Ellipticals and spirals comprise two different populations of "green" galaxies

Ellipticals and spirals comprise two different populations of “green” galaxies
M33, the Triangulum Spiral Galaxy, seen here in a 4.3 hour exposure image. Credit: John Chumack.

We keep saying this: the universe is more complex than it appears. Conventional thinking in galaxy research postulates that spiral galaxies have star-forming areas, while ellipticals do not due to a lack of gas. While this thinking has been debunked, there's now emerging research showing a "green valley" of galaxies somewhat in between these two types.

Basically, the research (which includes participation from citizen scientists in the Galaxy Zoo project) is showing that there are two different populations of "green" galaxies, between ellipticals and spirals. Further, the research demonstrates what happens to based upon gas in the area.

"In this paper, we take a look at the most crucial event in the life of a galaxy: the end of star formation. We often call this process 'quenching' and many astrophysicists have slightly different definitions of quenching. Galaxies are the place where cosmic gas condenses and, if it gets cold and dense enough, turns into . The resulting stars are what we really see as traditional optical astronomers," wrote Kevin Schawinski, a Ph.D. student at the University of Oxford who is on the Galaxy Zoo team, in a blog post.

"Not all stars shine the same way though: stars much more massive than our sun are very bright and shine in a blue light as they are very hot. They're also very short-lived. Lower mass stars take a more leisurely pace and don't shine as bright (they're not as hot). This is why star-forming galaxies are blue, and quiescent galaxies (or 'quenched' ) are red: once star formation stops, the bluest stars die first and aren't replaced with new ones, so they leave behind only the longer-lived red stars for us to observe as the galaxy passively evolves."


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More information: "The Green Valley is a Red Herring: Galaxy Zoo reveals two evolutionary pathways towards quenching of star formation in early- and late-type galaxies." Kevin Schawinski, C. Megan Urry, Brooke D. Simmons, Lucy Fortson, Sugata Kaviraj, William C. Keel, Chris J. Lintott, Karen L. Masters, Robert C. Nichol, Marc Sarzi, Ramin, Skibba, Ezequiel Treister, Kyle W. Willett, O. Ivy Wong, Sukyoung K. Yi. arXiv:1402.4814 [astro-ph.GA]
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Citation: Ellipticals and spirals comprise two different populations of "green" galaxies (2014, February 25) retrieved 21 May 2019 from https://phys.org/news/2014-02-ellipticals-spirals-comprise-populations-green.html
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Feb 25, 2014
More nonsense based on flawed assumptions that blue stars are short-lived. Big hot blue can be older, very active stars growing rapidly from within (like plants for the simple-minded).

Yes, spirals evolve into ellipticals, growing all the way (like plants). So an intermediate state of galaxy could be classified — for those who thrive on classifications, which might make them feel intellectual.

Maybe astronomers need to take a few biology courses! Might gain some insight. Otherwise, they will just remain dumb and confused.

Feb 25, 2014
Maybe astronomers need to take a few biology courses! .


Oh yeah, I think ya might be on to something. I see the potential for a new cosmological paradigm there.

Feb 26, 2014
Maybe biologists need to take a few astrophysics courses (starting with thermodynamics and conservation of energy) before commenting on topics they don't understand. Otherwise, they will just remain a source of endless amusement for the rest of the readers.

Feb 26, 2014
Yes, spirals evolve into ellipticals, growing all the way (like plants).


Until they split into two or more baby galaxies, like single cell organisms dividing to multiply? Or do they lay eggs, which are actually the dwarf galaxies we see around the larger ones?

Yeah, that kinda makes sense, since we know from EU/PC theory that the laws of thermodynamics are complete nonsense. We've actually got the whole entropy thing backwards.

Just one question: Do you do your astronomical observations with papers or a bowl?

Feb 26, 2014
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Feb 26, 2014
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Feb 26, 2014
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Feb 27, 2014
Bonia, that's an aweful lot of conjecture and junk science. Really too much wrong with it to bother discussing. To be an effective troll, you need to focus on a smaller number if ideas, so that people are tempted into responding.

However, you did almost accidentally stumble onto some real science that isn't off topic.

The relative number or ratios of different types, sizes, ages, etc. of galaxies tells us some interesting things.

First, the shapes of galaxies don't appear to be random, so they appear to obey the laws of physics, which is a comforting thought.

Second, the vast majority of galaxies that haven't suffered a recent disruption fall into just a handful of shapes, with disks and elipses being far more numerous than other shapes. That tells us that if disks and spirals 'evolve' into elipses over time, then the intermediate stage between the two shapes must not last very long. If it was a slow transition, then we would see lots of in-between galaxies floating around.

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