Herschel weighs the key ingredient for making galaxies
24 February 2011
A Herschel/SPIRE image of a region of sky called the "Lockman Hole", one of the areas used for this study, located in the constellation of Ursa Major. The region of sky seen is around 60 times the size of the Full Moon as seen in the sky. This region is almost completely devoid of objects in our Galaxy, making them ideal for studying the distant Universe.
Image Credit: ESA / Herschel / SPIRE / HerMES
A simulation of a region of the Universe, showing the way the dark matter (left) was distributed around 3 billion years after the Big Bang. It forms a cosmic web, with clumps, or halos, where it has collapsed due to gravity. The clumps come in a range of sizes, and the amount of dark matter in each one affects whether it can form galaxies. The right panel shows the dark matter clumps in red, with the clumps which are large enough to form stars highlighted in yellow. The region of space simulated is around 1/3 of the size of the area imaged in the Lockman Hole field.
Image Credits: Virgo Consortium / A. Amblard / ESA
Astronomers have used Europe's Herschel Space Observatory to reveal just how much dark matter it takes to make a galaxy full of stars. The findings are a key step in understanding how dark matter – an invisible substance that pervades our Universe – contributed to the birth of massive galaxies in the early Universe.
Galaxies like our own Milky Way formed billions of years ago from clouds of gas collapsing under gravity. The way in which the gas collapses depends on the amount of dark matter in the neighbourhood.
Prof. Asantha Cooray, UC Irvine in Calif., who lead this new research appearing in the Feb. 24 issue of the journal Nature, said:
"If you start with too little dark matter, then a developing galaxy would peter out. But if you have the just the right amount of dark matter, then a galaxy bursting with stars will pop out."
The right amount of dark matter turns out to be a mass equivalent to around 300 billion Suns. For reference, this is about a third of the amount of dark matter surrounding our Milky Way galaxy.
Herschel – the world’s largest space telescope – launched into space in May 2009. The mission's large, 3.5m telescope detects far-infrared light from a host of objects, ranging from asteroids and planets in our own solar system to faraway galaxies. This research was part of the HerMES project, which uses Herschel to look at these distant galaxies and is led by Seb Oliver, of University of Sussex, and Jamie Bock, of NASA’s Jet Propulsion Laboratory. Herschel is a flagship mission of the UK Space Agency, which funds the UK's involvement in the UK-led SPIRE instrument. Bruno Maffei of the University of Manchester's Jodrell Bank Centre for Astrophysics is part of the HerMES key programme. He tested and selected detectors for the SPIRE instrument whilst working at Cardiff University.
Dr David Parker, Director of Space Science and Exploration at the UK Space Agency, which provides the UK funding for Herschel, said:
"Once again, the Herschel team have pushed the boundaries and brought us another step closer to understanding the complex creation and evolution of our Universe. As always, we’re immensely proud of the outstanding work of our UK scientists who are playing key roles in this world-leading space project. Herschel is a jewel in the UK's space programme."
The team used Herschel to measure infrared light from massive, star-forming galaxies in the distant Universe, using images of two regions of the sky in the constellation of Ursa Major. The huge distance means that light has taken 10-11 billion years to cross the Universe, so the galaxies are seen when the Universe was only around 3 billion years old.
Astronomers think that these and other galaxies formed inside halos, or clumps, of dark matter, and were forming stars hundreds of times more rapidly than galaxies in today’s Universe. The rapid star formation produced a lot of interstellar dust, which is what is glowing at the far-infrared wavelengths observed by Herschel.
Dr. Alexandre Amblard, of UC Irvine, lead author of the Nature paper, said:
"This measurement is important because we are homing in on the very basic ingredients in galaxy formation. In this case, the ingredient, dark matter, happens to be an exotic substance that we still have much to learn about."
In this new study, Hershel was able to uncover more about how this galaxy-making process works by acquiring maps of the infrared light that comes from collections of very distant, massive star-forming galaxies. The most distant galaxies are so far away that Herschel cannot see them individually, but rather sees the pattern as their light blurs together. This pattern of light, called the cosmic infrared background, is like a web that spreads across the sky. Because Herschel can survey large areas of the sky very quickly with high resolution, it was able to create the first detailed maps of the cosmic infrared background.
Dr. Jamie Bock, of the Jet Propulsion Laboratory, California, said:
"It turns out that it's much more effective to look at these patterns rather than the individual galaxies. This is like looking at a picture in a magazine from a reading distance – you don’t notice the individual tiny dots but you see the big picture. Herschel gives us the big picture of these distant galaxies, showing the influence of dark matter."
Normal matter – the stuff that makes up people, planets, stars and galaxies – is far outweighed by dark matter. There is around 5 times as much dark matter as normal matter in the Universe, and while it can’t be seen by any telescope, it does give a gravitational tug on the matter we can see.
Giant clumps of dark matter act like gravitational wells to collect gas and dust needed for making galaxies. The gas and dust become much denser as they fall into the well, allowing new stars to form. When there are eventually enough stars, a galaxy is born.
But this only happens if there is enough dark matter to keep the gas and dust clumped together – if there is enough dark matter, several galaxies will form in the same clump. The maps showed that the galaxies are more clustered into groups than previously believed, which means that they tend to lie in larger clumps of dark matter – in those clumps which contain more matter than around 300 billion Suns.
Prof. Seb Oliver, from the University of Sussex, said:
"I find it amazing that with these results we are able to understand the link between mass and star formation, particularly when the mass can never be seen, the star-formation is shrouded in dust and invisible to normal telescopes, and only 15% of the dust emission can be resolved into individual galaxies – heroic work!"
Note for editors:
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Since launch on 14th May 2009, Herschel spent several months undergoing careful tests on the performance of the instruments and calibration. This was followed by the Science Demonstration Phase: the period when the instruments were tested to their full capabilities.
The SPIRE instrument contains an imaging photometer (camera) and an imaging spectrometer. The camera operates in three wavelength bands centred on 250, 350 and 500 μm, and so can make images of the sky simultaneously in three sub-millimetre "colours". The spectrometer covers the range 200–670 μm, allowing the spectral features of atoms and molecules to be measured. SPIRE was designed and built by an international collaboration, led by Professor Matt Griffin of Cardiff University.
HerMES is the Herschel Multi-tiered Extragalactic Survey, an astronomical project to study the evolution of galaxies in the distant Universe. It is the largest project on ESA's Herschel Space Observatory. The project is carried out by a large team, made up primarily of people who built one of the instruments on Herschel called SPIRE. Hermes is also the Olympian messenger god, ruler of travelers, boundaries, weights and measures.
HerMES maps large regions of the sky using cameras that are sensitive to infrared radiation. We expect to discover over 100 thousand galaxies. The light from most of these galaxies will have taken more than 10 billion years to reach us, which means we will see them as they were 3 to 4 billion years after the big bang. Since the cameras are detecting infrared radiation they see star formation that is hidden from conventional telescopes. We expect that our cameras will catch many of the galaxies at the moment they are forming most of their stars.
Dr Bruno Maffei of the Jodrell Bank Centre for Astrophysics (JBCA) is part of the HerMES key programme. He was involved in the design and test of the SPIRE instrument on HERSCHEL when working at Cardiff University, more specifically on the detector test and selection. He is now working at the University of Manchester on the development of instrumentation for future far-infrared to radio astronomical experiments within the Radio Astronomy Technology Group at JBCA.
Further informationFor more information, please see:
For more information please contact
Dr Bruno Maffei,
Jodrell Bank Centre for Astrophysics
School of Physics & Astronomy
University of Manchester
Prof. Seb Oliver,
Dept. of Physics & Astronomy
University of Sussex
+44 (0)1273 678852 / +44 (0)7971 019161
Dr Chris North,
School of Physics and Astronomy,
Cardiff CF42 3AA
+44 (0)129 208 70537
Prof. Asantha Cooray,
University of California, Irvine
+1 (0)949 824 6832
Dr Alexandre Amblard,
University of California, Irvine
+1 (0)415 294 1882
Julia Short, Press Officer, STFC and UKSA
Email: Julia.short [@] stfc.ac.uk
Tel: +44 (0)1793 442 012
Dr Göran Pilbratt, Herschel Project Scientist
European Space Agency
Noordwijk, The Netherlands
Email: gpilbratt [at] rssd.esa.int
Tel: +31 (0)71 565 3621