensity of radio radiation obtained from celestial bodies into telescopes is only about one millionth of a billionth ( ^10-18 ) W, which is extremely small compared to the intensity of a commonly used 60W light bulb. So the astrophysics antennas must be very large and the receiver must be very sensitive to "catch" each photon. Astronomers have obtained solar system radio radiation sources, stars, nebulae in the Milky Way, distant galaxies and quasars.

Thanks to the radio-monitoring facilities, there have been unexpected findings such as punxa, a kind of spinning and radiation like a lighthouse. A great achievement of radio astronomy discovered in 1965 is the cosmic background radiation. It is an important factor that reinforces the theory of big explosions creating the Universe. Several years later, radio astronomers found in the Milky Way many molecules including complex organic molecules. But this organic molecule is a sample of amino acids in protein (protein), a characteristic of life. The discovery of molecules in the Universe is a decisive event in the study of dark clouds and densities not previously observed.

Telescopes used in radio astronomy are radar-like antennas that can track celestial bodies rotating in the sky. The signal emitted from the Celestial bodies is obtained in a radio telescope similar to the noise heard in a radio. We have to produce receivers and signal amplifiers that use superconducting diodes with very little noise to highlight the signals of the celestial body. Signaling units must be placed in a chilled vessel with Helium gas to reduce the noise emitted by the device. The data is processed by computer and the radio signal turns into a drawing image on the screen. In order for the Thien image to be clearly shown on the screen, astronomers must "take a picture" of the celestial body for a long time by watching the Heavenly body for hours. The computer is also used to control telescopes that automatically turn to the aiming direction.

VLA antenna system (Photo: public)

Radio radiation has a short wavelength, millimeter wavelength, absorbed by water vapor in the atmosphere. Millimeter telescopes are often placed on high mountains in dry places like observation lenses in the visible field. Observations on long wavelengths, centimeter waves and meters are often affected by artificial diffraction such as radar and satellite television systems. Radio observatories are often located in remote locations away from the industrial center. An International Commission was established and dedicated a number of electromagnetic street waves for radio astronomers. These spectral regions have many molecular lines that astronomers often observe. In principle, no one is allowed to transmit wavelengths in this sacrosanct spectrum. However, the fact that there is still some diffraction of the International Commission's decision is not fully respected, in part because the cosmic radiation receivers are increasingly sensitive.

Radio telescope with a very large diameter from 10-300m. Currently there are about 40 radio telescopes in the world. Because the antenna face does not need to be as smooth as the mirror surface of the lenses used in the variable wave region, the large antenna is easier to make than the larger mirror surface. Furthermore, the resolution limit (the ability to separate small details) on radio wavelengths is poorer on the visible wavelength. If we want to have the telegraph limit of resolution similar to the resolution limit of a 10m mirror in the variable region, then the antenna size must be 10km. With modern technology, we cannot build such a giant antenna. However, we can achieve a good resolution limit as a giant antenna 10km by using 2 small antennas located 10km apart and operating in correlation with this method is mixing the signal obtained from each antenna together. According to the optical laws, signal mixing increases the resolving power of lenses.

In fact, an array of antennas is often used to further increase the sensitivity of the interference system. The VLA antenna system (Very Lara Array) consists of 27 antennas, each with a diameter of 25m, located in the state of Mexico - the United States operates on cm and mm wavelengths. The antennas of VLA system are arranged according to the Y-shaped orbit. The maximum distance between the antennae is about 35km. VLA's interfering system has a resolution limit equivalent to an antenna with a diameter of 35km and is capable of separating small details with candles at least 4km away. The farther away the distance between the antennas is, the more clearly the details of the celestial body. Each year more than 500 astrophysicists around the world use VLA antennas. Currently there is an international interference network that uses about a dozen antennas thousands of kilometers apart, located on continents to have very small resolution limits. There are projects from Russia, Japan and the European community that plan to launch orbiting antennas around the Earth to increase the distance between the antennas used to observe galaxies and distant constellations that shake in extremely small angular sizes. . These interfering systems are capable of analyzing small details with a candle placed on the Moon.

VLA antenna system (Photo: astro.nmsu.edu)