Science Sunday: The Square Kilometre Array (Part One)
The Square Kilometre Array (SKA) is a large radio telescope currently in development. It will be the world's largest and most sensitive radio telescope, and (as the name suggests) it will have a total collecting area of approximately one km. Radio telescopes are used by astronomers to detect low frequency radio waves that pentrate earth's atmosphere. They are of intereste because they offer an alternative view of the universe to what is seen with optical (visible light frequency) telescopes, and also reveal areas that are obscured by cosmic dust.
The location of the SKA is still to be decided, however it is known that it will be in the Southern Hemisphere as this offers the best view of our own galaxy, the Milky Way, and where radio interference is least. There are two bids for the site of the SKA, and the final decision will be made this year. The two short-listed sites are in South Africa and a joint bid by Australia and New Zealand. I'll admit as a Kiwi astro-interested physics student looking at employment in the future that I have Very Strong Feelings about where I'd like it to be located, however, no matter where it is, there will still be 20 countries from all over the world involved in the research, and the discoveries are sure to be interesting!
The really exciting thing about the SKA is, of course, the science. There are five main projects, and two of these are outlined below (Come back next Sunday for the final three!). However, as many of the most profound discoveries made in Astronomy have been total accidents, the SKA is going to have a flexible design to enable exploration of the unknown.
Recently the Nobel Prize in Physics was awarded to a group that discovered that the universe was actually accelerating in its expansion, rather than slowing down under the gravitational attraction between galaxies. The reason for this is still a mystery, however it is thought that either some other component, dubbed 'dark energy' is present which cancels out (and then some) the gravitational attraction. Alternatively, we have an incomplete understanding of gravity as descibed by Einstein's General Theory of Relativity. In order to find out more about Dark Energy and Galaxy Evolution, scientists are using the increased sensitivity of the SKA to conduct a large survey of galaxies, by searching for their characteristic 21cm hydrogen emission line. As the hydrogen gas is travelling at different velocities within a galaxy, and because of the doppler effect, this gas will be detected at slightly different frequencies. From this, astronomers can infer how fast a galaxy is rotating, and thus other important information such as the total mass it must have in order to not fly apart. If the gas is rotating faster, than the mass of the stars in the galaxy would allow for, then this gives evidence for the existence of dark matter that produces gravitational attraction for the galaxy to stay together, but does not produce light.
All of this is hoped to allow for measurement of effects hypothetically caused by the presence of dark energy which are causing the accelerating expansion of the Universe.
Einstein's Theory usurped Newton's classical mechanical theories, and the SKA will be conducting tests to challenge this theory so we can ultimately understand the universe in much more detail, and discover if alternative theories need to be constructed to more accurately descibe space, time, and gravity. In order to test General Relativity, we need to find a pulsar– a rotating neutron star that is pulsating regularly in precise intervals– orbiting something incredibly massive, such as a black hole. These are incredibly rare, however it is thought that there might be some in the disc of our own galaxy and the sensitivity of the SKA will allow detection of them. General Relativity makes predictions of the nature of black holes, and by researching the regularity of the pulses of pulsars, we can test General Relativity and the nature of black holes.
Pulsars were also used to confirm the presence of gravitational waves (ripples in space time) due to the motion of stellar-sized objects. It is also expected that the Big Bang and collisions of super-massive black holes will have created gravitational waves, and the SKA will be used to find them at wavelengths that are not able to be detected by current technology.
With the SKA, astronomers can challenge our current understanding of gravity and relativity, and potentially make exciting new discoveries about the nature of these phenomena.
Anything I've missed? Anything I've got wrong? Feel free to comment!
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