Our eyes are incredible organs, enabling us to interact with the world around us and to look beyond our tiny planet every time we raise our gaze up to the night sky. For centuries, it was indeed the only kind of light known to exist, and any observations of the universe were made using telescopes which could see the same radiation as our eyes, achieving better clarity of far away, faint objects in the process. However, we now know that the light our eyes can see is but a small part of the electromagnetic radiation spectrum, from the most energetic, short wavelength gamma waves to the least energetic, long wavelength radio waves.
In fact, each body in the universe gives off electromagnetic radiation of a particular wavelength, depending on its energy and temperature. Higher temperature bodies tend to give off mostly shorter wavelength radiation, while colder objects give off the longer wavelength counterpart. This means that using telescopes suitable for receiving different kinds of radiation, different objects and processes in our galaxy and beyond can be observed and more knowledge of these processes can be therefore obtained.
Gamma, X-ray, ultraviolet and infrared telescopes, however, present a problem. Our atmosphere is largely opaque to this kind of radiation, and therefore such telescopes need to be launched to space in order to be able to conduct effective astronomy. Launching such delicate instruments to space provides an engineering challenge, together with an equally challenging financial burden. Radio waves, however, are able to pass through Earth’s atmosphere largely unobstructed. In fact, the first radio waves observed from space were inadvertently captured by Karl Jansky while he was testing out some new radio telecommunication antennas.
Jansky was receiving strange signals that he could not attribute to anything other than a faulty antenna at first, until he realised that the signal was always obtained when he pointed the antenna towards a particular region in the sky, towards the centre of the Milky Way galaxy. In fact, Jansky had collected radio waves coming from the very core of our galaxy, and the strange radio source was called Sagittarius A*. This is now known to be the location of our galaxy’s central supermassive black hole, with material accelerating along the black hole’s magnetic field likely being the origin of these radio waves in a type of energy release referred to as synchrotron radiation.
Modern radio telescopes are now composed of several antennas, all working in tandem to create a synthesised aperture of a very large instrument of high resolution, called a radio interferometer. The largest breed in this kind of telescopes is currently being built in Australia and South Africa – the Square Kilometre Array (SKA). The Institute of Space Sciences and Astronomy at the University of Malta is currently working on this project, representing Malta in a joint effort with several other countries. This telescope will be several times more sensitive than any other instrument of its kind, and will be able to probe some of the earliest stages of the formation of the universe.
Josef Borg is a PhD student at the Institute of Space Sciences and Astronomy, University of Malta, and vice-president of the Astronomical Society of Malta.
Did you know?
• Using visible light, there is only so far away we can ever see. Since the universe is expanding, light waves themselves are also expanding with it. This means that the longer light travels, the more expansion on the waves themselves occurs. At some point far away from our planet, light waves would travel so much that their waves would be stretched past the wavelengths of visible light, rendering all radiation coming from that part of the universe as infrared or radio waves.
• There are likely billions of galaxies that are invisible in visible light but easily visible in radio light. Some galaxies are too far away to be seen with visible light as they are too faint and because dust between us and those galaxies blocks out most visible light. However, since they have an active galactic centre with a feeding central supermassive black hole, these galaxies are easily visible in radio images of the night sky.
• The supermassive black hole at the centre of our galaxy is approximately four million times the mass of the sun. Sagittarius A*, the strong radio source at the centre of our galaxy, is an object occupying a very small region of space with an approximated mass of around four million suns. Only a supermassive black hole fits this description; although the object has never been observed directly, observations of stars orbiting it at very close distances have given us a lot of information on this giant in our cosmic neighbourhood.
For more trivia see: www.um.edu.mt/think
Sound bites
• Rocky and habitable? ‘Super-Earth’ exoplanet may be much like our own. A possibly habitable alien world may be rocky, like Earth, and it has a neighbour, a new study reports. The potentially rocky exoplanet is K2-18b, which lies 111 light-years from Earth in the constellation Leo. It was discovered in 2015 by researchers using NASA’s prolific Kepler space telescope. These original observations revealed that K2-18b likely orbits in the habitable zone of its dim red-dwarf star – that is, within the range of distances where liquid water could exist on a world’s surface. In addition, the discovery team found that K2-18b is about 2.2 times bigger than our planet, making it a so-called ‘super-Earth’.
https://www.space.com/39010-super-earth-alien-planet-maybe-rocky.html
• Geminid meteor shower peaks on the night of December 13. The Geminid meteor shower is probably the most prolific meteor shower of the year, many times offering an even better spectacle than the more well known Perseids occurring in mid-August. This year, since the moon will be very close to its new phase, barring bad weather conditions, the observation of the Geminids should be a rather exceptional one. Looking towards the southern skies from Malta, coupled with going to a dark location, will likely provide the best chance of catching some Geminids.
To find out some more interesting science news, tune in Radju Malta on Saturday mornings at 11.05am and listen to Radio Mocha.