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A Galaxy Murder Mystery

Last Updated on Tuesday, 17 January 2017 11:01
Published on Tuesday, 17 January 2017 11:01

It’s the big astrophysical 'whodunnit'. Across the Universe, galaxies are being killed and the question scientists want answered is, "What’s killing them?"

GALAXY-STRIPPING-3 smallAn artist’s impression showing the increasing effect of ram-pressure stripping in removing gas from galaxies, sending them to an early death. Credit: ICRAR, NASA, ESA, the Hubble Heritage Team (STScI/AURA). Click for a full size imageNew work published today in the journal Monthly Notices of the Royal Astronomical Society, by a global team of researchers based at the International Centre for Radio Astronomy Research (ICRAR) in Australia, seeks to answer that question. The study reveals that a phenomenon called ram-pressure stripping is more prevalent than previously thought, driving gas from galaxies and sending them to an early death by depriving them of the material to make new stars.

The research used an innovative technique combining the largest optical galaxy survey ever completed—the Sloan Digital Sky Survey—with the largest set of radio observations for atomic gas in galaxies —the Arecibo Legacy Fast ALFA survey.

The study of 11,000 galaxies shows that their gas—the lifeblood for star formation—is being violently stripped away on a widespread scale throughout the local Universe.

Toby Brown, leader of the study and PhD candidate at ICRAR and Swinburne University of Technology, said the image we paint as astronomers is that galaxies are embedded in clouds of dark matter that we call dark matter halos.

Dark matter is the mysterious material that, despite being invisible, accounts for roughly 27 per cent of our Universe, while ordinary matter makes up just 5 per cent. The remaining 68 per cent is the even more mysterious dark energy.

"During their lifetimes, galaxies can inhabit halos of different sizes, ranging from masses typical of our own Milky Way to halos thousands of times more massive," said Mr Brown.

"As galaxies fall through these larger halos, the superheated intergalactic plasma between them removes their gas in a fast-acting process called ram-pressure stripping.

"You can think of it like a giant cosmic broom that comes through and physically sweeps the gas from the galaxies."

Mr Brown said removing the gas from galaxies leaves them unable to form new stars:

"It dictates the life of the galaxy because the existing stars will cool off and grow old. If you remove the fuel for star formation then you effectively kill the galaxy and turn it into a dead object."

ICRAR researcher Dr Barbara Catinella, co-author of the study, said astronomers already knew ram-pressure stripping affected galaxies in clusters, which are the most massive halos found in the Universe.

"This paper demonstrates that the same process is operating in much smaller groups of just a few galaxies together with much less dark matter,” added Mr Brown.

"Most galaxies in the Universe live in these groups of between two and a hundred galaxies. We’ve found this removal of gas by stripping is potentially the dominant way galaxies are quenched by their surroundings, meaning their gas is removed and star formation shuts down."

Mr Brown said the other main process by which galaxies run out of gas and die is known as strangulation.

"Strangulation occurs when the gas is consumed to make stars faster than it’s being replenished, so the galaxy starves to death. It’s a slow-acting process. On the contrary, what ram-pressure stripping does is bop the galaxy on the head and remove its gas very quickly—of the order of tens of millions of years—and astronomically speaking that’s very fast."

An animation showing how ram-pressure stripping removes gas from galaxies, sending them to an early death. Credit: ICRAR, NASA, ESA, the Hubble Heritage Team (STScI/AURA)


Further information

The research appears in "Cold gas stripping in satellite galaxies: from pairs to clusters",
T. Brown, B. Catinella, L. Cortese, C del P. Lagos, R. Davé, V. Kilborn, M. P. Haynes, R. Giovanelli and M. Rafieferantsoa, Monthly Notices of the Royal Astronomical Society, vol. 466, 2, April 2017.

The International Centre for Radio Astronomy Research (ICRAR) is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia.

See also the full set of multimedia resources for this release.


Media contact

Pete Wheeler
Tel (Australia): +61 423 982 018
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Science contacts

Mr Toby Brown
ICRAR-UWA, Swinburne University of Technology
Tel (Australia): +61 08 6488 7753
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Dr Barbara Catinella
Tel (Australia): +61 08 6488 7760
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Notes for editors

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