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!