Sussex ‘eyeball squad’ helps survey the skies in hunt for dark energy
First-year Physics students at the University of Sussex gave up their summer sunshine to study the stars as part of a major international cosmology survey that began this week (03 September 2013).
The 12 students – led by Sussex astrophysicists Dr Marisa March and Dr Kathy Romer – formed part of an “eyeball squad” that studied thousands of test images produced by a new super-camera. The students were searching for anomalies in the images during the run-up to the launch of the Dark Energy Survey (DES).
People, rather than computers, are better for this task as only human eyes and brains can spot unpredicted patterns and inconsistencies – but it means putting in many long hours, staring at computer screens.
DES is a five-year mission (beginning in September 2013) to collect images of millions of galaxies, constellations and exploding stars called supernovae, as they evolve across billions of light years.
To do this, scientists are using the world’s most powerful digital camera (the Dark Energy Survey Camera – a 570-megapixel digital camera that includes five lenses, the largest nearly a metre across, that together provide sharp images over its entire field of view) and the giant Blanco 4m telescope at the Cerro Tololo Inter-American Observatory in the Atacama desert in Chile.
Scientists will use the images gathered to systematically map one-eighth of the sky (5,000 square degrees) in unprecedented detail. The start of the survey is the culmination of ten years of planning, building, and testing by scientists from 25 institutions in six countries, including a team at the University of Sussex.
The survey’s goal is to address some of the fundamental questions of astronomy and physics: why the expansion of the Universe is speeding up, instead of slowing down due to gravity as it should be according to Einstein’s theory of General Relativity, and whether this cosmic acceleration is being caused by the mysterious force known as dark energy.
Dr March says: “Dark energy cannot be seen directly. Instead we look for the effect that dark energy has on other objects in the Universe, such as supernovae and galaxies.
“If you look out of the window, you cannot see the wind, but you can see a flag flying and the trees swaying, so you know the wind is there. So for DES we will be using the Dark Energy Camera to look deep into the Universe at the pattern that galaxies make as they are distributed through the Universe – the brightness of supernovae, the slightly distorted shapes of distant galaxies and the clustering of galaxies. Taken together, all of these signs point to the presence of dark energy. Just like the wind, we cannot see it, but we can see the effect it has on the things around it.
“During this past year some of our students have been checking the 150-300 pictures taken every night of the sky to ensure that they are high quality with no anomalies caused by stray light casting patterns across the picture and no electronic glitches giving strange effects.
“Looking at these images was careful and painstaking work, very time consuming and sometimes very tedious, but it did have its rewards - scanning across these images one can see a wealth of tiny far away galaxies, each one beautiful and different, each one perhaps previously unseen by human eyes.”
Student Rhys Poulton was one of the first-year undergraduate “eyeballers”. He says: “For me, being at university is not just about getting my degree. I wanted to gain skills which cannot be taught in lectures or workshops, so this project gave me a great opportunity to do that. I wanted to be involved so I could be part, however small, of something big. It’s a field of physics I’m passionate about – and this is a project I might want to be involved with in the future, so this has been a brilliant experience.”
During the next four years, DES member Dr Romer and her students will be counting clusters of galaxies1, while Dr March will be examining DES supernovae2. Both will be using colour images that will be produced by DES of 300 million galaxies, 100,000 galaxy clusters and 4,000 new supernovae, many of which were formed when the universe was half its current size.
Dr March, who will now be moving to America to work on another dark energy project called EUCLID adds: “For me this has been a great opportunity to work with our students at Sussex. It’s exciting being part of such a fantastic international project and it's great that some of our students have been able to share in that and have a chance to work with real data.”
Dr Romer, who researches galaxy clusters and their role in the structure of the Universe, says: “I was delighted by the response of our students. It is testament to their dedication and curiosity that so many of them were prepared to give up their free time to support an astronomy project based half way across the world.”
Notes for Editors
The Dark Energy Survey (DES) is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 120 scientists from 23 institutions in the United States, Spain, the United Kingdom, Brazil, and Germany are working on the project. DES will survey a large swath of the southern sky out to vast distances in order to provide new clues to this most fundamental of questions.
For further details and quotes see also press releases from the U.S. Department of Energy’s Fermi National Accelerator Laboratory and the UK funders the Science and Technology Funding Council.
The DES scientists will be:
1 Counting galaxy clusters: While gravity pulls mass together to form galaxies, dark energy pulls it apart. The Dark Energy Camera will see light from 100,000 galaxy clusters billions of light years away. Counting the number of galaxy clusters at different points in time sheds light on this cosmic competition between gravity and dark energy.
2 Measuring supernovae: A supernova is a star that explodes and becomes as bright as an entire galaxy of billions of stars. By measuring how bright they appear on Earth, we can tell how far away they are. Scientists can use this information to determine how fast the universe has been expanding since the star’s explosion. The survey will discover 4,000 of these supernovae, which exploded billions of years ago in galaxies billions of light years away.
The bending of light: When light from distant galaxies encounters dark matter in space, it bends around the matter, causing those galaxies to appear distorted in telescope images. The survey will measure the shapes of 200 million galaxies, revealing the cosmic tug of war between gravity and dark energy in shaping the lumps of dark matter throughout space.
Using sound waves to create a large-scale map of expansion over time: The interplay between matter and light that occurred when the Universe was less than 400,000 years old set off a series of sound waves traveling at nearly two-thirds the speed of light. Those waves left an imprint on how galaxies are distributed throughout the universe. The survey will measure the positions in space of 300 million galaxies to find this imprint and use it to infer the history of cosmic expansion.
The Dark Energy Survey is supported by funding from the U.S. Department of Energy Office of Science; the National Science Foundation; funding agencies in the United Kingdom, Spain, Brazil, Germany and Switzerland; and the participating institutions.
Images and videos
Includes photos of (and taken by) the Dark Energy Camera, a 4-minute video produced at Fermilab detailing the Dark Energy Survey.
Allows the user to see the resolution the Dark Energy Camera is capable of, using a snapshot of the Fornax constellation.
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