Stunning “first-light” astronomical images have just been produced by UK-led SPIRE instrument on board the Herschel Space Observatory.
On June 24 2009, the SPIRE instrument was able to observe the sky for the first time since its launch in May.
The telescope was trained on two galaxies called M66 and M74 to get a first impression of exactly what the instrument could see. These images were really just a quick “open the lens cap and take a shot”, without any real effort to optimise the camera or processing software. The results were better than anyone expected!
Professor Matt Griffin of Cardiff University, and SPIRE Principal Investigator, said: “These quick first light observations have produced dramatic results when we consider that they were made on day one. Astronomers planning to use SPIRE are delighted because they can see straight away that the main scientific studies planned with the instrument are going to work extremely well. In fact all three instruments on Herschel have now shown what they can do, and the results are spectacular all round.”
The SPIRE camera responds to light at wavelengths between 250 and 500 microns (500-1000 times longer than the wavelength of visible light). It is designed to look for long-wavelength light emitted from clouds of dust in regions where stars are forming in our own and other galaxies. Observations at these longer wavelengths do not produce the “pretty pictures” obtained at shorter wavelengths, such as the visible light detected by the famous Hubble telescope. What they can do, however, is see features in celestial objects that are invisible to Hubble; and with Herschel’s giant 3.5m mirror, the detail becomes extremely rich.
The target galaxies showed up prominently, providing by far the best images yet seen at these wavelengths. Many other, more distant, galaxies were also seen in the field of view.
The images effectively show reservoirs of gas and dust that are ready to be turned into stars in the galaxies. In M66, a spiral galaxy located about 36 million light years away the images show most of the dust is located in the centre of the galaxy, which is why these areas appear brighter.
In M74 a face-on spiral galaxy located about 24 million light years from Earth, SPIRE was able to trace the cold dust between the stars, and the spiral arms of the galaxy appear much more enhanced. They also contain many faint dots that are actually distant galaxies in the background.
Professor Steve Eales, Cardiff University, who will be working on the data from Herschel, said: “The big spiral galaxies are very beautiful but I was blown away by the hundreds of distant faint galaxies around M74. Now we’ve got to figure out what they tell us about the evolution of galaxies.”
These images illustrate the power of Herschel for studying galaxies. The most obvious feature of the images is the bright spiral galaxies in their centres. This is the first time anyone has seen what galaxies look like at these wavelengths, and although these pictures may look like optical photographs of spirals, the big difference is in what is producing the radiation: in an optical photograph it is stars; in these images it’s dust, the tiny solid grains of matter between the stars. Dust grains may not sound terribly exciting, but they are the key to how stars form, and they also act like smoke, hiding half a galaxy’s optical light from traditional telescopes like Hubble. These images, the first of thousands of images that Herschel will obtain of nearby galaxies, therefore hold huge clues about the metabolic processes within galaxies.
Equally important, however, is something that is not quite as obvious to the eye. The image of M74, in particular, is surrounded by hundreds of ‘blobs’. Each of these blobs is a distant galaxy. Because of the finite speed of light, distance equates to time, and a galaxy at a distance of one billion light years is being seen as it was one billion years in the past. Therefore, these galaxies are not only a long way away, they are a long time ago. By studying the properties of the hundreds of thousands of distant galaxies that will be detected by Herschel, of which these are a foretaste, we will be able to take a major step forward in our understanding of how galaxies were formed and how they have changed over time.
Prof Steve Eales, Cardiff University
The images have given astronomers an exciting foretaste of the important scientific studies planned with SPIRE: the instrument will look at star formation close up in our own galaxy and in nearby galaxies, and it will search for star-forming galaxies in the very distant universe. Because these galaxies are so far away, their light has taken a very long time to reach us, so by detecting them the scientists will be looking into the past and learning how and when galaxies like the Milky Way were formed.
“These thrilling images confirm that the mission should give us answers to some of the great mysteries surrounding the evolution of our Universe. We shall be able to watch as galaxies shed their dusty cocoons and develop from the staggeringly distant, small innocuous blobs you can see in the background of these images – actually colossally powerful starbursts dating back to the dawn of time – into the glorious whirlpools prominent in the foreground of these images. Even more exciting, we’ll discover how the chemical elements from which we are made were created along the way.” said Professor Rob Ivison, from the UK Astronomy Technology Centre in Edinburgh.
Other quotations from UK scientists involved with SPIRE:-
Dr. Seb Oliver (University of Sussex) said: “These images are fantastic, it is as though we have woken up as super heros with the special power to see the secret side of galaxy formation previously hidden by invisibility cloaks.”
Dr Gillian Wright (STFC – UK Astronomy Technology Centre) said: “All of the hard careful work in building this technically challenging mission has really paid off. To have such stunning clear images and scientific results so early in the mission is fantastically exciting and a wonderful achievement.”
Dr Tanya Lim (STFC – Rutherford Appleton Laboratory) said: “The fact that we get such high quality images, so early in the mission, is a testament to the hard work and excellent standards of a large number of people. It is a superb team effort.”
Dr David Clements (Imperial College, London) said: “These images have a huge amount of astronomy in them – from the distribution of dust in the individual galaxies to the faint unresolved distant galaxies behind them. The power of SPIRE and Herschel is clear. Now we have to get down to using it for new science.”
Professor Peter Ade (Cardiff University) said: “It is spectacular to see how far we have come from the first detections of extragalactic objects in the 1970’s with single pixel instruments to these marvellous images from the SPIRE cameras showing detail equivalent to the best ground based optical telescopes at that time.”
Dr Peter Hargrave (Cardiff University) said: “These images are absolutely stunning. They are terrific payback for all the years of effort put into building such a great instrument.”
More information can be found on the ESA website.