JELLYFISH galaxies are dead ringers for their aquatic namesakes, with blob-like bodies and star-studded tentacles that can be tens of thousands of light years long.
Now it seems these galaxies host highly active supermassive black holes, which may be fed by the same process that gives the galaxies their distinctive tentacles. The black holes are at the centres of the galaxies and tend to devour stars and other matter, says Bianca Poggianti at the Italian National Institute for Astrophysics.
Out of a sample of seven jellyfish galaxies, Poggianti and her team found that six contained huge black holes eating up hot gas from within each galaxy (Nature, ). This suggests there is something about jellyfish galaxies that makes them the ideal feeding ground for supermassive black holes, she says.
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But Alastair Edge at Durham University, UK, isn鈥檛 convinced there are active black holes in the galaxies examined. 鈥淚t鈥檚 an interesting conclusion, but an ambiguous one,鈥� he says, warning that what looks like an active black hole may actually be the traces of a collision between two gas clouds.
Studying jellyfish galaxies could improve our understanding of how galaxies age and why their rate of star formation drops over time, says James Aird at the University of Cambridge.
The tentacles are formed by a process called ram pressure. As a galaxy moves through a dense galaxy cluster, the cluster鈥檚 hot gas blows away the cooler gas in the galaxy. Long chains of stars later form from this cool gas trailing behind.
鈥淪omething about jellyfish galaxies makes them the ideal feeding ground for supermassive black holes鈥�
If enough gas is drawn away from the galaxy鈥檚 body into its starry tentacles, its rate of star formation will slow down, Aird says.
Ram pressure also churns the gas, pushing some of it out of a stable orbit and into the black hole. This may explain why jellyfish galaxies seem more likely than other types of galaxies to have active black holes at their centres.
This article appeared in print under the headline 鈥淕alaxies with tentacles feed black holes鈥�
