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Answers in Galaxies Far, Far Away

What could be more exacting than a search for a needle in a haystack? How about a search for a single, faint star trail – millions of light-years from earth – in a boundless universe brimming with stars?

For two and a half years, Dr. Elizabeth Wehner, assistant professor in St. Thomas’ Physics Department, and a small, revolving group of undergraduate physics students (and one English major) have been doing just that.

This year sophomore Maria McQuillan and junior Nick Sinn have joined forces with Wehner to scrutinize images of far-away galaxies taken on a .9 meter telescope housed at Kitt Peak Observatory in Arizona.

The trio is analyzing tidal debris – streams of stray, mostly young, stars and gas clouds that shoot out from the core of their main galaxy – in one galaxy and one galaxy cluster.

“This research isn’t going to change the technology of day-to-day life. It’s more about answering big questions, like ‘How do galaxies form?’ ‘Did they change?’ ‘How and why did they change?'” and delving into the mysteries of the universe that bore us, Wehner said.

The galaxy at the heart of her ongoing Kitt Peak project is NGC3310, which Wehner has been studying for a decade. Its name refers to its placement as the 3,310th object in the New General Catalog, an astronomical catalog of star clusters, nebulae and galaxies in the universe. This past summer McQuillan (whom Wehner tasked to analyze images of the galaxy taken last spring) and Wehner made a significant find: a previously undiscovered stream of tidal debris, which compelled Wehner to make NGC3310 the focal point of her project. This year both will continue to analyze the “new” debris.

Sinn, who began working with Wehner last spring, is studying evolutionary patterns in a cluster of galaxies, collectively named HGC44, which means it’s the 44th cluster (of around 100) in the Hickson Compact Group, named after Paul Hickson, the first astronomer to catalog clusters of interacting galaxies. It’s part of an extensive (and also Kitt Peak-related) project for which Wehner is collecting data from other clusters and comparing them.

A brief lesson in colliding galaxies

Galaxies are a lot like dancers in a never-ending dance-a-thon. They’re constantly rotating and moving, and occasionally they bump into each other. One couple might waltz gracefully across the dance floor, remaining happily together the entire evening. While a persistent gentleman might step into the middle of another couple’s dance, shucking the other gentleman who, in turn, lags off to the side.

Galactic collisions can last for millions, even billions, of years – stars and gas clouds continually being plucked from the galaxy with the weaker gravitational force and new stars being born in the resulting streams of tidal debris – only ending when the galaxies merge into one or move out of each other’s orbit.

Dr. Elizabeth Wehner

Perhaps this is why all collisions also are commonly referred to as “interactions,” a gentler term that lends their gravitational tug-o-war meetings with the air of something not as violent.

Collisions between galaxies are vastly different from collisions on earth. When galaxies collide, they are not obliterated in a similar fashion to two cars smashing into each other head on.

When interacting spiral galaxies (like ours, the Milky Way) come to a rest, they often merge into one elliptical shape, “which is more of a squashed spherical shape versus a flat, two-dimensional disc like ours,” Wehner said.

“Stars are really tiny compared to how far apart they actually are from each other. There’s so much empty space between them that when galaxies collide, it’s about forming patterns of stars versus stars smashing into each other,” she noted.

McQuillan added this mind-blowing concept: “Galaxies can actually pass through each other almost, especially if they’re the same size, because they have similar gravitational forces.”

Sinn also was taken aback by what he’s learned. “Looking at galaxies and how they interact with each other is not what you’d expect,” he said. “You think, ‘Huge thing meets another huge thing equals one even huger thing,’ but it’s not like that. That’s what I love about physics. You look at one thing you’ve figured out about one little part of the universe and how it should be acting based on your models, and it doesn’t behave that way. Then you have to ask ‘Why?’ and figure it out.”

Thrown for a loop, happily

Clutching her heart, Wehner gushed: “NGC3310 is my favorite galaxy. I just feel drawn to it.” She even had a coffee mug made with the galaxy’s Hubble image emblazoned on it. The galaxy was one of the darlings of her Ph.D. thesis at the University of Wisconsin – Madison.

“NGC3310 is attractive to study because it’s close by, relatively speaking, and it’s face on (or perpendicular) to us. So instead of looking at it from the side, we can see the entire galaxy from our perspective,” she said.

To elaborate, she pointed to a cluster of blue and white clumps on the image of the galaxy on her computer monitor and described the scene: “You can tell that this is a starburst galaxy because it’s forming a lot of new (blue) stars.” Then her eyes widened. “Something has caused this galaxy to suddenly ignite in star formation. It doesn’t happen all by itself but you can’t immediately see the cause.”

It was hard not to feel excited with her when she added, “It takes awhile to figure out why it’s doing that.”

“Honestly, part of the motivation to photograph it again this past spring was that the .9-meter telescope we’re using just got a new instrument. I wanted to test it by taking some really deep images of NGC3310 to see if it’d pick up even more of the faint debris streams that I already photographed,” Wehner said.

At first, Wehner asked McQuillan simply to compile data from reduced images of the galaxy she’d previously taken. Then she was going to have her work on a different galaxy. That is, until they made an unexpected discovery: another “tidal loop” (of star debris).

Wehner and her colleagues at Madison had found several tidal loops in their research around 10 years ago, but not this one.

With the discovery, the instrument proved it was at least as good as its predecessor.

“This loop was more prevalent in these new, deeper space images,” McQuillan said. “That was cool to see … this circle of debris going out and coming back around into the galaxy. Elizabeth said it had been in a previous collision with a smaller galaxy, and NGC3310 was so big that it just sort of ate it up. The small galaxy got caught inside and ripped apart in its orbit, so all of these tidal loops are the remnants of this little galaxy that are just circling around.”

It’s painstakingly difficult to spot the new streak of tidal debris on the image with the naked eye. It only becomes clear after mathematical measurements of the stream’s color and other properties are taken. Old stars are red, while newer stars – which tend to be born in tidal debris – are blue.

McQuillan will continue to study the newfound loop this year and see the analysis through to publication with Wehner.

Wehner noted that previous studies on the galaxy have paid most attention to the starburst in the middle. “I’m probably the main person who studies the tidal debris,” she said.

Answers to big questions

NGC3310 is 50 million light-years from earth; the four galaxies that make up HCG44, 59 million. Why study galaxies far, far away from us?

Among the biggest reasons is to discover what could happen to our own galaxy, the Milky Way, which is on a collision course with the galaxy Andromeda. A “mere” 2.5 million light-years from us, it is the closest spiral galaxy to us, and more massive. Analysis of other galaxies helps scientists decipher how the collision process works.

“That’s something we’re working on,” Wehner said. “One thing I’m interested in doing with NGC3310 is to compare the tidal debris with models for our own galaxy. We have streams of tidal debris around our galaxy so things are colliding with us as we speak. This is a way of looking outwardly and seeing that in another system. It can be really hard to see around our own galaxy because if there’s a tidal stream up in the night sky, how do we pick that out from the stars in our own galaxy? It’s hard to see and, therefore, measure it. We can look at other systems and try to understand better what’s going to happen to our galaxy.”

No need to panic or hasten our plans for developing warp speed to bust us out of the Milky Way. Our destined smash-up won’t occur for another four billion years.

Onward

McQuillan and Sinn worked 40 hours per week this past summer, thanks to funding from a Minnesota Space Consortium Grant and Physics Department start-up funds allocated to Wehner’s Kitt Peak project, which she negotiated upon her hire. The start-up funds were used to buy into the .9 meter consortium, which entitles Wehner to yearly three-day usage of the Kitt Peak telescope.

Up until now, the pair have studied images taken at the observatory by Wehner and their predecessors, fellow St. Thomas students Marissa Beckers, Rachel Busse (the lone English major), Katrina Korman and Sarah Millholland. But this spring, the pair finally will be able to see the “stars” of their labors up close and personal when they accompany Wehner on her annual date with the telescope.