In the previous article we explain how radio astronomy came about. In this we will see what it is and how it works.
The physical mechanisms that are at the base of radio emissions by celestial objects are different from those that make them shine with visible light. While almost all electromagnetic waves within the visible spectrum have a thermal origin (that is, they are a consequence of the high temperature at which the matter of celestial objects such as stars is found), electromagnetic waves within the radio spectrum are due, especially, to the movement of elementary particles charged with energy.
One of the typical mechanisms of celestial radio-wave emission is, for example, the so-called Synchroton radiation: the spiral movement of electron beams that travel at the speed of light through stellar magnetic fields or Galactic
Not all celestial bodies that are powerful emitters of visible waves are also electromagnetic waves. For example, the Sun and the stars, which we see easily with the naked eye, are very weak sources of electromagnetic radiation. If our eyes were sensitive to radio waves instead of visible light, the sky would change its appearance. The Sun would become a weak source, the Moon and the planets would be almost invisible, almost all the stars would disappear from the scene and the sky would be dominated by an intense strip, the Milky Way (corresponding to the equatorial plane of our Galaxy). Here particle flows cosmic ray components produce synchroton radiation.
In addition to this excessive strip that would occupy the entire celestial vault, we would also see isolated sources inside our Galaxy, corresponding to Supernovas, Pulsar, Nebulae. We could even see very distant objects that are beyond our Galaxy, such as external galaxies of the Andromeda type, and also the Quasar, that is to say the mysterious nuclei of galaxies that seem to be found in the confines of the Universe.
Radio astronomy has significantly increased the knowledge of the Universe at all levels. On the planetary scale, for example, certain mechanisms of interaction between local magnetic fields particles have been known thanks to radio observations, as in the case of Jupiter, which emits synchrotron radiation precisely by virtue of the powerful magnetic field that surrounds it.
From the Sun it was possible to study some phenomena such as spots and eruptions, which are the headquarters of radio broadcasts. Even annual meteor showers have become an object of radio astronomical research, thanks to the traces of the particles that burn in the atmosphere ionize the atoms, therefore, they can be captured with radio techniques, even in broad daylight.
On a broader scale it has been discovered that our Galaxy is not only composed of a set of stars, but there are also, among them, large quantities of cold hydrogen and invisible to observation with optical instruments. The distribution of this gas, and the fact that it gives our Galaxy the characteristic spiral-shaped disk configuration, are a result of the investigation of the cycle by means of radio waves. The cold hydrogen is visible in the radio wave domain, because it has a characteristic emission in the wavelength of 21 cm, which is due to spontaneous reversals of rotation of its electrons as a result of energy absorption.
One of the achievements of radio astronomy is the individualization of numerous species of interstellar molecules. On an extragalactic scale, radio astronomy has made important confirmations of the cosmological theory of the expanding Universe after an initial Big Bang, thanks to the discovery of distant radio sources that show a strong Redshift and thanks to the discovery of Background Radiation.
Radio sources are also cataloged with criteria similar to those of stellar catalogs. Originally they used to indicate the sources that were within the same constellation with an alphabet letter from A, respecting the order of magnitude. For example, the most powerful radio source in the constellation of Taurus, the famous Crab nebula, was named Taurus A. However, the number of radio sources has increased so much in recent years that this simple cataloging has proved insufficient.
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