The dwarf galaxies orbiting the much larger galaxy Centaurus A appear to be moving along the same plane as one another. If this surprisingly coordinated dance around a galactic hub is common across the cosmos, we may have to go back to the drawing board on galaxy formation theory.
But that鈥檚 a big, big if. Theories on galaxy formation suggest that dwarf galaxies should be captured by larger galaxies into random orbits based on the direction they came from. In this view, large galaxies are like hoarders, snatching up satellite galaxies and tossing them wherever.
In Centaurus A, however, it is more like a collector has neatly put them in a row on a shelf.
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at the University of Basel, Switzerland, led a team who found that 14 out of 16 known satellite galaxies circle Centaurus on the same plane, suggesting that this may be a common phenomenon.
They say this could disrupt commonly held ideas about the mechanisms of galaxy creation. If galaxies are formed from smaller galaxies, there should be a random arrangement of orbits. But a series of objects orbiting in the same direction on the same plane may indicate an entirely different scenario.
Not so random
To help locate the satellite galaxies, the team relied on velocity measurements based on red shift and blue shift: the way light from an object appears to change colour as the object moves away from or towards an observer. If the satellite galaxies seem to head in the same direction on the same plane, it indicates that their position may not be so random.
However, to build an accurate 3D model of the system also requires having a good idea of the satellite galaxies鈥� positions, says at the Carnegie Observatories in California. The paper says there is only a 5 per cent uncertainty about the positions of the satellites, but Beaton thinks that may be too optimistic. To work out how far the galaxies are from Centaurus A, which is somewhere between 10 and 16 million light years away, astronomers look for bright stars that make for easier red-shift and blue-shift measurements. Those numbers give a good ballpark figure of galactic distance, but aren鈥檛 an exact measurement.
Estimating the movements of these galaxies 鈥渋s not impossible at this distance, but is also very hard at any distance and these are sparsely populated dwarf galaxies鈥�, so they provide only a limited number of reference stars, Beaton says.
At 10 per cent uncertainty, the actual alignment and coordination between the dwarf galaxies becomes less pronounced. In effect, if there is too much uncertainty over the distance, it throws a wrench into the certainty of the alignment 鈥� which could mean that we don鈥檛 have to go back to the drawing board quite yet.
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