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Quasar Girl

Quasar Girl

Astronomy student Krista Smith fulfills her dream to become an astronomer and studies quasars, the massive, incredibly distant, extraordinarily bright galaxies with active black holes at their center.

krista.jpgThe earliest documentary evidence of Krista Smith’s love affair with the cosmos is a crayon drawing from third grade. Smith and her classmates were given a blank piece of paper and told by their teacher to draw themselves as they imagined they would be in thirty years. She drew a stick figure girl standing at a giant telescope under a field of green and red stars.

“I’ve known my whole life I wanted to do astronomy,” says Smith, who will graduate in December with a degree in astronomy. “I remember when we would go to the public library when I was young. My sisters would all be in the children’s section. I would head upstairs and to the left to the astronomy aisle. I couldn’t read most of the books all that well, but I would look at the pictures. I never stopped.”

Growing up in McKinney, Texas, Smith supplemented her library visits with whatever else she could find on the subject. She commandeered the family television on Tuesday nights, which was astronomy night on the Science Channel, so that she could watch the three one-hour documentaries that were broadcast. Through her school’s gifted and talented program, she was put in touch with a woman who used to work for NASA, who gave her the specific URLS of various astronomy-related sites (a valuable commodity in the pre-Google era). In high school, she joined the Academic Decathlon team only after she learned that the year’s theme would be astronomy. She ended up conducting a year-long seminar on the subject for her fellow decathletes.

By the time she arrived as a transfer student at The University of Texas at Austin, Smith was so eager to immerse herself in the subject that she enrolled directly in upper-level galactic physics, skipping the introductory astronomy lecture. She also managed to secure a place in the lab of astronomy professor Greg Shields.

“I’m not a shy person, and if there’s a way to cut out the bureaucracy I usually take it,” she says. “I got on the internet and emailed six professors, and said—alright, I’m an undergrad, and I have no lab skills, but I’m interested. I sent it out, and waited. A day later Dr. Shields wrote back, and said yeah, come by the office and we’ll discuss it. So I came by the day after I moved in, and two days later I was working.”

[pullquote]When the great spirals formed, out of the screaming brightness, in vibrant whorls of green and blue and red, my heart formed with them, rejoicing in the new breed of beauty. ... They resembled precious stones; deep emeralds, rich sapphires, and wine-colored rubies, cut in exotic and rare shapes. When I looked upon them from closer in, more wonders awaited me. —from “Genesis,” a short story by Krista Smith[/pullquote]

Smith’s research in Shields’ lab, where she’s been for the last two years, has become the center of her academic experience in Austin. She’s a named author on two papers from Shields’s lab that were published in The Astrophysical Journal, the premier astronomical research journal, and in April was the first author on another paper in the journal.

A Search for Binary Active Galactic Nuclei,” Smith’s paper, is the fruit of her eyeballing of more than 24,000 quasars from the Sloan Digital Sky Survey (SDSS), a multi-year survey that’s able to obtain spectrograpic data on objects as far as tens of billions of light years away.

Smith’s focus has been on quasars, which are massive, incredibly distant, extraordinarily bright galaxies with active black holes at their center.

“All galaxies, we believe, have black holes at the center,” says Smith, “but the difference is that the black holes in quasars are being fed huge quantities of gas and dust and matter. As this matter spirals in it gets so intensely heated that it becomes relativistic. Plasma jets start emitting. It’s unbelievably bright, which is why we’re able to see quasars from so far away.”

According to prevailing cosmological theory, says Smith, the early universe was full of galaxies crashing into each other and merging to form larger galaxies.  Gravitational forces at work during these mergers should have fed gas to the black holes in both galaxies, causing them to shine as close pairs of quasars.  Her hunt through the data from the SDSS has been for observational evidence of binary quasars in the process of merging.

“Theory predicts that between 15-20 percent of quasars should be binary,” says Smith. “Previous studies have found only 0.1 percent or so, which is not even close. But all of these other searches have been looking for these things optically. They’ve been looking for images with two sources of light. The problem with that, though, is that you’re necessarily restricting yourself to identifying early phases of the mergers, when the quasars are still far enough far apart that you can see them individually.”

Smith’s strategy, by contrast, involves looking not at the pictures but at graphs of the spectral emissions of quasars. In doing so, she‘s been able to identify many new binary quasar candidates by way of a telltale “double peak” in an area of the radiation spectrum where the active nuclei of quasars are known to emit.

“I went through about 24,000 of these quasar spectra, one at a time,” says Smith. “We found 1.8 percent that had these double peaks. It doesn’t sound like very much, but it’s an order of magnitude higher than anyone else had found, so that’s an immense improvement.”

Such double-peaks aren’t proof of binary quasars, cautions Smith. Other astronomers have suggested alternative explanations for the double peaks. The double-peaks are, however, a significant find. And Smith’s success in finding them—her ability to uncover meaningful patterns in the vast nebula of astronomical data—not only bodes well for her future as an astronomer, but suggests something about what kind of astronomer she will be.

“I think I’ve always been an observer and probably always will be,” says Smith, who plans to apply to doctoral programs in the fall. “I wasn’t one of those thoughtful children who sat there learning math and figuring things out in my head, like a theorist would have been. I was the kind of kid who saw the same constellation at home and at grandma’s house, which was a four hour drive away, and wondered how that could be. Everything else was different. The trees were different. The ground was different. The house was different, but these stars were still the same. I figured it out eventually, and it blew my mind. As I learned more and more, it took more and more to blow my mind, which is how it works for all of us, I suppose. It’s just gotten bigger and bigger from there.”

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Tuesday, 07 February 2023

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