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

February 25, 2014 by Elizabeth Howell
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."

Explore further: Universe's early galaxies grew massive through collisions

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]

Related Stories

Universe's early galaxies grew massive through collisions

January 29, 2014

It has long puzzled scientists that there were enormously massive galaxies that were already old and no longer forming new stars in the very early universe, approx. 3 billion years after the Big Bang. Now new research from ...

Hubble and Galaxy Zoo find bars and baby galaxies don't mix

January 17, 2014

(Phys.org) —Harnessing the power of both the Hubble Space Telescope and the citizen science project Galaxy Zoo, scientists from the University of Portsmouth have found that bar-shaped features in spiral galaxies accelerate ...

Galaxies the way they were

April 3, 2013

(Phys.org) —Galaxies today come very roughly in two types: reddish, elliptically shaped collections of older stars, and bluer, spiral shaped objects dominated by young stars. The conventional wisdom is that the two types ...

Image: Hubble sees a swirl of star formation

May 27, 2013

(Phys.org) —This beautiful, glittering swirl is named, rather un-poetically, J125013.50+073441.5. A glowing haze of material seems to engulf the galaxy, stretching out into space in different directions and forming a fuzzy ...

Recommended for you

Swarm explores a new feature of the northern lights

April 21, 2017

Thanks to social media and the power of citizen scientists chasing the northern lights, a new feature was discovered recently. Nobody knew what this strange ribbon of purple light was, so … it was called Steve.

Detecting life in the ultra-dry Atacama Desert

April 21, 2017

Few places are as hostile to life as Chile's Atacama Desert. It's the driest non-polar desert on Earth, and only the hardiest microbes survive there. Its rocky landscape has lain undisturbed for eons, exposed to extreme temperatures ...

New look at 2004's martian hole-in-one site

April 21, 2017

A new observation from NASA's Mars Reconnaissance Orbiter (MRO) captures the landing platform that the rover Opportunity left behind in Eagle Crater more than 13 years and 27 miles (or 44 kilometers) ago.


Adjust slider to filter visible comments by rank

Display comments: newest first

1.6 / 5 (7) 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.
5 / 5 (5) 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.
5 / 5 (5) 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.
5 / 5 (5) 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
This comment has been removed by a moderator.
Feb 26, 2014
This comment has been removed by a moderator.
Feb 26, 2014
This comment has been removed by a moderator.
5 / 5 (2) 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.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.