33 research outputs found
Hyper Velocity Stars and the Restricted Parabolic 3-body Problem
Motivated by detections of hypervelocity stars that may originate from the
Galactic Center, we revist the problem of a binary disruption by a passage near
a much more massive point mass. The six order of magnitude mass ratio between
the Galactic Center black hole and the binary stars allows us to formulate the
problem in the restricted parabolic three-body approximation. In this
framework, results can be simply rescaled in terms of binary masses, its
initial separation and binary-to-black hole mass ratio. Consequently, an
advantage over the full three-body calculation is that a much smaller set of
simulations is needed to explore the relevant parameter space. Contrary to
previous claims, we show that, upon binary disruption, the lighter star does
not remain preferentially bound to the black hole. In fact, it is ejected
exactly in 50% of the cases. Nonetheless, lighter objects have higher ejection
velocities, since the energy distribution is independent of mass. Focusing on
the planar case, we provide the probability distributions for disruption of
circular binaries and for the ejection energy. We show that even binaries that
penetrate deeply into the tidal sphere of the black hole are not doomed to
disruption, but survive in 20% of the cases. Nor do these deep encounters
produce the highest ejection energies, which are instead obtained for binaries
arriving to 0.1-0.5 of the tidal radius in a prograde orbit. Interestingly,
such deep-reaching binaries separate widely after penetrating the tidal radius,
but always approach each other again on their way out from the black
hole.[shortened]Comment: 10 pages, 10 Figures, Apj submitte
Tidal disruption of inclined or eccentric binaries by massive black holes
Binary stars that are on close orbits around massive black holes (MBHs) such as Sgr A∗ in the centre of the Milky Way are liable to undergo tidal disruption and eject a hypervelocity star. We study the interaction between such an MBH and circular binaries for general binary orientations and penetration depths (i.e. binaries penetrate into the tidal radius around the BH). We show that for very deep penetrators, almost all binaries are disrupted when the binary rotation axis is roughly oriented towards the BH or it is in the opposite direction. The surviving chance becomes significant when the angle between the binary rotation axis and the BH direction is between 0.15π and 0.85π. The surviving chance is as high as ∼20 per cent when the binary rotation axis is perpendicular to the BH direction. However, for shallow penetrators, the highest disruption chance is found in such a perpendicular case, especially in the prograde case. This is because the dynamics of shallow penetrators is more sensitive to the relative orientation of the binary and orbital angular momenta. We provide numerical fits to the disruption probability and energy gain at the BH encounter as a function of the penetration depth. The latter can be simply rescaled in terms of binary masses, their initial separation, and the binary-to-BH mass ratio to evaluate the ejection velocity of a binary members in various systems. We also investigate the disruption of coplanar, eccentric binaries by an MBH. It is shown that for highly eccentric binaries retrograde orbits have a significantly increased disruption probability and ejection velocities compared to the circular binaries
Electromagnetic Window into the Dawn of Black Holes
The origin of massive black holes in the early universe is one of the major puzzles in astrophysics. Future X-ray surveys can detect BHs with mass M < 105 M☉ at z > 10, and OIR observations can characterize their immediate environment. These observations will open a window into the "Dawn of Black Holes" and distinguish models of their origin. <p/
Multimessenger Science Opportunities with mHz Gravitational Waves
LISA will open the mHz band of gravitational waves (GWs) to the astronomy community. Thestrong gravity which powers the variety of GW sources in this band is also crucial in a numberof important astrophysical processes at the current frontiers of astronomy. These range fromthe beginning of structure formation in the early universe, through the origin and cosmic evolutionof massive black holes in concert with their galactic environments, to the evolution ofstellar remnant binaries in the Milky Way and in nearby galaxies. These processes and theirassociated populations also drive current and future observations across the electromagnetic(EM) spectrum. We review opportunities for science breakthroughs, involving either direct coincidentEM+GW observations, or indirect multimessenger studies. We argue that for the UScommunity to fully capitalize on the opportunities from the LISA mission, the US efforts shouldbe accompanied by a coordinated and sustained program of multi-disciplinary science investment,following the GW data through to its impact on broad areas of astrophysics. Supportfor LISA-related multimessenger observers and theorists should be sized appropriately for aflagship observatory and may be coordinated through a dedicated mHz GW research center
Laser Interferometer Space Antenna
Following the selection of The Gravitational Universe by ESA, and the
successful flight of LISA Pathfinder, the LISA Consortium now proposes a 4 year
mission in response to ESA's call for missions for L3. The observatory will be
based on three arms with six active laser links, between three identical
spacecraft in a triangular formation separated by 2.5 million km.
LISA is an all-sky monitor and will offer a wide view of a dynamic cosmos
using Gravitational Waves as new and unique messengers to unveil The
Gravitational Universe. It provides the closest ever view of the infant
Universe at TeV energy scales, has known sources in the form of verification
binaries in the Milky Way, and can probe the entire Universe, from its smallest
scales near the horizons of black holes, all the way to cosmological scales.
The LISA mission will scan the entire sky as it follows behind the Earth in its
orbit, obtaining both polarisations of the Gravitational Waves simultaneously,
and will measure source parameters with astrophysically relevant sensitivity in
a band from below Hz to above Hz.Comment: Submitted to ESA on January 13th in response to the call for missions
for the L3 slot in the Cosmic Vision Programm