Twisted galaxies offer look at early universe

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If each galaxy were an island consisting of just the visible material, galaxies would glide past each other in the vastness of space with only the mildest gravitational tug between them. (NASA PHOTO)

If galaxies formed near the beginning of time, why are there galaxies with spectacularly peculiar shapes?

Galaxies, once called "island universes," are vast collections of stars and gas bound together by the compelling force of gravity. After all these billions of years, wouldn't gravity cause all the stars to settle into uniform orbits, ensuring all galaxies had regular shapes? Why are there distorted galaxies like those in the colour image released by NASA on Feb. 18, 2010?

The orange, normal spiral galaxies are shaped like Frisbees, in contrast to the sweeping colourful, distorted wreck prominent in this view, which I created as a participant in a research project led by Sarah Gallagher at the University of Western Ontario.

At the University of Manitoba, I study the origin of distorted galaxies by examining the flow of gas in both peculiar galaxies and regular spiral galaxies. My colleague Jason Fiege and I create models and acquire observations with mainly Australian colleagues.

My NASA image zooms in on Hickson Compact Group 31 (HCG 31), a rare example of four tiny galaxies in such close proximity that they would all fit within our own Milky Way Galaxy.

The discovery that 90 per cent of the material in regular-shaped galaxies can't be seen by telescope first illuminated why peculiar galaxies exist. This so-called dark matter consists of everything from black holes to exotic subatomic particles such as neutrinos. However, it seems that at least 50 per cent of dark matter is still unaccounted for, spurring on nuclear physicists to hunt for as yet unobserved exotica using particle accelerators or underground detectors such as Canada's Sudbury Neutrino Observatory.

Regardless of the form this mysterious matter takes, it is the enormous quantity and far-reaching volume associated with an individual galaxy that accounts for the peculiar shapes of some galaxies. If each galaxy were an island consisting of just the visible material, galaxies would glide past each other in the vastness of space with only the mildest gravitational tug between them.

The surprise is that we observe an impressive gravitational impact. This is because each island universe is floating in its own private sea of dark matter.

Stars and gas are gravitationally wrenched out of each galaxy like taffy, forming long tails such as the blueish strand stretching across HCG 31.

As time progresses, the tiny galaxies merge into a single gasless, elliptical-shaped galaxy and the gravity of this newborn wraps its tails around itself.

HCG 31 is relatively nearby, only 166 million light-years away, allowing us to study in up-close detail the fireworks caused as the gravitationally mangled gas is crushed and converted into hot stars.

The data that I used to construct this image come from NASA's Hubble Space Telescope (HST), Spitzer Space Telescope (SST), and Galaxy Evolution Explorer (GALEX).

The sharp images from HST allowed our team, led by Gallagher, to determine that very young star clusters, less than a few hundred million years old, are spread throughout HCG 31. The long blue tail does not contain old stars, demonstrating that this is the first gravitational encounter between the four galaxies.

Therefore, HCG 31 provides a rare surrogate for studying encounters between galaxies when the universe was young. HCG 31's elegantly peculiar galaxies will merge into a single normal elliptical galaxy within a billion years or so. Ellipticals could have formed this quickly in the universe's youth, explaining why many have roughly the same age as our 13-billion-year existence.

Jayanne English is an associate professor in the department of physics and astronomy at the University of Manitoba.

The Learning Curve is an occasional column written by local academics who are experts in their fields. It is open to any educator from Winnipeg's post-secondary institutions. Send 600-word submissions and a mini-bio to thelearningcurve@freepress.mb.ca.

Learning Curve

Jayanne English

Associate professor;

Department of Physics

and Astronomy; U of M

Republished from the Winnipeg Free Press print edition May 25, 2010 B5