An international research team, led by Dr. Bianca Poggianti of the INAF-Astronomical Observatory of Padova, has used the MUSE instrument on ESO’s Very Large Telescope to study how gas can be stripped from so-called ‘jellyfish’ galaxies — galaxies with long ‘tentacles’ of material that extend for dozens of thousands of light-years beyond their galactic disks.
This image of the ‘jellyfish’ galaxy JO204 shows clearly how material is streaming out of the galaxy in long tendrils to the lower-left; red shows the glow from ionized hydrogen gas and the whiter regions are where most of the stars in the galaxy are located; some more distant galaxies are also visible. Image credit: ESO / GASP Collaboration.
‘Jellyfish’ galaxies can be found only in galaxy clusters and are very rare: to date, just over 400 candidate galaxies have been found.
The ‘tentacles’ of these galaxies are produced in galaxy clusters by a process called ram-pressure stripping. Their mutual gravitational attraction causes galaxies to fall at high speed into galaxy clusters, where they encounter a hot, dense gas which acts like a powerful wind, forcing tails of gas out of the galaxy’s disc and triggering starbursts within it.
Six out of the seven jellyfish galaxies observed by Dr. Poggianti and co-authors were found to host a supermassive black hole at the center, feeding on the surrounding gas. This fraction is unexpectedly high — among galaxies in general the fraction is less than one in ten.
“This strong link between ram pressure stripping and active black holes was not predicted and has never been reported before,” Dr. Poggianti said.
“It seems that the central black hole is being fed because some of the gas, rather than being removed, reaches the galaxy center.”
A long-standing question is why only a small fraction of supermassive black holes at the centers of galaxies are active. Supermassive black holes are present in almost all galaxies, so why are only a few accreting matter and shining brightly?
“The MUSE observations suggest a novel mechanism for gas to be funneled towards the black hole’s neighborhood,” said co-author Dr. Yara Jaffé, of ESO.
“This result is important because it provides a new piece in the puzzle of the poorly understood connections between supermassive black holes and their host galaxies.”
“A long-standing puzzle in astronomy has been to understand how galaxies form and change in our expanding and evolving Universe,” Dr. Poggianti said.
“Jellyfish galaxies are a key to understanding galaxy evolution as they are galaxies caught in the middle of a dramatic transformation.”
The findings appear in the August 17, 2017 issue of the journal Nature.
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Bianca M. Poggianti et al. 2017. Ram-pressure feeding of supermassive black holes. Nature 548: 304-309; doi: 10.1038/nature23462
