Kastor Elected APS Fellow

The American Physical Society (APS) announced that David Kastor, a senior lecturer in physics, was recently elected as a fellow of the society based on the recommendation of its Topical Group on Gravitation. The group cited Kastor for his “influential work on a broad span of topics in gravitational physics ranging from the formal definition of conserved quantities in General Relativity through new exact black hole solutions all the way to brane architectures relevant for string theory.”

Kastor will receive a certificate at an APS meeting in Savannah, Ga. in April . His name will also be published in the March issue of APS News. “Election to APS Fellowship is recognition by your peers of your outstanding contributions to physics,” the organization points out.

Kastor, who has been at UMass Amherst since 1993,focuses his research on the theory of black holes in general relativity and related theories. As he explains, “Astronomers are interested in black holes because, somewhat ironically, they are amongst the brightest objects in the sky. Although light cannot emerge from a black hole, matter falling into the deep gravitational well of a black hole emits highly energetic radiation before it crosses the event horizon. In addition to stellar black holes that can form after a star burns out its nuclear fuel, supermassive black holes exist at the centers of most galaxies, including the Milky Way.”

He adds, “Theorists like me, however, focus on what black holes can tell us about fundamental questions in physics. The centers of black holes, together with the very early universe, are extreme environments where our current understanding of gravity, based on Einstein’s theory of general relativity, appears to break down. Although we cannot access such regions directly, we test alternative theories, such as string theory, by seeing what they say about questions that general relativity leaves unanswered.” 

Another area of interest is black hole thermodynamics, a field opened up by Stephen Hawking and collaborators in the 1970’s that still poses key open questions, says Kastor. “Isolated black holes are actually very simple, described entirely by their mass, spin and charge. When matter falls in, the evolution of a black hole is governed by laws resembling those of thermodynamics. If one meshes general relativity together with quantum mechanics, it even turns out that black holes radiate energy as if they had a temperature, much like any other hot object. A much-debated question is whether the information contained in the matter that originally formed a black hole is ultimately returned in this Hawking radiation, or whether it is fundamentally lost.”

“My work has addressed many different issues in these contexts over the years, often in collaboration with my UMass colleague and spouse Jennie Traschen. For example, we have explored new types of black hole solutions, called black branes, which play important roles in string theory. Many years ago now Jennie and I found a surprising solution in general relativity that gives an exact description of black holes merging in what is called a deSitter or inflationary background. These became known as Kastor-Traschen spacetimes.”

Kastor and Traschen have explored how the extra dimensions posited by string theory modify the laws of black hole thermodynamics, the role played by the cosmological constant, which may provide the ‘dark energy’ required to account for cosmological observations, in black hole thermodynamics, Lovelock gravity, he says. The latter is “another intriguing way to modify general relativity in the regime of strong spacetime curvature” that is much simpler than string theory and often used as a testbed for exploring how physical properties are modified by changes to general relativity. “Most recently, Jennie and I have been looking at exact solutions for how magnetic fields behave in an expanding universe.”