New images of the Spiderweb protocluster of galaxies reveal an unusually high number of active supermassive black holes.
Data from the Chandra X-ray Observatory collected over 8 days show that, in the volume of surveyed space, 14 black holes at the hearts of the galaxies, including the Spiderweb Galaxy at the center of the protocluster, are hungrily devouring material from the space around them.This is a much higher rate than other, similar volumes of space, suggesting that up to a quarter of the most massive galaxies in the baby cluster are bound by actively growing black holes.
Studying such clusters while they are still in the early stages of assembling should yield insights into the evolution of the large-scale structure of the Universe. It can also tell us more about the processes that affect star formation rates and supermassive black hole activity in members of galaxy clusters.But we don't actually know how galaxy clusters evolve, so it's difficult to ascertain which groups are genuine protoclusters, and which are unlikely to change.
Although the black holes themselves give off no light, accretion is so energetic that it sends high-energy light blazing across the Universe. This is what the team detected. In a region of space roughly 11.3 million light-years across, 14 of the galaxies in the protocluster were seen to be emitting X-rays, suggesting that their SMBHs are active.This is much higher than other, similar samples of space at the same epoch, with the same range of galaxy masses.
Another possibility, the researchers said, is that the protocluster has somehow retained a large quantity of cold gas, which would be easier for the black holes to accrete than the hot gas we see in nearby galaxy clusters. Or maybe a combination of factors is at play.