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Researchers Study X-ray Binary Stars in Nearby Galaxy

Laycock Gets $57K Grant

Silas Laycock
Silas Laycock in front of the 8-meter Gemini North telescope on the summit of Mauna Kea in Hawaii.


Edwin L. Aguirre

Black holes. Neutron stars. White dwarfs. Galactic cannibals.

These are just some of the exotic cosmic beasts that Silas Laycock has been studying professionally since he obtained his Ph.D. in astronomy from the University of Southampton in England in 2002.

Laycock, who joined UMass Lowell’s Physics Department faculty last year, has worked at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, and the Gemini Observatory on Hawaii’s Big Island. He has also used some of the world’s largest telescopes, including NASA’s orbiting Hubble Space Telescope and Chandra X-ray Observatory.

Recently, he and his team of researchers from the University of Washington, CfA and NASA were awarded a two-year $56,707 grant by the Smithsonian Astrophysical Observatory to study X-ray binary star systems in IC 10, a dwarf irregular galaxy 2.2 million light-years away in the constellation Cassiopeia.

“Our year-long observations using the Chandra and Gemini telescopes were completed in late 2010,” says Laycock, who is the project’s principal investigator. “The grant money is being used to set up a computer lab for analyzing the data and hire a student assistant.”

He and his graduate student, Andrew Balchunas, are currently working on two journal articles based on the research — one was presented by Laycock as a poster during the American Astronomical Society (AAS) meeting in May in Boston and the other will be presented by Balchunas at the AAS High-Energy Astrophysics Division meeting this September in Newport, R.I.

A New Astrophysical Laboratory

X-ray binary stars (XRBs) consist of a compact, ultra-dense object, such as a neutron star, that is closely orbited by a hot, massive companion star. The neutron star’s powerful gravity captures some of the gases flowing away from its companion, forming an “accretion disk” around the neutron star. As these captured gases spiral down and fall onto the surface of the neutron star, they get heated up and give off powerful X-rays.

“XRBs are sensitive probes of massive-star evolution,” says Laycock. “Accretion-powered binaries containing black holes and neutron stars are the relics of the most massive and short-lived stars that have ever formed. These systems are visible in X-rays over cosmological distances and efficiently provide fundamental astrophysical parameters — for example, orbital periods, spin, mass, mass-transfer rate, age, magnetic field, etc. — that are unobtainable at other wavelengths.”

Using their observations as well as archival data, Laycock and his team are looking at IC 10 as a kind of new laboratory for astrophysics. They are investigating the role of age and environment on massive stars and their relics by studying the population of transient XRBs in such a young, nearby star-forming galaxy. They are also conducting spectroscopic and timing studies of the supermassive black-hole binary system, called IC 10 X-1, lurking deep in the heart of the galaxy.

“IC 10 X-1 is the most massive, dynamically confirmed ‘stellar’ black hole known, with a mass 24 times that of the sun,” he says. “We want to find out whether the black hole has an accretion disk, as well as search for evidence of past activity.”

This artist’s illustration of an X-ray black-hole binary shows material from a blue supergiant star being sucked into the accretion disk surrounding a massive black hole.