Astronomers have detected a massive, sprawling, churning galaxy cluster that formed only 3.8 billion years after the Big Bang. The cluster, shown here, is the most massive cluster of galaxies yet discovered in the first 4 billion years after the Big Bang. Credit: NASA, European Space Agency, University of Florida, University of Missouri, and University of California
Formed only 3.8 billion years after the Big Bang it is 10 billion light yrs from Earth and potentially comprising thousands of individual galaxies, the megastructure is about 250 trillion times more massive than the sun, or 1,000 times more massive than the Milky Way galaxy. The cluster, IDCS J1426.5+3508 (or IDCS 1426), is the most massive cluster of galaxies yet discovered in the first 4 billion years after the Big Bang.
IDCS 1426 appears to be undergoing a substantial amount of upheaval: The researchers observed a bright knot of X-rays, slightly off-center in the cluster, indicating that the cluster’s core may have shifted some hundred thousand light years from its center. The scientists surmise that the core may have been dislodged from a violent collision with another massive galaxy cluster, causing the gas within the cluster to slosh around.
Such a collision may explain how IDCS 1426 formed so quickly in the early universe, at a time when individual galaxies were only beginning to take shape.
Galaxy clusters are conglomerations of hundreds to thousands of galaxies bound together by gravity. In 2012, scientists using NASA’s Spitzer Space Telescope first detected signs of IDCS 1426 and made some initial estimates of its mass. Both the Hubble and Keck Observatories recorded optical data from the cluster, which the researchers analyzed to determine the amount of light that was bending around the cluster as a result of gravity – gravitational lensing. The more massive the cluster, the more gravitational force it exerts, and the more light it bends. They also examined X-ray data from the Chandra Observatory to get a sense of the temperature of the cluster. High-temperature objects give off X-rays, and the hotter a galaxy cluster, the more the gas within that cluster has been compressed, making the cluster more massive. From the X-ray data, McDonald et al also calculated the amount of gas in the cluster, which can be an indication of the amount of matter – and mass – in the cluster.
Using all 3 methods, the group calculated roughly the same mass – about 250 trillion times the mass of the sun. Now, the team is looking for individual galaxies within the cluster to get a sense for how such megastructures can form in the early universe. “By seeing that incompleteness, we can get a sense for how [clusters] grow. So far, we’ve confirmed about a dozen or so galaxies, but we’re just seeing the tip of the iceberg, really.”
He hopes that scientists may get an even better view of IDCS 1426 in 2018, with the James Webb Space Telescope – an infrared telescope that is hundreds of times more sensitive than the Spitzer Telescope that first detected the cluster.
“People had kind of put away this idea of finding clusters in the optical and infrared, in favor of X-ray and radio signatures,” McDonald says. “We’re now re-emerging and saying it’s actually a fantastic way of finding clusters. It suggests that maybe we need to branch out a little more in how we find these things.”
http://news.mit.edu/2016/most-distant-massive-galaxy-cluster-identified-0107
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