Infrared image of the cluster XMMU J2235.3-2557 taken with Subaru, seen at a distance corresponding to 65 percent of the way back to the Big Bang. Credit: Chris Collins et al., Nature
New research is casting doubt on the prevailing view that the heaviest galaxies in the universe started out small and gained mass by devouring other matter that ventured too close.
Peering at galaxies two-thirds of the way back in time to the Big Bang, an international team of astronomers is suggesting that some of the giants we see today were just as massive in that earlier age as they are now.
The new findings were released today in the journal Nature.
Lead author Chris Collins, an astronomer at the United Kindgdom’s Liverpool John Moores University, and his colleagues made their discovery using one of the largest optical telescopes in the World, called Subaru (named after the Japanese word for the Pleiades star cluster), located on the Island of Hawaii and owned by the National Observatory of Japan.
They focused on brightest cluster galaxies (BCGs), located at the centers of galaxy clusters. The massive galaxies constitute a separate population from bright elliptical galaxies, and both their predictability and extreme luminosity have motivated their use as standard candles for cosmology, the authors point out.
Analysing the light from these remote galaxies, the astronomers effectively weighed them and found that despite feeding on a constant diet of small galaxies, the heaviest galaxies have not increased their weight over the last 9 billion years. In a universe whose age is 13.7 billion years old, these results spark a debate as to how these galaxies put on so much weight in the first few billion years after the Big Bang.
“Current predictions using simulations run on super computers suggest that at such a young age these galaxies should be only 20 percent of their final weight, so to find galaxies so large suggests that galaxy formation is a much more rapid process than we previously thought,” Collins said, “and perhaps the theories are missing some important physics.”
John Stott, Collin’s colleague at LJMU and a co-author on the paper, said the team was “surprised to find that the largest and brightest galaxies in the Universe have remained essentially unchanged for the last 9 billion years, having grown rapidly soon after the Big Bang.”
One possibility being considered is that the galaxies formed by the collapse of an already massive cloud at the dawn of the universe.
MORE ABOUT LEAD IMAGE: The image shows the central 1.5 x 1.5 arc min of the cluster corresponding to 0.75 Mpc at this distance. The clusters X-ray emission is used to pinpoint the location of the brightest galaxy in the cluster as shown by the green contours which represent the X-ray intensity as measured by the XMM-Newton X-ray satellite.
Source: LJMU’s Astrophysics Research Institute
