Science Sunday: The Square Kilometre Array (Part 2)
Part one can be read here.
Welcome to part two on the Square Kilometre Array, where I talk about the final three key science projects of the SKA.
It is well-known that the earth has a magnetic field, and we also know that stars, planets and galaxies also posess them too. These magnetic fields are attributed to the motion of electrically charged clouds of gas, and they play a huge role in the origin and evolution of celestial forms. Unfortunately, because they are not visible and only able to be detected by indirect means, they are very poorly understood. Once such means of indirect detection is synchrotron emission, and this is often used to detect if an object is magnetic, and if so, how strong and in what direction its field is pointing.
However, many objects can't be detected using this method because the particles aren't energetic enough, so we must rely on an effect called "Faraday rotation". Polarised light is light that has waves all oriented in one direction. If polarised light passes through an object with significant magnetisation, the direction of polarisation, the angle at which the vibrating light waves are inclined changes slightly, and this change is readily detectable by the radio telescopes. This is a much easier way of deducing important information about the strength and direction of magnetic fields.
There is one pitfall of this method however– it relies on a bright background object lying in line with the galaxy or gas cloud we wish to study the magnetism of, and this is not exactly a likely occurrence. This is where the increased range and sensitivity of the SKA comes in, giving unique new insight into the ways the universe's magnetism has shaped the evolution of stars and galaxies, and potentially where it all came from.
The SKA will help in the search for life in our universe in multiple ways. The SKA is more sensitive and can detect a wider range of signals– both in frequency and in the volume of the galaxy. This increased sensitivity will be able to detect signals comparable in strength to television transmitters, thus scientists will potentially be able to search for "leakage" signals from technologically advanced extraterrestrial civilizations.But the likelihood of finding intelligent life in our universe is considerably lower than our chances of finding other forms of life. You'll be aware that a lot of the search for life has been focused on earth-like planets. The problem with the search for earth-like planets so far is that not that many of them are really earth-like, and if they are, they aren't orbiting around sun-like stars (and the planets that are orbiting around sun-like stars are mostly Jupiter-like). Another problem is that the habitable zone of a star is much too small to be visible with most telescopes, but the widely separated antenna on the SKA will change this. It is also hoped that the SKA will help us out with the questions of why gas-like planets are more common around stars like our sun by studying the process of planet-building. Studies of young stars has shown that they are surrounded by disks of dust that form planets. This dust has much more surface area than the planets it forms, and tis surface area intercepts light energy from the star which can in turn be converted to heat ("termal dust emission")– which is detected at short radio lengths. Perfect for the SKA! By conducting large-scale surveys, we will be able to see planets in various stages of formation, learn about the mehanisms of planet formation and answer questions about why gas planets rather than those like our own seem to be more common in solar systems with stars similar to our sun.
The cosmic microwave background radiation has given us great insight into what the universe looked like 300,000 years after the Big Bang, when no galaxies, stars or planets existed, and different types of telescopes (optical, radio, x-ray) have allowed astronomers to observe galaxies as long ago as when the universe was a billion years old. However, the time inbetween this has been notoriously difficult to study– and this is an interesting phase in the evolution of the universe when the first protogalaxies and quasars were froming. The Wilkinson Microwave Anistropy Probe and the Sloan Digital Sky Survey have given us some clues about these– including different mechanisms of formation of galaxies, and super-massive stars.
The SKA is important to the study of objects in this epoch because when the structures of these objects started to form the gas was electrically neutral and smoothly distributed, making radiation hard to detect. Fortunately, neutral hydrogen produces weak radiation at the 21cm emission spectrum line which is detectable by the SKA. As these objects grow and produce light, they ionise pockets of gas, this emission line is shut off, or "re-ionised".
By observing these changes in ionisation, much can be learnt about how objects formed in the early universe.
So now you know a little but about the SKA, and why it is important (and exciting!). As I noted in part one, most ground-breaking discoveries in astronomy have been accidental, and the SKA is sure to expand our understanding of the universe in as-yet-unknown ways.
Be sure to click the links for more information, and let me know if you think I might have got anything wrong or you have any questions!
Featured Image Credit: Google Images