Happy 25th Birthday Hubble Space Telescope!

On this day 25 years ago the Space Shuttle Discovery was launched from the Kennedy Space Centre on Cape Canaveral in Florida. After launch the Space Shuttle rose to an altitude of 380 miles and began to orbit the Earth. In the days that followed the crew of the Space Shuttle opened the shuttle's cargo bay doors and deployed its valuable payload, the Hubble Space Telescope.

The launch of Space Shuttle Discovery, with the
Hubble Space Telescope on board (Credit: Wikipedia)

That was 25 years ago, and ever since then the Hubble Space Telescope has acted as the world's premier astronomical observatory. In that time Hubble has made an immeasurable contribution to our understanding of the cosmos, from measuring the speed of the expansion of the Universe, finding the first evidence for dark energy, and discovering planetary systems forming in the Orion Nebula.

The Hubble Space Telescope is not the only astronomical observatory in space, in fact there are dozens of them. It wasn't the first such observatory and it certainly won't be the last, but it is probably the most important, not just for the scientific discoveries it has made, but also for how it has brought those discoveries, as well as thousands of beautiful images of the cosmos, to the public. In this article I want to share some of those images, and the science behind them, with you all.

The Pillars of Creation in the Eagle Nebula, imaged by the
Hubble Space Telescope in 1995
(Credit: Hubble Space Telescope)

Perhaps one of the most famous images taken by the Hubble Space Telescope, and one of the first to lodge itself firmly in so many people's hearts, is the magnificent image of forming stars in the Eagle Nebula. The image, which was quickly dubbed the Pillars of Creation because of the stars being created within the nebula, showed for the first time the amazing detail in star forming regions such as this. The pillars themselves, sometimes referred to as elephant trunks, are giant clouds of gas and dust that are being slowly eroded by a cluster of massive stars just above this image. Those stars are sculpting and eroding this cloud of gas and dust, and potentially, as was later shown, halting the star formation process within them. The Hubble Space Telescope revisited this image as part of the 25th Anniversary celebrations this year, producing a new, larger and higher-resolution image of this amazing nebula.

The merging Antennae Galaxies, imaged by the
Hubble Space Telescope in 2006
(Credit: Hubble Space Telescope)

The Hubble Space Telescope didn't just spend its time imaging star forming regions like this, it also produced a huge number of very detailed images of distant galaxies. One of my favourite images of these galaxies is that of the Antennae Galaxies that has been imaged by Hubble multiple times, most recently in 2006. The Antennae are actually two galaxies that are in the process of merging as they interact, and this interaction has quite radically torn these galaxies apart, as the image shows. This apparent destruction has, rather paradoxically, led to a very brief but intense period of star formation that astronomers refer to as a starburst. The Hubble Space Telescope images are so detailed that they have allowed astronomers to study the star formation in these distant galaxies and even resolve individual star clusters within them. Getting such a detailed view of this important phase of galaxy evolution has been really useful for astronomers to understand how galaxies merge.

The Hubble Deep Field, imaged by the
Hubble Space Telescope in 1995
(Credit: Hubble Space Telescope)

Perhaps one of the most unique images taken by the Hubble Space Telescope is that of the Hubble Deep Field, which was imaged in 1995 from 6 days of exposure of an apparently empty patch of sky. This tiny area, one 24-millionth of the entire sky, was chosen because it was almost completely devoid of any stars and galaxies. The questions astronomers were effectively asking by taking this image was, what will we find in the darkest and emptiest areas of space?

The answer was that this apparently empty area of space was actually full of galaxies! Almost all of the 3000 objects in this image are distant galaxies, billions of miles away. Some of the galaxies are so distant that it has taken almost the entire age of the Universe for their light to reach us, allowing us to see what they looked like when the Universe was very young. Images like this have been vital for helping astronomers understand both the large-scale structure of our Universe as well as how galaxies have changed over the lifetime of the Universe.

Finally I want to end with a new image taken by the Hubble Space Telescope very recently. This image was released to the public yesterday to celebrate the 25th Anniversary of the launch of the Hubble Space Telescope, and you can see this amazing image below.

The Hubble Space Telescope's 25th Anniversary special image release showing the massive star cluster
Westerlund 2 and surrounding nebulosity (Credit: Hubble Space Telescope)

The image shows the massive star cluster Westerlund 2, one of the most massive clusters of young stars in our Galaxy (and one which I have studied in the past and talked about before on this blog). This image is so large and detailed that not only can you make out many hundreds of young and massive stars in this cluster, but you can also see the beautiful nebula that surrounds the cluster and make out young stars forming within it! This is an amazingly detailed image, which I encourage you all to have a look at in more detail here.

You can see more images like these on the Hubble Space Telescope's gallery webpage, or follow the various events celebrating this anniversary on the Hubble Space Telescope's 25 Years webpage. Over the next few months I'll talk more about some of the amazing discoveries from the Hubble Space Telescope, the history of how this great observatory came to be, and the exciting telescope being built to replace Hubble in the next few years.

Searching for stars that run away

So it's observing proposal season and Wednesday was the ESO deadline, which means panicked proposal writing and last-minute scribbling all round.

ESO is the European Southern Observatory, Europe's premier observatory in the southern hemisphere, which operates some of the largest and most advanced telescopes in the world. This includes the four behemoths that make up the VLT, the Very Large Telescope (except there's four of them), each housing a 8.2m mirror and some of the best astronomical instruments in the world.

ESO's Very Large Telescope(s) in Chile (Credit: Wikimedia Commons)

One of the proposals we submitted is part of work by my colleague Mike Mohr-Smith to improve the census of massive stars in our galaxy and identify where they formed. Massive stars are very rare and live very short lives (on astronomical timescales at least), but affect the evolution of other stars and the galaxy as a whole in very important ways. How massive stars form is a major unanswered question in astronomy, and since they live such short lives finding these stars and tracing them back to their birth-sites is an important avenue of research.

So we've recently identified a number of hitherto-undiscovered massive stars in the vicinity of one of the young massive star clusters in our galaxy, Westerlund 2. The most massive stars we know of are nearly always found deep within star clusters, and some people have suggested that they can only form in such environments, so finding massive stars near a massive star cluster, but not within it, is very interesting.

The massive star cluster Westerlund 2 (Credit: Robert Gendler)

So the question arises, did these stars form outside of the cluster (which would make them very special) or did they form in the cluster but have since been ejected? The first step in answering this question is to measure the speed these stars are moving relative to the cluster. If the stars have been ejected (known as runaway stars) they should be moving very fast away from the cluster, but if they formed in isolation their velocities will be much lower.

By taking high resolution spectroscopy of these stars we can measure their speeds by observing the shifts in the positions of known spectral lines due to the Doppler effect. This is the same effect that causes the pitch of a siren to change as a vehicle moves towards you and then away from you, but instead of affecting sound waves it is shifting light waves.

Representation of the Doppler-shift effect on spectral lines
(Credit: University of Virginia)

This image shows a spectrum of light, which is light split into its constituent parts using a prism. What was originally white light has now been split into all the colours of the rainbow (it's actually the same effect that causes a rainbow!).

On top of the rainbow you can see dark lines, which are known as spectral lines. These are caused by atoms of different elements absorbing light at certain wavelengths (in certain parts of the spectrum). When an object is moving away from us, it's light is redshifted, meaning spectral lines shift towards the red part of the spectrum, while when an object is moving towards us it's light is blueshifted, meaning spectral lines shift towards the blue part of the spectrum. The faster an object is moving relative to us, the greater the shift in the position of the spectral lines. So by observing the spectrum of light from a star, measuring the positions of it's spectral lines and comparing them to the positions we know they should be at we can determine how fast the star is moving towards or away from us.

So our objective is to use one of the instruments on the VLT to acquire high-resolution spectroscopy, measure the positions of the spectral lines and therefore the speed the stars are moving relative to the stars in the cluster. With this information we can answer the question of whether these very massive stars formed inside the cluster or outside of the cluster.

That's our plan at least, and that's what we've written to the friendly people at ESO asking them if we can use their telescope to do this project. I'll let you know what they say!