Special CRA Seminar Michael Eracleous – Penn State 11am-12 noon

Title: Gravitational Wave and Electromagnetic Signals Associated With the Tidal Disruption of White Dwarfs

Abstract:

I will discuss the gravitational-wave and electromagnetic signals expected to accompany the tidal disruption of a white dwarf by a massive (i.e., “intermediate mass” black hole). Since white dwarfs are very compact, they can only be disrupted outside of the horizon of a black hole that less massive than about 10⁵ M_⦿ (if it is not spinning; up to 10⁶ M_⦿, if it is maximally spinning). As such, their disruptions can serve as signposts of black holes in this intermediate mass range.  The gravitational wave signal from the disruption of a white dwarf in an unbound orbit is a brief burst while the optical spectroscopic signature of such an event is arguably unique and can be used to identify it. Things get more interesting if the white dwarf is captured in a bound orbit before it is disrupted. Such encounters are likely the most common type of an extreme mass ratio inspiral. In such a scenario, the gravitational wave signal is a “slow chirp” that traces the gradual decay of the orbit, it can last for months to years, and is detectable by LISA. Therefore, observers will have ample advance warning to get ready to catch (quasi-)periodic electromagnetic emission that may precede the disruption and the electromagnetic flare that accompanies and follows the disruption.