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 Kostic_etal2.tex A&A, 496, 307-315 (2009)
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\title{Tidal effects on small bodies by massive black holes}
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\author{
Uro\v s Kosti\' c
\inst{1}
\and
Andrej \v Cade\v z
\inst{1}
\and
Massimo Calvani
\inst{2}
\and
Andreja Gomboc
\inst{1}
}
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\offprints{U. Kosti\' c, \email{uros.kostic@fmf.uni-lj.si}}
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\institute{Faculty of Mathematics and Physics, University of Ljubljana,
Jadranska 19, 1000 Ljubljana, Slovenia
\and
INAF - Astronomical Observatory of Padova, Vicolo
Osservatorio 5, 35122 Padova, Italy
}
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\date{Received ?? / Accepted ??}
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\abstract
{The compact radio source Sagittarius $\mathrm{A}^*$
(\mbox{Sgr~$\mathrm{A}^*$}) at the centre of our Galaxy harbours a
supermassive black hole, whose mass ($\approx 3.7 \times 10^6 M_{\sun}$)
has been measured from stellar orbital motions.
\mbox{Sgr~$\mathrm{A}^*$}\ is therefore the nearest laboratory where
super-massive black hole astrophysics can be tested, and the environment
of black holes can be investigated. Since it is not an active galactic
nucleus, it also offers the possibility of observing the capture of
small objects that may orbit the central black hole.}
{We study the effects of the strong gravitational field of the black
hole on small objects, such as a comet or an asteroid. We also explore
the idea that the flares detected in \mbox{Sgr~$\mathrm{A}^*$}\ might be
produced by the final accretion of single, dense objects with mass of
the order of $10^{20}\ \mathrm{g}$, and that their timing is not a
characteristic of the sources, but rather of the space-time of the
central galactic black hole in which they are moving.}
{The problem of tidal disruption of small objects by a black hole is
studied numerically, using ray-tracing techniques, in a Schwarzschild
background.}
{We find that tidal effects are strong enough to melt sufficiently
massive, solid objects, and present calculations of the temporal
evolution of the light curve of infalling objects as a function of
various parameters. Our modelling of tidal disruption suggests that
during tidal squeezing, the conditions for synchrotron radiation can be
met. We show that the light curve of a flare can be deduced from
dynamical properties of geodesic orbits around black holes and that it
depends only weakly on the physical properties of the source.}
{}
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\keywords{Galaxy: nucleus -- Galaxies: active -- Physical data and
processes: black hole physics}
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\titlerunning{Black hole's tidal effects}
\authorrunning{Kosti\' c et al.}
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\maketitle
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\section{Introduction}
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\section{Small bodies at the Galactic center}
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\section{Tidal disruption of a small body and resulting light curves}
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\subsection{Numerical code}
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\subsection{Results}
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\section{Discussion}
\label{sec:discussion}
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\subsection{The effects of magnetic field}
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\subsection{Flares}
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\section{Conclusions}
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\begin{acknowledgements}
U.~K., A.~\v C. and M.~C. acknowledge support from the bilateral
protocol of scientific and technological cooperation between Italy and
Slovenia. U.~K., A.~\v C. and A.~G. acknowledge partial support from the
grant 1554-501 of the Slovenian Research Foundation.
\end{acknowledgements}
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