Jan. 25, 2013 – A paper co-authored by James Lombardi, an associate professor of physics at Allegheny College, appears in the January 25th issue of Science magazine. “Identification of the Long-Sought Common-Envelope Events” investigates how the brightness and color of two merging stars change as the stars become one. The research was done in collaboration with Natasha Ivanova (University of Alberta), Stephen Justham (Chinese Academy of Sciences) and José Avendaño Nandez (University of Alberta).
Stellar outbursts used to be lumped into two categories: novae or supernovae. But over the years researchers have recognized another class of outbursts with luminosities between those of novae and supernovae, called intermediate-luminosity red transients or ILRTs.
Ivanova, Justham, Nandez and Lombardi suggest that these ILRTs are actually the signatures of phenomena known as common-envelope events, which have only been theorized but never observed directly. Such common-envelope events are proposed to occur when two stars temporarily orbit within a shared stellar envelope. The star with lower mass should become engulfed by matter that is transferred to it from the larger and more evolved companion star, according to theory. And researchers believe that such events form a wide range of close binary systems, such as X-ray binaries and double-neutron stars.
Lombardi and his colleagues have now modeled the properties of ILRTs and found that the time scales, energies, colors and ejection velocities of these events agree with the predicted properties of common-envelope events. Based on their model, the researchers suggest that many ILRTs result from common-envelope events and that ILRTs represent their long-sought signatures.
One of the world’s most respected scientific journals, Science accepts less than 7 percent of the manuscripts submitted.
Lombardi has taught at Allegheny College since 2006. He earned an A.B. degree from Princeton University and an M.S. and Ph.D. from Cornell University.
Photo: A snapshot from a computer simulation of two stars shortly after they have merged. The image spans a distance of more than 2000 times the radius of our Sun, and the colors show how the mass of the two stars is distributed. The stars merged in the central white region, and the surrounding colors show a clumpy envelope of material that has been launched outward. The gigantic size of the envelope is largely responsible for the outburst in brightness following a merger.