Australia’s Role Helping the Giants

Around Christmas time in 1995 - a recently orbited space telescope photographed a seemingly empty patch of sky near Ursa Major for around 10 days. It would take 342 exposures over this period, with the region selected to be as empty of Milky Way stars as possible. 

The result - the first of the Hubble Deep Field images (HDF-N) - would change the course of our understanding of the universe. Beyond the extent of our spiral island of stars, were 3,000 new, young galaxies in this tiny square of the sky - some of them, so distant in the past they had not had time to form all of their stars. 

To be sure that this patch of sky wasn’t special, Hubble repeated the process in 1996 (HDF-S) and found another sprinkling of galaxies in the Universe. Everywhere we looked, there were billions of other galaxies out there. 

These images created a huge shift in our understanding of cosmology, the evolution of galaxies and our perspective of our place in the grand scheme of things. This was no easy feat, and was obtained by Hubble’s advantage of existing above Earth’s atmospheric distortions - that is, a 2.4 metre diameter telescope, orbiting 540 km above Earth.

So what if we could go bigger?

Whilst the Hubble telescope and its follower - the James Webb Space Telescope, have and will revolutionise our perspective of the universe, through their main advantage of being above Earth’s atmosphere - the reality of building bigger telescopes in space equates with higher costs and risks. 

So scientists are turning to a new class of instruments - ground-based telescopes with giant eyes that can look further and deeper than Hubble, even from the surface of Earth. These behemoth telescopes are the future of visual astronomy (in a number of bands across the electromagnetic spectrum) with the ability to not only capture and catalogue the deep sky in detail, but survey the entire sky within days. 

The advantages of these telescopes being constructed on the surface (as opposed being orbited) is the opportunity to go bigger - lifting huge swaths of mirrors into space presents enormous risks and costs, let alone maintenance capabilities. As such, the collecting power of mirrors - the eye of the telescope - can become larger and more powerful here on Earth.

One disadvantage ground-based telescopes have, is atmospheric distortion - that is the turbulence of the different layers of atmosphere the telescope must resolve through to obtain an image of the object in space. Though, scientists and engineers have come up with some clever ways to get around this.

Firstly, most large telescopes of this nature are built or being built away from populated areas - and usually, high on mountains, well above the thicker parts of Earth’s atmosphere. Being higher in the atmosphere also means less moisture - an ideal solution for any optical telescope (clouds tend to be a bit of a problem). 

To go one better, techniques like advanced optics are applied - where a laser is used to measure these distortions in the air and change the shape of the collecting mirrors to account for the turbulence - which result in some of the sharpest images taken. 

One thing that will always play on the minds of organisations who fund these projects are the risk value, insurance costs (and protections), as well as the ongoing considerations to maintenance - after all, the thing has to last for a number of years to derive its true value.

Orbiting telescopes fall short in this area - the risks (which equate to costs) are high from launch, through to in-situ orbital challenges (like space debris); the insurance costs are enormous - often a derivative of the cost of production which soars into the billions and lastly, if the thing breaks in space - it’s not like it’s an easy trip to go and fix it.  

So the next best thing is going bigger on the ground.

In this new age of large telescopes, a number of new observatories are being built around the world to compliment these requirements. These include:

• ESO Extremely Large Telescope (E-ELT) - Once completed, it will also reside high in the Atacama Desert of Chile, boasting a 39.3 metre diameter, made up of 798 smaller hexagonal segments. 

• Thirty Metre Telescope (TMT) - The only of the extremely large telescopes to be built in the northern hemisphere (controversially on Mauna Kea in Hawaii), the TMT will host a 30 metre primary mirror made of 792 smaller hexagonal segments.

And one that Australian scientists are involved in - the Giant Magellan Telescope (GMT).

Coming in at a price tag of about USD$1 billion, the Giant Magellan Telescope (GMT) is an extremely large optical and infrared telescope that will look deeper into the heavens and explore back in time to an epoch, shortly after the big bang.

The science case behind the GMT has developed over the course and evolution of the project, but has its origins in the 2010 Decadal Survey Report “New Worlds, New Horizons in Astronomy and Astrophysics”. 

Outlined in the 2018 Science Book, the case for the GMT covers the upcoming transformative impact that large aperture ground-based telescopes will have across a range of areas spanning observational astrophysics, such as the discovery of exoplanets around nearby stars (including imaging and studying their atmospheres), the formation of the first and most distant stars, and conducting a wider survey of galaxies and black hole candidates to name but a few areas the GMT will explore. 

The GMT will also host a suite of instruments, which includes:

• G-CLEF (Visible Echelle Spectrograph) - a high resolution (25,000 - 120,000) spectrograph operating between 350 nm - 950 nm used to study radial velocities, stellar astrophysics and the intergalactic medium (IGM)

• GMACS (Visible Multi-Object Spectrograph) - developed to study very faint objects, galaxy evolution and evolution of the IGM

• GMTIFS (Near-Infrared IFU and Adaptive Optics Imager) - with a spectral resolution ranging between 5,000 - 10,000, this instrument will study near-infrared between 0.9 - 2.5 microns

• GMTNIRS (Infrared Echelle Spectrograph) - a high resolution (50,000 - 100,000) infrared, 1.5 micron narrowfield spectrograph aimed at studying exoplanets and early stage planetary systems and debris discs

• MANIFEST (Facility Fibre Optics Positioner) - a robotic (starbugs) positioning system, that compliments G-CLEF and GMAC S

• ComCam (Commissioning Camera) - camera used for ground layer adaptive optics, initial telescope alignment and verification of natural seeing

Looking deeper into the cosmos from ground requires the largest optics, far bigger than the one we can send into space. GMT will combine seven 8.4 meters circular mirrors of 18 tonnes to make a primary mirror having a collecting area of around 25 meters. The process of developing the mirrors itself is a massive task, complimenting the size of the structures. Once the thermally, chemically and mechanically stable borosilicate glass is poured inside the kiln, it’s closed and rotated whilst being heated to 1,170-degrees Celsius. It then takes six months for the mirror to cool down enough before polishing can occur.

The telescope is being built on the Las Campanas Observatory in the Atacama Desert, Chile by an international consortium of twelve Founder institutions from the USA, Australia, Brazil, South Korea, and Chile as the host country. This monstrous ground-based telescope will be capable of producing images 10 times sharper than those from the Hubble Space Telescope and 3 times sharper than from the upcoming James Webb Space Telescope, which will reside in orbit. 

This will open a new era of science and expand our understanding of the universe. Extremely large telescopes are the future of optical and infrared astronomy and Australian access to an extremely large telescope is essential to our local astronomy community for continuing to contribute to astronomy at the international level.

The power to see deeper into distance with telescopes come from their ability to gather more light than our eyes - through a larger aperture. This translates to a larger light collecting area, in addition to potentially higher angular resolution. 

By increasing the size of the ‘eye’ (in this case, the telescope’s primary mirror which collects incoming photons), telescopes basically see and can focus more information than smaller aperture objects like the eye. Of course there are a number of other factors that impact this, including focal length, focus ability, atmospheric seeing, filters, light levels and more - but generally, the bigger the eye the more collecting power it is going to have. 

The GMT will use some of the world’s largest mirrors once they’ve finally been cast - each is a massive 8.417 metres in diameter. The arrangement of the mirrors of the GMT take on a sunflower like shape, with once central mirror surrounded by six in a symmetrically tilted angle. All seven mirrors will act as a single mirror, providing the telescope with a resolving power like that of a telescope with 24.5 metres diameter. 

To work properly in unison, each of these mirrors must have the exact same curvature (similar to that of a potato chip) - polished to a precise optical prescription that remains within the desired shape by no more than 1/20 of a wavelength of green light - or approximately 25 nanometres.

Australia is a 10% partner in the massive new GMT project. This contribution will give Australia a 10% share of the telescope, guaranteed observing time, and allow Australian industry and scientists to play a significant role and remain at the forefront. 

The investment will enable Australian scientists to unveil the mysteries of the universe and give an opportunity to the industry to build high technology equipment for the telescope. Future telescopes like GMT demand a new class of astronomical instruments.

Furthermore, Australia is playing a key role in the GMT project by building two instruments and some crucial components of the adaptive optics systems, which will help achieve a resolution sharper than the Hubble Space Telescope.

One of the instruments to be built for GMT by the Australians is the Many Instrument Fibre System coined MANIFEST by the Australian Astronomical Optics. For a billion-dollar telescope with an unusually large field of view, MANIFEST will build a capability to rather than observe one object at a time, observe hundreds. 

MANIFEST is a fibre positioner consisting of hundreds of walking robots called Starbugs which can within minutes move from one position to the other on a glass plate looking to the sky. This is a similar technology that is used for the Taipan instrument at the UK Schmidt telescope, in NSW.

MANIFEST is designed to enhance the functionality of the telescope by feeding these robotic fibres to all the spectrographs of the GMT to enable observations of hundreds of targets in one go. 

MANIFEST will also be able to connect to any spectrograph (optical or infrared) at the telescope and turn it from one object to a multiple object spectrograph through its fast and accurately positioned fibres. Such an elegant and high technology equipment that is fast, efficient, and capable to deal with multiple interfaces has never been designed, and showcases the proficiency and skill of our Australian scientists and engineers.

A second Australian instrument will operate with the GMT, this one developed by researchers and engineers at the Australian National University (ANU). The name of this instrument is the GMT Integral-Field Spectrograph (GMTIFS).

This near-infrared imaging and integral-field spectrograph will be able to take in light covering large areas of the sky, producing a detailed image - in addition to the ability to obtain spectra of objects across the entire field of view.

Earth’s atmosphere (or any body for that matter) can be considered a fluid. That is, it is very dynamic with a range of different pressures, temperatures, wind speed and direction, humidity, volume of particles like dust, different elements (like ozone vs. nitrogen) and comes in different layers. 

Photons arriving from beyond the atmosphere (light from stars, planets, moons, comets, galaxies, the Universe in general) need to pass through all these dynamic obstacles before arriving at the aperture of any telescope. Much like refraction causes the wobbling of small items at the bottom of a pool when we observe it from outside, point-like objects (like many stars) thus become distorted as their photons are jolted around as they pass through Earth’s dynamic atmosphere. 

To combat this, in the early 1990s - a new technology called adaptive optics was introduced (in line with the rise of computers). The technique is built upon the premise of using measurements of atmospheric distortion to situationally adapt, and thus counter this distortion, allowing imaging and observations of incoming photons from astrophysical objects to become sharp again. 

Adaptive optics systems with sophisticated deformable mirrors in telescopes can remove real-time distortion (i.e. twinkling of stars) in the images caused by the turbulence of the earth’s atmosphere. This is achieved in a number of ways - at first, the incoming astrophysical light is measured on a wavefront sensor for a few milliseconds. Then a computer calculates the optimal mirror shape to correct for distortions and the shape and surface of a deformable mirror is altered to account for distortions, thereby removing their impact. 

The atmosphere however is not homogenous, and what might be turbulent in one section of the sky, is likely not going to be in another. As such, adaptive optics utilises local measurements (i.e. as close to the observed target) to consider as part of its calculation.

To do this, a bright nearby guide star is used to measure the local atmosphere near the target. This gives a good local indication of the turbulence of the atmosphere and the computer can calculate from there. 

Often, a nearby bright guide star might not be available - so scientists fire laser beams into the higher layers of the atmosphere to create an artificial guide star which the computer can then use to calculate turbulence in the region, before changing the shape of the deformable mirror.

When the great eye of the GMT finally opens once construction has been completed, and the first light from distant suns rain down on its enormous mirrors, our understanding of science will change, and rather rapidly. As with all of the next-generation, larger telescopes being developed - leaps and bounds will be made through massive volumes of data, of which will become available to the public as well. 

Direct imaging of local exoplanets - currently hiding within the glare of their host stars, and only detected through indirect methods will become a reality. Capturing light curves from these worlds in other systems will allow analysis of their atmospheric composition - giving us insight into what processes are occurring at these far away locations. 

Looking far back in time, to the dawn of the age of galaxy formation will highlight how these structures came to be - thus revealing more information about elusive dark matter, and hopefully shedding some more light about dark energy. 

Working with a global network of connected observatories across the electromagnetic and gravitational-wave spectrum, the GMT will be able to hone in on transient events - potentially revealing the source of mysterious fast radio bursts, or catching an unfortunate stellar companion being shredded by an ever-so-hungry black hole.

Like the Hubble Deep Field images changed our view of a seemingly empty patch of the sky forever, this new generation of telescopes will re-write the context of textbooks - answering some of our most fundamental questions, and raising a new batch to keep us on our toes, always asking about the who, the what, the how and the why. 

It’s a fantastic time for Australia to be deeply involved at the very forefront of astronomical research and science. 

Official images sourced from the Giant Magellan Telescope website.