Download - A cosmic sling-shot mechanism Johan Samsing DARK, Niels Bohr Institute, University of Copenhagen
• 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.
Outline
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.
• Can we do something similar but with the current observed field?• How is the tracers created?
Galaxy dominate Cosmology dominates
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 non-linear 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!
Ejected or Trapped?Ejected particles: Passes the center when the potential is declining.
Trapped particles:Cant escape!
Orbits are analytically known for some profiles.
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 -> z=0
(pos,vel)
Particles in an Expanding Universe
Total acceleration:
Halo mass:
Expansion
BG: attracting BG: repelling
Ejection Velocity and Mass Rate
Mass ejection rate: Ejection velocity:
Merger rate (Fakhouri et al. 2010):
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 anotherpart of phase spacecompared to usual distributionsSuch 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!