Study explains why galaxies stop creating stars

Study explains why galaxies stop creating stars
ESO 137-001 is a perfect example of a spiral galaxy zipping through a crammed cluster of galaxies. Gas is being pulled from its disc in a process called ram pressure stripping. The galaxy appears to be losing gas as it plunges through the Norma galaxy cluster. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).

Galaxies come in three main shapes - elliptical, spiral (such as the Milky Way) and irregular. They can be massive or small. To add to this mix, galaxies can also be blue or red. Blue galaxies are still actively forming stars. Red ones mostly are not currently forming stars, and are considered passive.

The processes that cause to "quench," that is, cease , are not well understood, however, and constitute an outstanding problem in the study of the evolution of galaxies. Now, using a large sample of around 70,000 galaxies, a team of researchers led by University of California, Riverside astronomers Behnam Darvish and Bahram Mobasher may have an explanation for why galaxies stop creating stars.

The research team, which included scientists at the California Institute of Technology and Lancaster University, United Kingdom, combed through available data from the COSMOS UltraVISTA survey that give accurate distance estimates for galaxies over the past 11 billion years, and focused on the effects of external and internal processes that influence star formation activity in galaxies.

External mechanisms, the research team notes, include drag generated from an infalling galaxy within a cluster of galaxies, which pulls gas away; multiple gravitational encounters with other galaxies and the dense surrounding environment, resulting in material being stripped away from the galaxy; and the halting of the supply of cold gas to the galaxy, thus strangling the galaxy of the material needed to produce new stars over a prolonged period of time.

The researchers explain that internal mechanisms include the presence of a black hole (in which jets, winds, or intense radiation heat up hydrogen gas in the galaxy or blow it out completely, thus preventing the gas from cooling and contracting to form stars) and "stellar outflow" (for example, high-velocity winds produced by massive young stars and supernovae that push the gas out of the host galaxy).

"By using the observable properties of the galaxies and sophisticated statistical methods, we show that, on average, external processes are only relevant to quenching galaxies during the last eight billion years," said Darvish, a former graduate student in the UC Riverside Department of Physics and Astronomy and the first author of the research paper that appears today in The Astrophysical Journal. "On the other hand, internal processes are the dominant mechanism for shutting off star-formation before this time, and closer to the beginning of the universe."

Study explains why galaxies stop creating stars
UC Riverside astronomers Behnam Darvish (left) and Bahram Mobasher. Credit: University of California, Riverside.

The finding gives astronomers an important clue towards understanding which process dominates quenching at various cosmic times. As astronomers detect quenched non-star-forming galaxies at different distances (and therefore times after the Big Bang), they now can more easily pinpoint what quenching mechanism was at work.

In astronomy, much debate continues on whether it is only internal, external or a combination of both phenomena that makes a galaxy quench star formation. It is still not clear what processes are mostly responsible, and unclear, too, is the fractional role of different physical processes in shutting down the star-formation. It is also not fully understood when these processes come to play an important role in the evolutionary life of galaxies.

"The situation becomes more complex when we realize that all these mechanisms may depend on properties of galaxies being quenched, they may evolve with time, they act at different time-scales - fast or slow - and they may depend on the properties of the quenching factors as well," Darvish said.

Mobasher, a professor of physics and astronomy who supervised Darvish during the course of the research, said, "We found that on average the external processes act in a relatively short time-scale, around one billion years, and can more efficiently quench galaxies that are more massive. Internal effects are more efficient in dense clusters of galaxies. The time-scale is very important. A short time-scale suggests that we need to look for external physical processes that are fast in quenching. Another important result of the work is that internal and external processes do not act independently of each other in shutting-off the star formation."

Darvish and Mobasher were joined in the research by David Sobral at Lancaster University, the United Kingdom; and Alessandro Rettura, Nick Scoville, Andreas Faisst and Peter Capak at the California Institute of Technology. Darvish graduated from UCR with a Ph.D. in astronomy in 2015. The bulk of the research was done while he was working toward his doctoral degree. He is now a postdoctoral scholar at Caltech.

Next, the research team will work on extending this study to the environment of galaxies on much larger scales (in the cosmic web).


Explore further

Image: Hubble uncovers a mysterious dwarf galaxy

More information: Behnam Darvish et al. THE EFFECTS OF THE LOCAL ENVIRONMENT AND STELLAR MASS ON GALAXY QUENCHING TO∼ 3, The Astrophysical Journal (2016). DOI: 10.3847/0004-637X/825/2/113
Journal information: Astrophysical Journal

Citation: Study explains why galaxies stop creating stars (2016, July 8) retrieved 13 October 2019 from https://phys.org/news/2016-07-galaxies-stars.html
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Jul 08, 2016
Milky Way has over 75% of the red star (https://en.wikipe...ication)
and we are witnessing that in him formed stars.
Maybe the authors do not recognize well colors or evidence.

Jul 08, 2016
"On the other hand, internal processes are the dominant mechanism for shutting off star-formation before this time, and closer to the beginning of the universe."

Sampling bias. Early distant galaxies that are even observable are more likely the bigger grown galaxies, where the central core has grown big and active to blow out the central region.
Another important result of the work is that internal and external processes do not act independently of each other in shutting-off the star formation.

Merger maniacs banging away at stuffing square pegs....Afterall, they need 'some' conclusion, right or wrong.

That galaxy in the photo clearly is producing new gas ejected in the long trailing tale. Just too much of it, even by eyeball. This is why I have lost faith in astronomers. Dumb and dumber.


Jul 08, 2016
Merger maniacs banging away at stuffing square pegs...
Very cool galaxy merger images

In view of that, what do you have to say for yourself, Tuxford?

Jul 08, 2016
producing new gas
Errr, from where?

Is conservation of mass one of those "sciencey" things you don't quite get?

Jul 09, 2016
producing new gas
Errr, from where?

Is conservation of mass one of those "sciencey" things you don't quite get?


"The Creation continued on the eighth day.." http://www.svemir....html#6b

Jul 09, 2016
producing new gas
Errr, from where?

Is conservation of mass one of those "sciencey" things you don't quite get?

Nope. Doc. Your view is too limited. That is where science is stuck. It's the law. Nature is not Texas. Don't be the sheriff.

Open your view. Our 'observable' universe is simply a subset a more comprehensive structure in which we swim. We are the salt in the ocean. The new matter comes from the unobservable part in which we exist. It transforms into a propagating transmutation reaction (as the fire is lit) that we label a particle of matter. Under the right conditions (like inside dense cores of stars) the other elementals in the ocean become salt, and enter our observable subset.

But thanks for asking. Hang onto that gun.

Jul 09, 2016
Your view is too limited.
By conservation of mass, first discovered in the eighteenth century?

Pull the other leg.

Jul 09, 2016
Your view is too limited.
By conservation of mass, first discovered in the eighteenth century?

Pull the other leg.

You have no chance. Can't conceive of the inconceivable, being bound by the rules of the eighteenth century. No imagination allowed.

This all stems from the relatively new science of General Systems theory. Without a considerable background in said science, you have no chance. I have many years in the aerospace controls systems engineering side, so after a year of consideration, I finally go it.

Without said experience, you have no chance. Give it up.

Jul 10, 2016
Great, now the troll claims to be a systems engineer.

Dear troll: I make a living and have made a career as a systems engineer and you wouldn't know a system theory if it jumped up and bit you on the azz.

Violating the Law of Conservation of Mass is no part of systems theory and never was.

Get over it.

Jul 10, 2016
Can't read huh. I never said it violated the conservation LAWS. Can't think either, the lot of you. As I said, you likely will never wake up until someone of higher authority instructs you to do so. So much for you precious scientific method. My words are wasted on the ignorant.

Jul 10, 2016
I never said it violated the conservation LAWS.
Yes, you did. You said:

The new matter comes from the unobservable part in which we exist.
There isn't any "new matter." "New matter" violates the Law of the Conservation of Mass.

Never mind the fact that where we exist is blatantly obviously the observable part. You know, like, by definition. And stuff.

Please don't attempt to get away with technobabble on the physics web site. There are too many people here who know what it would actually mean if it made any sense. And too many who know it doesn't.

Jul 10, 2016
Consider our observable universe to be an open system, rather than closed. The greater ocean of the constituent components of matter are already there, just not detectable. When they begin to combine in a self-sustaining reaction, the reaction becomes observable. Matter is seemingly created. It is rather quite simple. The diffusive constituents are everywhere but far too small to be detectable.

Tell us, what is the smallest 3D particle composed of, anyway?

Jul 10, 2016
what is the smallest 3D particle composed of
Multiple category errors; more technobabble.

1. What's "smallest" mean when we can't put a lower limit on the size of particles?
2. What's a "3D particle?"
3. What's "composed of" mean for a fundamental particle?

And to top it all off, what's all that got to do with conservation of mass?

Jul 10, 2016
Hi Da Schneib, Phys1 and Tuxford. :)

@Da Schneib and @Phys1:

Your attacks on the logic/science validity of Tuxford's claims would carry more weight if they also recognized the same flaws in the claims of mainstream hypothesized 'dark energy' source/effects and 'dark matter' non-baryonic nature. :)

In other words, how can you fault Tuxford's claims that non-baryonic stuff exists but unobservable?

That is exactly mainstream's description/claim for 'dark matter'!

And what about 'dark energy' supposedly INCREASING, causing claimed 'accelerating cosmological expansion'?

That mainstream claim basically violates energy-mass conservation laws!

And as for "smallest" conventional fundamental "particle"; mainstream has identified it as Electron/Positron; 'below' which 'smallest/lowest' rest-energy/mass feature there is no observable 'smaller/lower' particle!

I appreciate your war against pseudo-science/-logics, but try to stick to science/logics in your own critiques. :)

Jul 10, 2016
And as for "smallest" conventional fundamental "particle"; mainstream has identified it as Electron/Positron; 'below' which 'smallest/lowest' rest-energy/mass feature there is no observable 'smaller/lower' particle!
Just curious, how much bigger is a photon? How much bigger is a neutrino? What units are you using to quantify "smallest"? In future, maybe if you capitalized the nouns and used exclamation points, people would accept what you say unquestioningly.

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