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The National Aeronautics and Space Administration has awarded a grant and satellite time to Michael Stark, assistant professor of physics, to study the highly energetic interaction between two orbiting starsin a binary system designated SAX J2103.5+4545.
Stark is working with physics majors Carolyn Heffner ’06 (Cleona, Pa.) and Michael Kaczmarczik ’06 (Elkins Park, Pa.) — who also is pursuing an A.B. degree with a philosophy major — to collect information from an x-ray binary star system, convert it into a useful form, and analyze the results. The information is received from NASA’s Rossi X-ray Timing Explorer, launched in 1995 to study the rapid changes in stars that emit X-rays.
The grant is allowing Stark and his students to explore basic physics conceptsunder conditions that could never be simulated on earth, he says. They will present their research in January at the American Astronomical Society conference in San Diego, Calif., and submit a paper for publication by a scientific journal.
The astrophysics is in collaboration with scientists at the Goddard Space Flight Center in Maryland, and Starkand his students often travel thereto work with other astrophysicists. Eventually, the students may build on the experience and conduct yearlong, independent honors research projects next year.
Stark credits the high quality of Lafayette students for making it possible to carry out his research objectives.
“My colleagues at universities and government research labs work with graduate and post-doctoral students. I am able to carry out the same kind of research at Lafayette because of the high quality of students and because I have the opportunity to work closely with them,” he says.
Stark mentors students in honors thesis projects and collaborates with them through Lafayette’s EXCEL Scholars program, in which students conduct research with faculty while earning a stipend. The program has helped to make Lafayette a national leader in undergraduate research. Many of the more than 160 students who participate each year share their work through articles in academic journals and/or conference presentations.
“The quality of students at Lafayette is very high and I have had no trouble finding students to work on EXCEL projects with,” he says. “In fact, I had to turn several students away from my researchThe students I have worked with have been curious and interested in the exploration that is part of fundamental scientific research.”
Thus far, the three researchers have counted the number of revolutions the binary system’s pulsar – the magnetized neutron star – makes over a three-yearperiod and created an orbital model for the star system. An accurate orbital model allows them to study the interaction between the two stars in precise detail.
A major goal is to understand how the pulsar produces X-rays and how this production changes as the star gets brighter and fainter, says Stark.
“I think it’s exciting to be able to study an object that’s so far away from us in such great detail,” says Heffner. “This x-ray binary has some unique properties that will be fun to explore in detail.”
The star system is located about seven degrees northeast of the bright star Deneb in the constellation Cygnus. Such systems contain accretion-fed X-ray pulsars, meaning that the binary system consists of a highly magnetized neutron star – one that is extremely dense – and a more typical companion star.
The companion is losing material that becomes very hot as it falls onto the surface of the neutron star, Stark explains. Guided by the neutron star’s magnetic field, the material makes two hot spots on that star’s surface. As the star rotates, these spots appear and disappear, making the star seem to pulse. The spots are so hot that they emit X-rays, which don’t penetrate the Earth’s atmosphere and thereforecan only be observed by satellites.
“The material falling on the neutron star also makes it spin faster in much the same way that an ice skater spins faster as he pulls his arms in toward his chest, or the way a hurricane spins fastest near its center,” says Stark.
The relationship between the amount of material falling on the neutron star from the companion and the change in spin rate is the focus of his research. The star that Stark is observing is a transient source, meaning that it isn’t always visible. The amount of material falling from the companion star onto the neutron star determines its visibility.
Stark is collecting data from the binary system when the star is barely visible. This indicates that the rate of falling material is low, a state in which its relationship to changes in rotation is least studied and understood.
“The way material falls on the star neutron is actually quite complicated,” says Stark. “The material comes off the companion star in a stream of gas. This gas forms a disk around the neutron star reminiscent of the rings of Saturn. Gas flows through the disk toward the center until it encounters the star’s magnetic field. The material follows the magnetic field to two spots on the surface of the star, the magnetic poles. The part of this process we are getting at with this research is the interaction between the accretion disk (falling material) and the magnetic field. The small changes we observe in the rotation of the star, compared with the changes in the X-ray emission of the star, tell us about this interaction.”
Stark also conducted EXCEL Scholars research with physics major Malinda Saia ’04 (Turnersville, N.J.), who published her findings in Astrophysical Journal and presented them at the 201st meeting of the American Astronomical Society in Seattle. Saia studied a binary star system known as Cygnus X-3 to determine if the system is a neutron star or black hole, then conducted independent astrophysics research in a yearlong honors thesis during her senior year. Saia earned honors in physics and was a member of Sigma Xi, the international honor society for science and engineering research; Pi Mu Epsilon, the national mathematics honor society; and Sigma Pi Sigma, the national physics honor society.
Heffner believes her research with Stark lends her keen insight into the professional world by allowing her an opportunity to experience the type of work an astrophysicist does.
“It gives me the opportunity to take the information I learn in my classes and apply it to real situations,” she says. “Lafayette is a good environment for this type of work. It allows me to pursue my interests and gives me the opportunity to work with Professor Stark on this research project.”
“I like how you can work closely with the professors at Lafayette,” says Kaczmarczik. “Going into this research, I knew nothing but the very basics of astronomy and how research is actually conducted. Professor Stark has shown me how such research is carried out, as well as given me a better understanding of astronomy in general.”
“Physics has always interested me. It seems to encourage a broader understanding of not only the world, but the universe, which is appealing,” Kaczmarczik adds. “This project has given me a basis of understanding about astronomy research. Not only will this help in gaining admittance to a graduate school, it will also help me decide exactly what I want to study in the future.”
Heffner credits Stark for having “greatly influenced my education here by convincing me to major in physics, by offering me this research opportunity, and by being supportive and encouraging throughout the semesters.”
“I plan on attending graduate school and I think that being involved in undergraduate research will better prepare me for it,” she says. “Many students never get this opportunity until graduate school, so I’m happy to be able to start graduate school with experience.”
Stark’s prior positions include research associate appointments at NASA’s Laboratory for High Energy Astrophysics and its Goddard Space Flight Center. He also has been a faculty member at the University of Maryland, Denison University, and Marietta College.
Stark has contributed numerous articles to The Astrophysical Journal and has been published in other scientific journals, such as Physical Review Letters, Nuclear Instruments and Methods in Physics Research, and Physical Review. He is a member of the American Astronomical Society, High Energy Astrophysics Division.
He holds a Ph.D. in physics from University of Maryland and a B.S. in physics from Harvey Mudd College.
Kaczmarczik is president of the Outdoors Club, a board member of Lafayette Environmental Awareness and Protection, and a member of CHILL (Creating a Healthy, Interesting, Livable Lafayette) and the Chi Phi fraternity.
Heffner is a member of the Physics Club and Soccer Club.