It looks like a bunch of slightly blurry, multicoloured fireflies, but while the image above doesn't look impressive at first glance, it certainly improves on more intimate acquaintance. It's actually a whole bunch of black holes at the centres of galaxies, imaged by NASA's Chandra X-ray Observatory.
To be more precise, it's over 1,000 black holes, in a patch of sky around two-thirds the size of the full moon in the southern constellation of Fornax. A patch of sky the size of the full moon at this concentration would contain 5,000 black holes; the entire sky would contain a billion.
"With this one amazing picture, we can explore the earliest days of black holes in the Universe and see how they change over billions of years," said study leader Niel Brandt, the Verne M. Willaman Professor of Astronomy and Astrophysics and professor of physics at Pennsylvania State University.
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The colours represent x-rays. Red shows low-energy x-rays, green for medium-energy and blue for high-energy. These x-ray emissions come from over 2,000 galaxies. Capturing the image took over 7 million seconds of exposure time over 102 sessions, stacking the data and cross-referencing it against the Hubble Ultra Deep Field, which shows the same region.
The aim of this research was to study the formation of black holes in the early universe, and they're all from the universe's infancy, at distances from Earth between 11.9 and 12.9 billion light-years. This study, presented at the American Astronomical Society on January 5, 2017 and available to read on arXiv, revealed that early universe black holes grew in short, powerful bursts rather than building slowly.
They also found that the "seeds" for these black holes are extremely massive, coming in at 10,000 to 100,000 times the mass of the sun. This could help solve the mystery of how black holes a billion times the mass of the sun can exist in the early universe. Previously, these supermassive black holes challenged the models for black hole growth, but if they start from a much larger "seed", the growth rate doesn't need to be so high.
Further research, using data from Chandra and future observations, is required to solve this mystery once and for all.