Effects of a Black Hole

Motivation for our work comes from the presence of massive

black holes in galactic nuclei and from the possibility that such

black holes accrete material from their surroundings. It was

estimated (Gurzadyan & Ozernoy 1981; Rees 1990; Magorrian

& Tremaine 1999; Syer & Ulmer 1999) that central black holes

may capture stars from inner ga

lactic regions at the rate from

10



3

to 10



7

stars per galaxy per year. Such events would be

particularly interesting in the Galactic center, where the ob-

served X-ray flare (Baganoff et al. 2001) and measured motion

of stars, down to only 17 lt-hr from the center (Scho

̈del et al.

2002), provide strong evidence that the central concentration of

about 3

;

10

6

M

is indeed a black hole. In recent years UVand

X-ray flares have been observed in the nuclei of NGC 4552,

NGC 5905, RX J1242.6



1119, RX J1624.9+7554, and others,

for which it was concluded that tidal disruption of a star by a

massive black hole provides the best explanation (Renzini et al.

1995; Komossa & Bade 1999; Grupe et al. 1999; Gezari et al.

2003).

The interaction of a star with a black hole has been studied

previously by other authors (Rees 1988; Carter & Luminet

1985; Luminet & Marck 1985) with a number of detailed hy-

drodynamic simulations (Laguna et al. 1993; Khokhlov et al.

1993a, 1993b; Kochanek 1994; Fulbright et al. 1995; Marck

et al. 1996; Diener et al. 1997; Loeb & Ulmer 1997; Ayal et al.

2000; Ivanov & Novikov 2001; Ivanov et al. 2003) with em-

phasis on stellar structure during the encounter with the black

hole and long-term evolution of stellar debris. Nevertheless, none

of these studied the luminosity variations occurring to the star in

the vicinity of the black hole. In order to be complete, such a study

should include stellar hydrodynamics in full general relativity,

modeling of radiation processes in the disrupted star, and rela-

tivistic effects on the emitted light. Because of the complexity of...