The effect of impact parameter on tidal disruption events

ABSTRACT Stars that pass too close to a supermassive black hole are disrupted by the black hole’s tidal gravity. Some debris is ejected while the remainder accretes into the black hole. To better study the physics of these debris, we use the moving mesh code manga to follow the evolution of the star from its initial encounter to its complete destruction. By varying the impact parameter (β) of the star, we study the energy distribution of the remaining material and the fallback rate of the material into the black hole as a function of time. We show that the spread of energy in the debris and peak luminosity time (tpeak) are both directly related to the impact parameter. In particular, we find a β1/2 scaling for the energy spread for β = 2 − 10 that levels off at β ≳ 10. We discuss implication of this scaling for the rise time of the light curve and broadness of the luminosity peak for these lower β’s. These relationships provide a possible means of inferring the impact parameters for observed tidal disruption events.

Gravity surveys using a mobile atom interferometer

Mobile gravimetry is important in metrology, navigation, geodesy, and geophysics. Atomic gravimeters could be among the most accurate mobile gravimeters but are currently constrained by being complex and fragile. Here, we demonstrate a mobile atomic gravimeter, measuring tidal gravity variations in the laboratory and surveying gravity in the field. The tidal gravity measurements achieve a sensitivity of 37 μGal/Hz (1 μGal = 10 nm/s2) and a long-term stability of better than 2 μGal, revealing ocean tidal loading effects and recording several distant earthquakes. We survey gravity in the Berkeley Hills with an uncertainty of around 0.04 mGal and determine the density of the subsurface rocks from the vertical gravity gradient. With simplicity and sensitivity, our instrument paves the way for bringing atomic gravimeters to field applications.