Astronomers have found mysteriously aligned black holes

Explaining the mystery could tell us more about the early universe

Astrophysical jets are spectacular sights in deep space. The fastest and most powerful are the radio jets emitted from supermassive black holes at the centre of galaxies. It isn’t known exactly how the radio jets are formed or why they tend to occur when galaxies have merged together. More mysteriously, astronomers have recently found a region of the sky where all the black holes and their radio jets are perfectly aligned despite being millions of light years apart.

The researchers at the University of Cape Town and University of the Western Cape were conducting deep radio imaging using the Giant Metrewave Radio Telescope (GMRT). It’s been long known that radio jets can be seen streaming out of galaxies and some are so powerful they’re surely powered by giant black holes. What the astronomers found was a large region of space where radio jets are being spun out in the exact same direction by black holes that are entirely independent and nowhere near each other. Huh?

Jets shooting in the same direction suggest that the galaxies are spinning in the same direction. Why should so many of these jet-emitting galaxies at great distances from each other be spinning the same way? They don’t communicate with each other and they don’t influence each other’s spin. An analogy would be that cyclones in the northern hemisphere always spin the same direction. Do the hurricanes all communicate? No, they’re all affected by something much larger: the spin of the Earth itself. In the northern hemisphere, the Earth spins anti-clockwise and cyclones spin in the opposite direction. All of this is reversed in the southern hemisphere.

Two identical images but the left has circles highlighting the aligned galaxies. Image © Russ Taylor via MNRAS (June 11, 2016) 459 (1): L36-L40. doi: 10.1093/mnrasl/slw038

The astronomers believe that the black holes and their jets share their direction not because of interactions with each other but because they’re all influenced in the same way by something else. The likely culprit? The very formation of those galaxies back when the universe was very young. If the jets are aligned then the galaxies must spin the same way, which suggests something in this large region of space set them all spinning that way in the first place.

In the early universe, there were primordial mass fluctuations that gave rise to the physical structure of the universe we see today. How and why these fluctuations happened is debated but the point is that variations in density in those early times influenced how the entire universe is now structured.

The researchers have suggested that it is those fluctuations during cosmic inflation that caused galaxies in this region of space to spin in the same direction. Today we see evidence of this in the weirdly aligned radio jets shooting from the galaxies. How the fluctuations actually influence the galaxies themselves isn’t known but potential explanations include magnetic fields and even cosmic strings.

Why is this exciting? None of the current theories predict that the spin of galaxies will be aligned like this and that primordial fluctuations could be behind it. When we find something really weird in space, it challenges theories. The more mysterious cosmological phenomena we can explain, the stronger our theories are and the closer we get to understanding the evolution of the early universe.


Main image © NASA/ESA/STScI