Back in time: Researchers identify galaxy clusters from the early universe
An international team of scientists from the UK, US, Europe, Canada and South Africa has discovered four previously unknown galaxy clusters about 10 billion light years from Earth – clusters formed when the universe was less than 4 billion years old. The study was published in the February 2014 issue of Monthly Notices of the Royal Astronomical Society.
Dr Mattia Vaccari of the University of the Western Cape's (UWC) Astrophysics group was part of the team that used a new technique combining data from two satellites to view clusters nearly a billion years older than the oldest clusters previously known. The Planck satellite scanned the whole sky for sources of far infrared emission, and the more sensitive receivers of the Herschel satellite were used to examine those sources more closely at sub-millimetre wavelength. Most of the 16 sources identified by researchers were single galaxies, but four multiple, fainter sources indicated previously unknown galaxy clusters.
Galaxy clusters are perhaps the largest objects in the universe, each containing hundreds or thousands of galaxies held together by gravity. Many nearby galaxy clusters have been identified, but by going further back in time (and looking greater distances away from the Earth) astronomers can gain a better understanding of how clusters are formed.
“Although we're able to see individual galaxies that go further back in time, up to now, the most distant clusters found by astronomers date back to when the universe was 4.5 billion years old. This equates to around nine billion light years away,” says study leader, Dr David Clements, from the Department of Physics at Imperial College London. “Our new approach has already found a cluster in existence much earlier than that, and we believe it has the potential to go even further.”
The team used additional data to estimate the distance of these clusters from Earth, and which of the galaxies within them were forming stars. Unlike the Milky Way, which is a spiral galaxy filled with gas being formed into stars, most clusters today are dominated by elliptical galaxies which have many stars but little gas.
"What we believe we are seeing in these distant clusters are giant elliptical galaxies in the process of being formed,” says Dr Clements.
Dr Vaccari, who worked on the Herschel mission while a research assistant in London with Dt Clements, believes these findings are just a hint of things to come, and that South Africa's MeerKAT and Square Kilometre Array (SKA) telescopes will set the bar even higher in future.
“MeerKAT and the SKA will boost our sensitivity to clusters of galaxies in the early stages of the life of the universe,” he explains. “Young, strongly star-forming galaxies have powerful radio emission, and this will allow us to detect them up to very large distances.”
UWC's Astrophysics Group, headed by SARChI research chairs Prof Roy Maartens and Prof Romeel Dave, has already built up a major presence in the field of astrophysics, with 81 refereed journal papers for 2013 alone. The Astrophysics Group is heavily involved in the Square Kilometre Array (SKA) project, which seeks to build the world's largest array of sensors in the radio wavelengths in South Africa, as well as the equipment to detect it. Most of the Group's 13 post-doctoral researchers and 14 students are supported by the SKA and by the SARChI programme, and this year's March graduation saw several SKA-funded postgraduate students earning their degrees at the University.
The scan-and-zoom multi-satellite technique could be used to identify thousands more galaxy clusters, looking further back in time and helping to build a more detailed timeline of how these clusters are formed.
Who knows what else they may find? The universe is a big place, and there are surely more mysteries waiting to be uncovered.