Galaxy murder mystery

January 17, 2017
This artist's impression shows the spiral galaxy NGC 4921 based on observations made by the Hubble Space Telescope. Credit: ICRAR, NASA, ESA, the Hubble Heritage Team (STScI/AURA)

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

New research published today by a global team of researchers, based at the International Centre for Radio Astronomy Research (ICRAR), seeks to answer that question. The study reveals that a phenomenon called ram-pressure stripping is more prevalent than previously thought, driving gas from and sending them to an early death by depriving them of the material to make .

The study of 11,000 galaxies shows their gas—the lifeblood for —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 that we call .

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 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," Mr Brown said.

"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.

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)

"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," he said.

"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," said Mr Brown.

"Most galaxies in the Universe live in these groups of between two and a hundred galaxies," he said.

An 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)

"We've found this removal of gas by stripping is potentially the dominant way galaxies are quenched by their surrounds, meaning their gas is removed and star formation shuts down."

The study was published in the journal Monthly Notices of the Royal Astronomical Society.

It 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.

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," he said.

"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."

Explore further: Mystery of ultra-diffuse faint galaxies solved

More information: 'Cold gas stripping in satellite galaxies: from pairs to clusters', published in the Monthly Notices of the Royal Astronomical Society on January 17th, 2017. arxiv.org/abs/1611.00896

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11 comments

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RNP
4.3 / 5 (6) Jan 17, 2017
An open access copy of the paper is available here: https://arxiv.org...0896.pdf
dogbert
4.2 / 5 (5) Jan 17, 2017
I can see how high speed intergalactic gas streams could strip a galaxy of it's free gas. Don't understand why the author seeks to make dark matter the culprit. Dark matter is supposed to interact with ordinary matter only gravitationally, so how can it be expected to strip gas from a galaxy?
RNP
3 / 5 (4) Jan 17, 2017
@dogbert
The emphasis on DM IS a little misleading, but the article does specifically state that:

"...the superheated intergalactic plasma between them [galaxies] removes their gas in a fast-acting process called ram-pressure stripping.".

So it is the hot, X-ray emitting gas in the DM halo of the group/cluster that is doing the stripping, not the DM itself.
dogbert
3.3 / 5 (7) Jan 17, 2017
RNP,
My comment was a question on why the author felt the need to confuse the issue with dark matter references. It seems every article about anything to do with astronomical observations has to have the obligatory reference to dark matter on the principle that if you say something often enough, even when the comment has nothing to do with the subject under discussion, people will tend to believe you have said something real.

Imaginary matter did not needed to be references in this context as it has nothing to do with stripping galaxies of their gas.
cantdrive85
1.5 / 5 (12) Jan 17, 2017
Given astrophysicists utter ignorance and complete inability to use real plasma physics, any conclusions reached in this paper are not worth said paper it's written on. It actually makes the papers worthless.
CCMcCombs
1 / 5 (2) Jan 17, 2017
It could also be a highly-advanced machine race of synthetic-organic starships that reside in intergalactic space where they hibernate until the time comes to feed. e.g. Reapers. According to Geth lore, they are the Old Machines.
RNP
3.4 / 5 (5) Jan 17, 2017
@dogbert
Imaginary matter did not needed to be references in this context as it has nothing to do with stripping galaxies of their gas.


The DM is important in this case because without it the gravitational field of the cluster would not be strong enough to hold on to the extremely hot gas that is doing the stripping (which is at 10 million Kelvin or more).
dogbert
2.6 / 5 (5) Jan 17, 2017
RNP,

The hot gas stripping gas from these galaxies is not being held in place by dark matter. It is stripping the gas in those galaxies because it is moving through them taking their gas with them.

NIPSZX
2.5 / 5 (4) Jan 17, 2017
That is crazy that astronomers can time lapse 10 million years of film footage to watch galaxies change over the course of ten million years. How is this possible?
richdiggins
5 / 5 (2) Jan 18, 2017
"am-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"

The question that comes to mind regarding the timescale, is how did the dark matter evolve recently to begin performing these feats.

Shouldn't the dark matter have already killed off all the galaxies when the universe was a lot younger and smaller?
wduckss
3.7 / 5 (3) Jan 18, 2017
"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, as the galaxy starves to death," he said. "

This is physics today. Hitchcock variant.

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