By Dwayne O'Brien

Published: September 25, 2008

O ne glance at the cork board in Julia Velkovska's office and you get a good idea of what makes her tick. Push pins hold photos of family, posters of physics seminars past and future, and graphics from research collaborations. And there, a few push pins away in the upper corner: a photo of her scaling a near-vertical cliff face, her smallish frame barely visible save for the sure hands, red helmet and huge grin.

As an associate professor of physics and astronomy at Vanderbilt University, Velkovska enjoys introducing students to the fundamentals of physics as much as she does carrying on cutting-edge research on the properties of exotic states of matter that haven't existed since the Big Bang. She is also a wife, a dedicated mother of three boys and passionate about rock climbing — a sport that, much like physics, makes her proud of her accomplishments but always looking for the next mountain.

Velkovska grew up in Burgas, the fifth largest city in Bulgaria, located on the coast of the Black Sea. Even early on she was curious about the world around her. "When I was little, I liked to take things apart to see what was inside,” she says. It seems she also had a knack for building things. "When I was in the third or fourth grade, we had a construction club and we played with construction toys. There were about twenty boys in the club and I was the only girl. But when we would have a speed competition to build an object with construction toys, I always came in first,” she says with a smile.

Julia's interest in physics began in the seventh grade. "I had a very good physics teacher,” she says. "He spent a lot of time with us and showed us interesting things — not only in the classroom but on field trips to see what physicists were doing in real life. That was something that was very appealing to me.”

Being a physicist was not a family tradition: Julia's father was an engineer and her mother an accountant. It was her father who steered her toward majoring in what was called engineering physics at Sofia University "St. Kliment Ohridski” in Sofia, Bulgaria, where she went on to earn her master's degree in 1988.

In Sofia, Julia met theoretical physicist Momchil Velkovsky and the couple were married in January 1990. At that time, Bulgaria was in a difficult political and economic transition from communism to a free-market society. Funding for scientific research was scarce. Knowing that they wanted to pursue careers in physics and seeing much better opportunities elsewhere, the couple came to the United States in 1991, where both studied at the State University of New York (SUNY) at Stony Brook. Julia earned her Ph.D. in 1997, continued as a post doctoral fellow at SUNY until 2000, then became an assistant physicist at Brookhaven National Laboratory in 2001. She joined the Vanderbilt faculty in 2003. Momchil is a research physicist at Vanderbilt as well.

Velkovska's current research explores the nature and properties of a state of matter that hasn't existed since the very earliest moments of the universe. Dubbed the quark-gluon plasma, it is created fleetingly in the near speed-of-light collisions of heavy ions like gold nuclei in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab. These extremely violent collisions literally melt the protons and neutrons of the nucleus into their component parts: quarks and gluons. These particles never exist alone — only bound in pairs or in triplets to make protons and neutrons. As the plasma expands and cools, the quarks and gluons recombine into the larger and more familiar particles within milliseconds of the collision. "In a way,” Velkovska says, "a heavy ion collision replays the evolution of the universe. Like the early universe, it was very hot in the beginning and cooled during expansion. As it cooled, matter came out the way that it is now — no quarks and gluons; everything is bound in protons and neutrons.”

Velkovska and her Vanderbilt colleagues were part of a PHENIX collaboration that established that the quark-gluon plasma actually behaves more like a liquid than like a gas, as was previously thought. The next step was to determine whether the plasma had achieved the thermal equilibrium necessary to define it as a state of matter. To determine that would require an upgrade to a detector in the PHENIX experiment.

Julia convinced her PHENIX collaborators that her design was worth investing a million dollars to build and install. Then she built the panels with the help of her post doctoral students in a clean room in the physics building on the Vanderbilt campus.

The time-of-flight detector identifies the particles that are produced by the plasma as they ionize gas that is injected between two panes of glass. The detector's main components are surprisingly commonplace: plate glass and fishing line. "Yes, ordinary fishing line that I got from Bass Pro Shop,” Velkovska says. "Because you want to measure times very precisely, you need very small gaps and you need them to be very uniform. It turns out that ordinary fishing line has very good properties: it's very uniform, incompressible. So if you want to put half a millimeter thick sheets of glass on top of each other and you want to have 230 microns spacing between them, it's very easy to do it with fishing line. We put glass, fishing line, glass, fishing line. So the materials apart from the electronics were very cheap. Nevertheless, we have twice the timing resolution with our detector than what you could get with older, much more expensive detectors based on scintillators.”

A project of this scale usually takes years to build; Velkovska's team of post docs, grad students and undergrads did it in relatively short order. "In 2004, we built the first prototypes and tested them in Japan,” Velkovska says. "In 2006, we installed the completed detector and the electronics, and in 2007 we took the first data. It was a wonderful opportunity to get a lot of students involved here at Vanderbilt.” Due in large part to the data collected from this detector, her team established that the quark-gluon plasma has indeed achieved thermal equilibrium, though the exact mechanism behind it is still a mystery.

Julia enjoys working with students and finds teaching both challenging and rewarding. "The reason I became a physicist was because of my first physics teacher,” she says. "If I can influence just a few of my students to do the same, then it's very rewarding.” She has already had several students come through her introductory course and decided to become physics majors afterwards. "In fact, for one of them, I just wrote a recommendation for graduate school,” she says proudly.

While at the University of Sofia, Julia was introduced to two loves of her life. She met Momchil, and he took her rock climbing. She fell for both. Since then, the couple have been climbing all over the world. "We have been to the Rockies, and I've climbed in the Alps as well.” They enjoy the thrill and challenge of the higher mountains. "We've been to some very high peaks. The highest is 5000 meters in Tajikistan. The name of the peak if I translate it from the Russian name is 'Castle,'” she says. The couple have also climbed Longs Peak, the highest mountain in the Rocky Mountain National Park.

Julia finds ways to combine her work and her passion. She organizes conferences at which the participants talk about physics issues in locations where she also gets to go rock climbing with the students. "A couple of years ago we held it in Sardinia: there were some very nice rocks there. This year we're going to Estes Park [Colorado],” she says.

The couple have three sons: an older brother and fraternal twins. Stoycho is 17 and entering Cornell to study biology with an eye toward becoming a medical doctor. "He likes physics but was inspired by his biology teacher,” Velkovska says. The 12-year-old twins, Pavel and Ivan, have very different personalitites, but both play chess competitively; their school chess team recently won the Tennessee state championship. Stoycho has taken up climbing as have Pavel and Ivan, though the twins climb mostly indoors on climbing walls.

Velkovska will continue taking data from the PHENIX detector to study the nature and behavior of the quark-gluon plasma. The next project that she's getting involved with is an experiment at the large hadron collider located on the Franco-Swiss border near Geneva. "I'm spending my sabbatical year [there] and will be going there with the family this fall,” Velkovska says.

Undoubtedly, many more items are destined for the cork board as Julia looks for the next question to answer, the next instrument to build, and the next mountain to climb.