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A cosmic sling-shot mechanism

A cosmic sling-shot mechanism. Johan Samsing DARK, Niels Bohr Institute, University of Copenhagen. O utline. The Dynamical Sling-Shot Mechanism. Previous work and motivations. Movie of a DM halo merger! An ejected particle in an expanding universe.

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A cosmic sling-shot mechanism

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  1. A cosmic sling-shot mechanism Johan Samsing DARK, Niels Bohr Institute, University of Copenhagen

  2. 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.

  3. Gravitational Sling-Shot Mechanism • Basic Idea: • - In few body system you can exchange energy between particles.

  4. Gravitational Sling-Shot Mechanism • You can speed particles up to high energies. • Positive energy comes from increasing binding energy.

  5. 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

  6. 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:

  7. 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?

  8. 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: Reduced a highly non-linear problem down to a simple physical mechanism! Ejection:

  9. 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!

  10. MOVIE! Movie: DM halo merger

  11. Ejected or Trapped? Ejected particles: Passes the center when the potential is declining. Orbits are analytically known for some profiles. Trapped particles: Cant escape!

  12. 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) z=0 Time ->

  13. Particles in an Expanding Universe Total acceleration: BG: attracting BG: repelling Halo mass: Expansion

  14. Position and velocity at z=0 What is the most likely regime? Depends on cosmology!!

  15. Ejection Velocity and Mass Rate Mass ejection rate: Ejection velocity: Merger rate (Fakhouri et al. 2010):

  16. 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!

  17. 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.

  18. 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!

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