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University of Michigan astronomers examined old galaxies and were surprised to discover that they are still making new stars. The results provide insights into how galaxies evolve with time.

Dead Galaxy? Don’t Think So.

30 May , 2011

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There was a time when most astronomers concluded that elliptical galaxies were a lot like their globular clusters – full of similarly evolved and aged stars. But not anymore. Thanks to the resolving power of the Hubble Space Telescope, a team of researchers from the University of Michigan were able to peer into the heart of Messier 105 and pick out several young stars and clusters. Apparently, “The reports of my death have been greatly exaggerated…”

U-M research fellow Alyson Ford and astronomy professor Joel Bregman are scheduled to present their findings May 31 at a meeting of the Canadian Astronomical Society in London, Ontario. Using the Wide Field Camera 3 on the Hubble Space Telescope, they saw individual young stars and star clusters in four galaxies that are about 40 million light-years away. One light-year is about 5.9 trillion miles.

“Scientists thought these were dead galaxies that had finished making stars a long time ago,” Ford said. “But we’ve shown that they are still alive and are forming stars at a fairly low level.”

We’re all aware of differing galaxy structures, from grand design spirals to disturbed irregulars. However, perhaps one of the most common is the elliptical. Ranging in flat form to nearly spherical, these smooth customers can contain anywhere from hundreds of millions to over one trillion stars – and most of them are believed to be the offspring of galaxy collision. Most elliptical galaxies are composed of older, low-mass stars, with a sparse interstellar medium and minimal star formation activity. Making up somewhere between 10 to 15% of known galaxy population, they are surrounded by globular clusters and usually make their home at the center of galaxy clusters. But what elliptical galaxies aren’t known for is star formation.

“Astronomers previously studied star formation by looking at all of the light from an elliptical galaxy at once, because we usually can’t see individual stars. Our trick is to make sensitive ultraviolet images with the Hubble Space Telescope, which allows us to see individual stars.” said Ford. “”We were confused by some of the colors of objects in our images until we realized that they must be star clusters, so most of the star formation happens in associations.”

The eureka moment came when the team turned the Hubble towards a galaxy most of us have observed on a personal level – M105. Located 38 million light years away in the constellation of Leo and part of the M96 Galaxy Group, this rather ordinary looking elliptical galaxy is one of the brightest to observe. Although there wasn’t any reason to believe star formation was in progress, Ford and Bregman saw a few bright, very blue stars, resembling a single star 10 to 20 times the mass of the Sun. In addition, they also observed objects that aren’t blue enough to be single stars, but instead are clusters of many stars. When accounting for these clusters, stars are forming in Messier 105 at an average rate of one Sun every 10,000 years, Ford and Bregman concluded. “This is not just a burst of star formation but a continuous process,” Ford said.

New stars from a dead galaxy? Maybe it’s a zombie. And it’s not the first time the Hubble has looked its way, either. Investigations of the central region of M105 have revealed that this galaxy contains a massive central object of about 50 million solar masses – a supermassive black hole. Of course, this new evidence creates more questions than it answers and high among the ranks is the origin of the gas that forms the stars.

“We’re at the beginning of a new line of research, which is very exciting, but at times confusing,” Bregman said. “We hope to follow up this discovery with new observations that will really give us insight into the process of star formation in these ‘dead’ galaxies.”

Dead… But maybe not so dead, after all.

Original story source Physorg.com.


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Ivan3man_At_Large
Member
Ivan3man_At_Large
May 30, 2011 8:49 PM

There was a time when most astronomers believed…

Hold it right there! Most astronomers, like most good scientists, believe nothing; instead, they hypothesize, conclude, contemplate, conjecture, consider, deliberate, estimate, infer, postulate, speculate, or understand, but not bloody “believe”.

Richard Kirk
Guest
May 31, 2011 12:05 PM
I applaud the sentiment, but… There are at least two popular interpretations of the word ‘believe’. Many words in English are ambiguous, and we resolve ambiguities by looking at context. Here in a scientific community, we are likely to mean ‘well, I think this is more probable than the alternatives I know about, and I am likely to continue to do so until better evidence comes along’ rather than ‘Credo! It Is Written! All unbelievers should be purged with Holy Fire!’ Leastways, that is what works for me in the UK. Readers from other countries may use the word differently. I don’t want to make Tammy’s job any harder then it is already, but ‘conclude’ also sounds like… Read more »
Ivan3man_At_Large
Member
Ivan3man_At_Large
May 31, 2011 9:08 PM

Many words in English are ambiguous, and we resolve ambiguities by looking at context.

Well, in this context, since you’re making a comparative statement, “I don’t want to make Tammy’s job any harder then it is already,…”, it should be than, not “then”. So there!

Richard Kirk
Guest
June 1, 2011 12:55 PM

Well, waddya know, he’s right too.

Bah.

Anonymous
Guest
Anonymous
May 30, 2011 11:13 PM

Extremely interesting find. We know that ellipticals do have some gas floating around, but to know how that then goes on to form young stars is a very interesting question!

Lawrence B. Crowell
Member
Lawrence B. Crowell
May 31, 2011 2:31 AM

I find it odd that elliptical galaxies were thought to be dead. In fact as I understand the Milky Way and Andromeda will merge into an elliptical galaxy and it is thought there will be a bit of star birth activity. I am not a galaxy evolution maven, but it is my understanding that elliptical galaxies do evolve into spiral galaxies.

Galaxies in this universe will continue to have decent stars for several 10s of billions of years. Stars will exist for a trillion years. By comparison galaxies like ours are pretty young as yet.

LC

DrFlimmer
Member
DrFlimmer
May 31, 2011 9:11 AM

Minor correction: Ellipticals do not evolve into spirals. That’s what Hubble thought, and why he arranged his “tuning fork” the way he did.
AFAIK, it’s the general agreement these days that it’s the other way around: flat spirals evolve (e.g. by mergers) into fat ellipticals (the whole universe is just too human… or is it the other way around? wink).

Lawrence B. Crowell
Member
Lawrence B. Crowell
May 31, 2011 11:22 AM
I thought much the same. The Hubble scheme was thought to not reflect an evolutionary process. Then a couple of years ago I remember reading, of course this does not count for much of a reference, there was evidence that elliptical galaxies did evolve into spirals. As I recall the argument is that density waves in rotating elliptical galaxies end up establishing spiral structure. This does presume elliptical galaxies have a net angular momentum of rotation, which makes some sense. So now my sense is a big “I dunno.” I must confess I have always thought it mysterious that galaxies have this well ordered disk-spiral structure. It would not seem unreasonable that a rotating blob of stars numbering… Read more »
Al Wilson
Guest
Al Wilson
May 31, 2011 1:46 PM

Spirals are considered to be low entropy systems, and ellipticals are high systems.

The gas likely comes from the IGM, or via absorption of a gas-rich dwarf galaxy.

Lawrence B. Crowell
Member
Lawrence B. Crowell
May 31, 2011 4:12 PM

Of course I am conjecturing, but I think low entropy state can be arrived at from a high entropy one. A high entropy system of particles has a higher temperature, but if it can evaporate off particles, thus increasing the entropy of its environment, so that it can cool to a lower entropy. Evaporative cooling does just this. So by throwing off material, gas maybe stars etc, into IGS the galaxy could enter into a lower entropy state. This might also involve the absorption of material by black holes, where the thermodynamics of black holes plays a role.

LC

Aqua4U
Member
May 31, 2011 1:13 AM

How does the rotation rate of the central black hole(s) influence a galaxy’s formation?

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
May 31, 2011 8:28 PM

Likely not at all. How would they couple?

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