Spiral galaxies may be dying because of bars

Nov 10, 2010
Spiral galaxies may be dying because of bars

With the help of the army of volunteers working on the Galaxy Zoo 2 'citizen science' project an international team of scientists led by a Portsmouth astrophysicist may have discovered what is killing spiral galaxies.

Dr. Karen Masters, of the University of Portsmouth’s Institute of Cosmology and Gravitation, led the team whose research shows that the bars found in many spiral galaxies, including our own Milky Way, could be helping to kill them off.

The researchers present their results in the journal Monthly Notices of the Royal Astronomical Society.

The overwhelming majority of stars in the universe are found in galaxies like the Milky Way. These vast stellar assemblies contain anything between a few hundred million and one million billion stars and come in a variety of shapes, from irregular to elliptical (shaped like rugby balls) to spirals, where spiral arms wind out in a disk from a central bulge.

About half of these spiral galaxies have a bar – a linear structure of stars crossing the centre. Bars are important for the evolution of galaxies as they provide a way to move material in and out in the disk and possibly help to spark star formation in the central regions. They may even help feed the central massive black hole that seems to be present in almost all galaxies. But bars provide scientists with a great puzzle because it is still not understood why some galaxies have bars and others do not.

The scientists drew on the work of the volunteers taking part in Galaxy Zoo 2, the follow-on from the highly successful project. In this second phase users were asked to make detailed classifications of the galaxies they looked at, including information on the presence of a bar.

With these data – the largest ever sample of galaxies with visual bar identifications – they have shown that red spirals are about twice as likely to host bars as blue spirals. These colors are significant. Blue galaxies get their hue from the hot young stars they contain, implying that they are forming stars in large numbers. In red galaxies, this star formation has stopped, leaving behind the cooler, long-lived stars that give them their red color.

The astronomers conclude that bars might help to kill spiral galaxies, although how they do it remains a mystery.

Dr. Masters sings the praises of the Galaxy Zoo 2 volunteers: “I'm really delighted to publish this first science result from Galaxy Zoo 2. Having so many people involved in this research is wonderful, and I feel a great weight of responsibility to make sure good science comes out of all the hard work they put into classifying galaxies.

“For some time data have hinted that spirals with more old stars are more likely to have bars, but with such a large number of bar classifications we’re much more confident about our results. And all of this is thanks to the dedication of the volunteers who provide the raw ‘clicks’.

“It’s not yet clear whether the bars are some side effect of an external process that turns spiral red, or if they alone can cause this transformation. We should get closer to answering that question with more work on the Galaxy Zoo dataset.”

The volunteers – Zooites – share her enthusiasm. Eric Hobein said: "It’s nice to figure out how we help and be a super-tiny part of it all"; while Mike Tracey said: "I had fun doing my bit and my high school students were involved too. It is great to be part of a real life project which can produce real science."

Explore further: Young binary star system may form planets with weird and wild orbits

More information: The paper “Galaxy Zoo: Bars in Disk Galaxies”, Masters K. L. et al, will appear in the journal Monthly Notices of the Royal Astronomical Society. A preprint can be seen at http://arxiv.org/abs/1003.0449

Provided by University of Portsmouth

4.2 /5 (16 votes)

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User comments : 9

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ThanderMAX
3.7 / 5 (3) Nov 10, 2010
Red galaxy also means more abundant of higher order elements, such as carbon,silicon,nitrogen even yttrium,uranium etc.

So "Red Galaxy" are more hospitable towards life and have higher probability of harboring intelligent life.

Who knows there may be a hyper-intelligent race having million years of technological advances... (I mean old civilization)
KwasniczJ
1 / 5 (4) Nov 10, 2010
On this animation the formation of bar is connected with collision of galaxies, which caused the large perturbation in established path of stars within galaxy.

http://www.galaxy...ion.html
Parsec
3.8 / 5 (4) Nov 10, 2010
Red galaxy also means more abundant of higher order elements, such as carbon,silicon,nitrogen even yttrium,uranium etc.

So "Red Galaxy" are more hospitable towards life and have higher probability of harboring intelligent life.

Who knows there may be a hyper-intelligent race having million years of technological advances... (I mean old civilization)

Not necessarily. The color of stars and the metals content do not directly correlate. The color of stars is directly related to its mass.

Having said that, A red galaxy would have blown up most of its larger stars, so the interstellar medium would probably have a greater percentage of metals.
Decimatus
5 / 5 (1) Nov 10, 2010
The title seems to draw the conclusion that the bar is killing the galaxy "somehow", but the other obvious conclusion would be that galaxies which are already old and dying form this bar structure as a natural part of their age.

Basically the bar isn't killing the galaxy, it would just be a symptom of it's death.

Of course, death is pretty relative here. Have we yet seen a "dead" galaxy? Perhaps a small puff of stars with a 10-100 billion solar mass blackhole at the center?

Or a galaxy inhabited mostly by red giants, black holes, and neutron stars?

I don't think so.

Less exaggeration, more logic and science please.
LivaN
not rated yet Nov 11, 2010
So "Red Galaxy" are more hospitable towards life and have higher probability of harboring intelligent life.


Organic life that is. Advanced life (highly intelligent and technologically advanced) would have a higher probability of being found in the more energetic (blue) galaxies.
A2G
1 / 5 (19) Nov 11, 2010
Parsec wrote:

"The color of stars is directly related to its mass."

Sorry, this is a speculative statement presented as fact. It is circular reasoning that so-called scientists often use.... It is not known with certainty why stars are of different colors...What if it is just because of the matter that was available in their area when they were formed? I can dope a neon bulb with different elements and get different colors..Does that then mean that a red neon bulb is of a different age than a green neon bulb?

Color of stars does not nescessarily mean a different age...This is a theory, not fact.

Remember the "scientists" of this world thought the Earth was flat a mere 500 years ago. They also thought the Earth was the center of the universe..

Your statement is in line with this kind of thinking..
A2G
1.2 / 5 (18) Nov 11, 2010
I like the post by Decimatus...I Agree that there is far too many statements made by self appointed experts that are in fact wild speculation...But wild speculation doesn't bring more funding. Look at how many times the "experts" are surprised by a new finding..Surprise indicates lack of true knowledge...If you understand things then you are not "surprised2 in your field of study.. There needs to be more honesty in the papers being published today, but again you gotta look smart to keep the funding..You can't act like you don't really know..

Don't get me wrong, I love all the research and HARD data being collected at all levels. It's the wild speculation presented as fact that concerns me..If you accept wild speculation as fact it then keeps you from BEING OPEN to the real truth.

Remember the old t-shirt "Question Authority" I like that..OR would you rather believe that there are WMDs in Iraq. Just because someone is respected, in power, or has a PHD, doesn't mean they are right
Skeptic_Heretic
not rated yet Nov 11, 2010
Not necessarily. The color of stars and the metals content do not directly correlate. The color of stars is directly related to its mass.
Not really. The color of stars is related to multiple aspects. Mass comes in to it only in the rate of energy release. The higher the mass the greater the energy release, the whiter the color of the electromagnetic energy within the visible spectrum.

However, don't disregard the average galactic spectrum. When you see a galaxy that is redder in color (after correction for doppler effect) one can infer that the galaxy is older as there are fewer main sequence stars providing a variance in the spectrum of light. The more red a galaxy is, the more red giants and brown dwarf stars contained within, again, after correction for doppler effect. This results in higher potential metalicity due to the fairly established rate of stellar nucleosynthesis from the standard stellar sequence model.
Au-Pu
not rated yet Nov 12, 2010
Thank you Skeptic Heretic
I hope A2G gets help and recovers.
The work would have been more complete if it had estimated the approximates ages of the galaxies in their study.
As presented it appears to be a fairly superficial study, lacking depth in many areas.
Perhaps they will do some follow-up work and fill those gaps?