A Very Large Telescope, and James Bond

'Don't all people think about underwater worlds on Jupiter's moons, or swimming around in the interstellar medium watching stars form, or galaxies colliding?' I asked my friend on the phone today. I was in an even nerdier mood than usual, following a morning of intense coding for my data analysis internship. The answer to my question was no, apparently, most people don't wonder about any of these things on a daily basis, or indeed ever. Following on from my nerdy mood, I found myself watching an episode of the BBC's Sky At Night from last year, a fascinating show for astronomy amateurs and enthusiasts alike. In this episode, the BBC travelled to a remote desert in Chile to look at the VLT, or Very Large Telescope, one of the world's most powerful optical observatories. It seems a certain famous fictional spy has also been a recent visitor...

In the heart of Chile's Atacama Desert, one of the driest places on Earth, sits the VLT. The landscape is almost Martian, and its stunning views and bold architecture were brought to new fame when used as a filming location for the James Bond film Quantum of Solace.

The VLT has spent 25 years staring at the sky collecting starlight in optical (human visible) and infrared wavelengths, meaning it captures light we can see as well as some that we can't. Telescopes work best in remote areas, away from artificial light pollution. Furthermore, telescopes observing infrared light need to be in dry places at high altitude, as water vapour in the atmosphere absorbs a lot of infrared light, which is why mountainous areas like this are ideal for astronomical observatories. Ground based telescopes such as the VLT make use of adaptive optics, a complicated technique that involves correcting atmospheric turbulence in images by bending tiny parts of the mirrors in real time to cancel out the wobbly distortion of light that has travelled through Earth's atmosphere. Alternatively, some infrared telescopes such as Hubble or Webb are in space, above the atmosphere and therefore don't suffer image distortion.

The Very Large Telescope. Image credit: ESO/VLT. This facility was used as a filming location in the 2008 James Bond film Quantum of Solace.

The VLT has four large telescopes each of 8.2m in diameter, and four smaller moveable ones at 1.8m wide each. They can observe the sky independently, or work together, making it the world's most advanced optical instrument. These telescopes are operated by a team of scientists from the European Southern Observatory (ESO), and sit at a height of over 2600m on the Paranal Mountain.

While the telescopes are 8.2m wide, they are only 17.5cm thick, to prevent them from being too heavy and collapsing under their own weight. Over time, the mirrors on the telescopes accumulate desert dust, affecting their image quality. Every 2 years, the mirrors are detached from their frames, cleaned, and recoated with fresh aluminium to make them shiny again. This is a delicate process, as each mirror weighs 23 tonnes and has to be shipped to another facility on the back of a truck. The whole telescope is shut down for 10 days and cleaned as quickly and carefully as possible. The mirror is first rinsed with soapy water, followed by chemicals to strip off the old aluminium layer, and once dry a new aluminium coat is sprayed on in a vacuum.

Astronomers in the telescope control room take data measurements to be used by other astronomers around the world, and help engineers look after the equipment. Over a hundred people live and work on the site, which includes a swimming pool, basketball courts and music rooms. Between observing the cosmos and playing sport, never a dull day goes by at this extraordinary observatory.

It has been instrumental in some of the greatest recent discoveries in astrophysics, and below I've included some of my favourite VLT images.

First ever image of a Sun-like star orbited by two exoplanets

This image shows a star of similar size and mass to the Sun, being orbited by two giant gaseous planets. They're called exoplanets, because they don't orbit the Sun and are therefore outside out Solar System, and instead have their own host star. It is quite incredible to think we are looking at another star-planet system in this image, similar to our own but in a much earlier stage in its evolution. This star, in the top left, is called TYC 8998-760-1, and its planets are the small bright dots near the bottom right. It is notoriously difficult to take images of planets directly, since these are incredibly dim in comparison to their bright host stars that outshine them, and this challenge can be compared to photographing a firefly next to a lighthouse from a mile away. Nevertheless, the world class engineering of the VLT has made this possible, and through blocking out some host star light using a coronagraph, its accompanying gas giant planets are visible. These are located much further away from their star than our Earth is to the Sun, in fact 160 and 320 times further respectively. For context, even Jupiter is only 5 times the Earth-Sun distance, which shows how different in scale star-planet systems can be. These planets will have formed in a disk left behind from the stellar debris that was ejected when the star was forming from a gas cloud, which can be read about in more detail in a previous article here. Learning about other planetary systems may offer insights as to how our own Solar System formed too.

A Sun-like star, TYC 8998-760-1, and its two orbiting planets. Image credit: ESO/VLT

Horsehead Nebula

For all the pony lovers out there, here is the Horsehead Nebula, situated in the beautiful Orion molecular cloud, a hotbed of stellar activity. This image shows a bright rim separating neutral, warm dust in brown from the hot, ionised gas in pink. The pink part shows where a large region of hydrogen is moving into the dusty cloud, destroying its dust and molecules, and heating up the gas, ionising it and causing it to glow in bright colours. Expanding hydrogen regions may be caused by recently formed massive stars at their centre. Another example of a similar phenomenon of hydrogen bubbles interacting with dusty gas is the famous Pillars of Creation image which I wrote about here. Dust and molecules can exist in cold parts of the interstellar medium, shielded from intense starlight by large gas layers. The dusty structures are heavily eroded by intense radiation from nearby stars, which can destroy delicate molecules, and slam the brakes on future local star formation by removing the very building blocks from which they are made. In a few thousand years, the Horsehead Nebula will have been eroded away and will cease to exist.

On the other hand, there is some debate in the astronomy community as to whether the expansion of hydrogen bubbles may also be a help rather than a hindrance to star formation, as it mixes up and injects momentum into molecular gas, and may therefore act as a trigger for kickstarting star formation. In this image alone, hundreds if not thousands of stars are shining brightly, some of which may have planetary systems in them like the photo above.

Horsehead Nebula, situated in the Orion molecular cloud complex. Image credit: ESO/VLT

Sombrero Galaxy

And finally, going in size order (because frankly as I child I was baffled by images in astronomy magazines that jumped around seemingly at random between objects of completely different sizes), here is my favourite VLT galaxy image. Like our Milky Way, this is also a spiral galaxy, which is being viewed edge-on. From my Galaxies & High Energy Astrophysics module (which I am pleased to say I scored 80% on), I remember that the oldest and most metal-poor stars are contained in the central bulge where a lack of gas prevents much future star formation, while further out in the galactic disk abundant gas allows new stars to be born. A massive black hole at the centre, as well as mysterious dark matter, keeps the stars spinning around the galaxy in circular orbits at speeds of hundreds or even thousands of km per second.

Spiral galaxy Messier 104, also called the Sombrero Galaxy. Image credit: ESO/VLT

In conclusion, this extraordinary telescope has opened the window to a whole new world of exciting astronomy, ranging from directly imaged exoplanets, to newborn stars and entire galaxies. Its successor, the even larger 39m diameter ELT (Extremely Large Telescope), will be even more powerful, and will peer yet more deeply at the sky, unravelling more secrets of the cosmos.