Thread: Galactic Bars May Kill Spiral Galaxies... (from Science Daily)

ScienceDaily (Nov. 8, 2010) — With the help of the army of volunteers working on the Galaxy Zoo 2 'citizen science' project, an international team of scientists have discovered that the bars found in many spiral galaxies 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 our own 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 (as shown in the galaxy in the left hand side of the image). 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 us with a great puzzle because we still don't understand why some galaxies have bars and others do not.

The team, led by Dr Karen Masters of the Institute of Cosmology and Gravitation at the University of Portsmouth, drew on the work of the volunteers taking part in Galaxy Zoo 2, the follow on from the highly successful Galaxy Zoo 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 colours 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 colour.

The astronomers conclude that bars might help to kill spiral galaxies, although how they do it remains a mystery. But the Milky Way has a bar too, so this discovery may be telling us something about its future.

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 galaxies 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 or 'Zooites' share her enthusiasm. Eric Hobein adds "It's nice to figure out how we help and be a super-tiny part of it all"; whilst Mike Tracey comments "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."

For more information about the Galaxy Zoo project, visit: www.galaxyzoo.org

Hmm. That's very interesting. And, you know, you can already tell that our galaxy is becoming a red galaxy. For example, scientists have estimated that red dwarfs make up over 60% of all the stars in the galaxy!

It's interesting that you mention that, because a recent stellar survey I read about a year ago suggested that, rather than a ratio of large to small stars of 500 to 1, the actual ration might be 2,000 to 1. That's an interesting thought. This is partially why some astronomers are saying that the age of supernovae might be coming to an end. If there are well over 2,000 red dwarf stars in comparison to the larger, blue stars, this may well be true.

Wow. That has a lot of far-reaching consequences, too. If there aren't that many supernovae, then the hydrogen clouds which later form into stars would not be enriched with the materials to make plentiful planets like Earth (everything below iron on the periodic table, including gold, arsenic, and good old uranium). That could mean that planets would stop being formed that contained the elements fit for life. So, in a way, we're lucky to come just before that period!

No kidding. I mean, sure, type 1a supernovae will keep enriching these clouds as time goes on, but the nasty type 2 supernovae are becoming fewer and fewer. The astronomer Phil Plait actually said that "we exist in a season for life, if you will, in the Universe", and I suppose you could take that very seriously because there are only so many stars, and they can only burn for so long.

True, true. We are very lucky to have been created at such an early point. I really like Michio Kaku's ideas of how civilization could, eventually, travel to other Universes. I think it would be the greatest thing if we could. If we were not restricted to just one Universe, destined to be eradicated in a few trillion years. If we could travel between Universes, we could, in a way, break the Second Law of Thermodynamics - we could always have an almost infinite amount of resources and energy.