3 research outputs found
On the number of young stellar discs in the Galactic Centre
Observations of the Galactic Centre show evidence of disc-like structures of
very young stars orbiting the central super-massive black hole within a
distance of a few 0.1 pc. While it is widely accepted that about half of the
stars form a relatively flat disc rotating clockwise on the sky, there is a
substantial ongoing debate on whether there is a second, counter-clockwise disc
of stars.
By means of N-body simulations using our bhint code, we show that two highly
inclined stellar discs with the observed properties cannot be recognised as two
flat circular discs after 5 Myr of mutual interaction. Instead, our
calculations predict a significant warping of the two discs, which we show to
be apparent among the structures observed in the Galactic Centre. While the
high eccentricities of the observed counter-clockwise orbits suggest an
eccentric origin of this system, we show the eccentricity distribution in the
inner part of the more massive clockwise disc to be perfectly consistent with
an initially circular disc in which stellar eccentricities increase due to both
non-resonant and resonant relaxation.
We conclude that the relevant question to ask is therefore not whether there
are two discs of young stars, but whether there were two such discs to begin
with.Comment: 6 pages, 7 figures, accepted for publication in MNRAS Letter
Origin of the S Stars in the Galactic Center
Over the last 15 years, around a hundred very young stars have been observed
in the central parsec of our Galaxy. While the presence of young stars forming
one or two stellar disks at approx. 0.1 pc from the supermassive black hole
(SMBH) can be understood through star formation in accretion disks, the origin
of the S stars observed a factor of 10 closer to the SMBH has remained a major
puzzle. Here we show the S stars to be a natural consequence of dynamical
interaction of two stellar disks at larger radii. Due to precession and Kozai
interaction, individual stars achieve extremely high eccentricities at random
orientation. Stellar binaries on such eccentric orbits are disrupted due to
close passages near the SMBH, leaving behind a single S star on a much tighter
orbit. The remaining star may be ejected from the vicinity of the SMBH, thus
simultaneously providing an explanation for the observed hypervelocity stars in
the Milky Way halo.Comment: 4 pages, 4 figures, accepted for publication in ApJ Letters; final
version, minor changes onl