A cosmic sling-shot mechanism
Johan Samsing
DARK, Niels Bohr Institute, University of
Copenhagen
Outline
• 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!
Before:
After:
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.
Merger:
Ejection:
Reduced a highly nonlinear problem down to
a simple physical
mechanism!
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?
(pos,vel)
Time ->
z=0
Particles in an Expanding Universe
Total acceleration:
BG: attracting
BG: repelling
Halo mass:
Expansion
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
distributions
Such as: infall, virialized
matter, caustics etc.
Conclusions
• 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!