138 research outputs found
Globular Clusters and Dark Satellite Galaxies through the Stream Velocity
The formation of purely baryonic globular clusters with no gravitationally
bound dark matter is still a theoretical challenge. We show that these objects
might form naturally whenever there is a relative stream velocity between
baryons and dark matter. The stream velocity causes a phase shift between
linear modes of baryonic and dark matter perturbations, which translates to a
spatial offset between the two components when they collapse. For a 2sigma
(3sigma) density fluctuation, baryonic clumps with masses in the range 1e5 -
2.5e6 Msun (1e5 - 4e6 Msun) collapse outside the virial radii of their
counterpart dark matter halos. These objects could survive as long-lived dark
matter-free objects and might conceivably become globular clusters. In
addition, their dark matter counterparts, which were deprived of gas, might
become dark satellite galaxies.Comment: 3 Figures, accepted for publication in ApJ Letter
Formation of Dark Matter Torii Around Supermassive Black Holes Via The Eccentric Kozai-Lidov Mechanism
We explore the effects of long term secular perturbations on the distribution
of dark matter particles around Supermassive Black Hole (BH) binaries. We show
that in the hierarchical (in separation) three-body problem, one of the BHs and
a dark matter particle form an inner binary. Gravitational perturbations from
the BH companion, on a much wider orbit, can cause the dark matter particle to
reach extremely high eccentricities and even get accreted onto the BH, by what
is known as the Eccentric Kozai-Lidov (EKL) mechanism. We show that this may
produce a torus-like configuration for the dark matter distribution around the
less massive member of the BH binary. We first consider an Intermediate BH
(IMBH) in the vicinity of our Galactic Center, which may be a relic of a past
minor merger. We show that if the IMBH is close enough (i.e., near the stellar
disk) the EKL mechanism is very efficient in exciting the eccentricity of dark
matter particles in near-polar configurations to extremely high values where
they are accreted by the IMBH. We show that this mechanism is even more
effective if the central BH grows in mass, where we have assumed adiabatic
growth. Since near-polar configurations are disrupted, a torus-like shape is
formed. We also show that this behavior is also likely to be relevant for
Supermassive BH binaries. We suggest that if the BHs are spinning, the accreted
dark matter particles may linger in the ergosphere and thereby may generate
self-annihilations and produce an indirect signature of potential interest.Comment: Accepted to ApJ, 11 pages, 9 figure
Mergers and Obliquities in Stellar Triples
Many close stellar binaries are accompanied by a far-away star. The
"eccentric Kozai-Lidov" (EKL) mechanism can cause dramatic inclination and
eccentricity fluctuations, resulting in tidal tightening of inner binaries of
triple stars. We run a large set of Monte-Carlo simulations including the
secular evolution of the orbits, general relativistic precession and tides, and
we determine the semimajor axis, eccentricity, inclination and spin-orbit angle
distributions of the final configurations. We find that the efficiency of
forming tight binaries (<~16 d) when taking the EKL mechanism into account is ~
21%, and about 4% of all simulated systems ended up in a merger event. These
merger events can lead to the formation of blue-stragglers. Furthermore, we
find that the spin-orbit angle distribution of the inner binaries carries a
signature of the initial setup of the system, thus observations can be used to
disentangle close binaries' birth configuration. The resulting inner and outer
final orbits' period distributions, and their estimated fraction, suggests
secular dynamics may be a significant channel for the formation of close
binaries in triples and even blue stragglers.Comment: Accepted to ApJ, 10 figure
Ultra wide black-hole - neutron star binaries as a possible source for gravitational waves and short gamma ray bursts
The third observing run of the LIGO/Virgo/KARGA collaboration reported a few
neutron star - black hole (NSBH) merger events. While NSBH mergers have yet to
receive extensive theoretical attention, they may have a promising
electromagnetic signature in the form of short gamma - ray bursts. Here we show
that NSBH dynamical mergers can naturally form from ultra - wide binaries in
the field. Flyby gravitational interactions with other neighbors in the galaxy
in these ultra - wide systems may result in high eccentricity that drives the
binary into a merger. We show that this process can result in a merger rate at
the order of ~Gpc~yr (~Gpc~yr) for
elliptical (spiral) galaxies. This channel predicts higher merger rate with
higher velocity dispersion of the host - galaxy, delay time distribution which
shallower than uniform but steeper that , higher merger rate for lower BH
to NS mass ratio
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