A cosmic sling-shot mechanism

A cosmic sling-shot mechanism
Johan Samsing
DARK, Niels Bohr Institute, University of
• The Dynamical Sling-Shot Mechanism.
• Previous work and motivations.
• Movie of a DM halo merger!
• An ejected particle in an expanding universe.
• Modeling of the mass ejection history.
• The field outside the virial radius.
• Phase-space distribution of ejected particles.
Gravitational Sling-Shot Mechanism
•Basic Idea:
- In few body system you can exchange energy between particles.
Gravitational Sling-Shot Mechanism
• You can speed particles up to high energies.
• Positive energy comes from increasing binding energy.
Gravitational Sling-Shot Mechanism
• Speeding up probes in the solar system.
• Gains of order 10 km/sec per passage
Exchange energy with planets
Example: Cassini’s trip to Saturn
Gravitational Sling-Shot Mechanism
• Gravitational wave sources are build this way!
• GRBs are very likely collisions between NSs.
• Few-body interactions could (is) be future to probe fundamental physics!
Dynamical Mechanism:
• SN/stars with no host and hypervelocity stars.
• http://arxiv.org/abs/1102.0007 ‘Cosmology with Hypervelocity Stars’- Avi Loeb.
Galaxy dominate
Cosmology dominates
• Can we do something similar but with the current observed field?
• How is the tracers created?
This work: Galaxy Mergers
• We consider dark matter mergers - a highly non-linear feature.
• Particles are kicked out by an effect similar to the 3-body sling-shot.
Reduced a highly nonlinear problem down to
a simple physical
A Few Motivations
Whole community (try to) calculate DM steady state: here we show part of the
particles are distributed according to simple sling-shot effect. It’s a great and
funny mechanical problem!
Recent work by e.g. Beehzori, Wechsler, Loeb describe fraction of unbound
particles in halos. They don’t include any dynamical arguments or history of
the ejected particles.
Direct DM experiments can be very sensitive to the high energy part of the
DM distribution.
Observations of hyper velocity stars/gas/galaxies.
Observations: - Mapping the halo by stacking – use BG sources e.g. QSO and
absorption lines – Stellar evolution and ejection age etc. – Outskirts of clusters
can hold enormous information! Don’t restrict yourself to the virial sphere!
Movie: MOVIE!
DM halo merger
Ejected or Trapped?
Ejected particles:
Passes the center when the
potential is declining.
Orbits are analytically known for some profiles.
Trapped particles:
Cant escape!
A Few Fundamental Questions:
How far do they travel?
What is their distribution today?
What is the ‘halo-horizon’?
What are the dynamical signatures in phase-space?
Time ->
Particles in an Expanding Universe
Total acceleration:
BG: attracting
BG: repelling
Halo mass:
Position and velocity at z=0
What is the most likely regime?
Depends on cosmology!!
Ejection Velocity and Mass Rate
Mass ejection rate:
Merger rate (Fakhouri et al. 2010):
Ejection velocity:
Mass, Ejection Age and Distance
• Inverse age-distance
relation compared to
virialized part of the halo.
• Looking into the outer
parts is looking back in time
– ‘cosmic fossils’.
• Can be mapped out using
background sources, e.g.,
QSOs (working on that).
• Slingshot mechanism only
way to reach such distances!
Phase Space Distribution
• Depends on:
- Cosmology.
- accretion history.
• Distribution:
- Is distributed in another
part of phase space
compared to usual
Such as: infall, virialized
matter, caustics etc.
• Classical slingshot mechanism ejects particles into large orbits where
cosmology takes over.
• Funny mechanics problem that can explain the distribution of high energy
particles - no need for any fancy statistical mechanics. Large part of the
particles distribute according to this mechanism!
• New dynamical component and tracer of the field that can be studied
around galaxy clusters.
• Could motivate observers to look for ‘host-less’ galaxies, gas etc.
• If map out in detail – reveals formation history and the interplay between BG
and host halo gravitational field.
•Most of all: a highly complex system can be reduced to a simple physical
mechanism that plays a role on all scales in our universe! A fun problem!

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