Things are taking off at Mount Stromlo ... 2
The next generation Giant Magellan Telescope (GMT) will be recording spectacular images of the cosmos but straight imaging of the universe will only be a small part of its mission. The vast majority of its time will be spent directing the light collected into an array of specially designed instruments that will analyse their light. One of these, the GMT Integral-Field Spectrograph (GMTIFS), is being designed by researchers at the Mount Stromlo Observatory.
Spectroscopy (splitting light into its component colours or frequencies) has been of fundamental importance to astronomy for more than a century. It enables astronomers to determine the chemical composition of stars and nebulae by studying the sharp emission and absorption lines present in starlight. Because relative motion between the light source and observer causes a shift in the frequency or wavelength of these lines (Doppler shift) – similar to the way the pitch of a moving siren can be heard to change – they can also be used to measure the velocities of stars and rotation of galaxies.
In its simplest form a spectrograph places a slit at the focal plane of the telescope and disperses the light using either a prism or more commonly a diffraction grating. The problem with this design is that if you’re interested in something extended like a galaxy, it only enables you to measure the spectrum of one section through it.
An Integral-Field Spectrograph (IFS) takes the concept of spectroscopy further as it enables astronomers to record the spectrum of each point in the galaxy simultaneously. This makes it a much more useful and powerful instrument.
Professor Peter McGregor is leading the design team for the GMTIFS.
“What we’re aiming to do is build a dedicated instrument that will take full advantage of the incredible light grasp and resolution of the GMT,” he explains.
One of the key things with the GMTIFS is that it will sit after the adaptive optics module that corrects for the constant distortions created by the Earth’s atmosphere. This means that it will be able to take full advantage of the GMT’s enormous spatial resolution when generating its spectroscopic maps of objects.
“With adaptive optics and IFS working together, we’ll be able to do science that simply can’t be done with current generation telescopes,” says Professor McGregor.
“Using the GMTIFS we should be able to not only see the structure of early galaxies, but also measure the motions of the different parts of them and get a much better idea of how they evolve.”
Closer to home, the GMTIFS will enable astronomers to see nearby galaxies in such detail that the motions of individual stars can be mapped. This will enable them to study how the giant black holes that lie at the core of most galaxies influence the motion of the stars that lie within their spheres of influence.
“Our current thinking is that the presence of super massive black holes at the centre of most galaxies, including our own Milky Way, has a profound influence on the way the galaxy evolves and behaves,” says Professor McGregor. “So having access to this kind of data will really help us to understand this process.”
The GMT and its Integral Field Spectrograph should also enable astronomers to make great advances in the study of the formation and nature of planets orbiting other stars.
“Using the GMT we should be able to not only directly image nearby planetary systems, but to do spectroscopy on individual planets in such systems,” explains Professor McGregor. “And that could be the critical step in detecting life outside the solar system.”
However in spite of his enthusiasm for the GMT and its instruments, Professor McGregor isn’t expecting a lot of personal benefit from the project. “Realistically first light will be around 2020,” He says, “And by then I’ll have more or less retired. But what this instrument and Australia’s partnership in it really mean is that the next generation of Australian astronomers, kids that are in high school and college now, will have a wealth of opportunities at their disposal. This is a really great time for young scientists in Australia to get involved in astronomy.”