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Home , Andromeda Galaxy, Antennae Galaxies, HCG 87, Luminous infrared galaxy, NGC 4565

When Collide

Institute for Open House April 29, 2007 The from Mauna Kea

The Milky Way from the Onizuka Center on Mauna Kea, May 2001. Barney Magrath. The Milky Way

All-sky view of the Milky Way. Axel Mellinger. Milky Way in Light

Milky Way in IR. COBE, NASA. The “Needle” Galaxy

Edge-on NGC 4565 in . ARGO Cooperative Observatory. A Spiral Galaxy

Spiral Galaxy NGC 4414 in Canes Venatici. HST, NASA. The “Sombrero” Galaxy

Spiral galaxy NGC 4594 in Virgo. HST, NASA. An

Elliptical galaxy NGC 4486 in Virgo. CFHT. Peculiar Galaxies

An assortment of peculiar galaxies. John Hibbard, NRAO. A Galactic Collision

Colliding galaxies NGC 520. Gemini Observatory, AURA, NSF. The “Tadpole” Galaxy

The “Tadpole” galaxy, UGC 10214. HST, NASA. Tidal Interactions

SPIN

–0.5 0 0.5 1

1.5 2 2.5 3

Simple model of galactic collision. Alar & Juri Toomre (1972). Tidal Simulation Tidal Simulation The “Whirlpool” Galaxy

The “Whirlpool” Galaxy, NGC 5194, and its companion, NGC 5195. HST, NASA. Deep Time

From start to finish, a galaxy collision takes about a billion years.

For comparison:

• Recorded human history spans five thousand years. • Humans evolved half a million years ago. • Dinosaurs became extinct sixty-five million years ago. • Fish began evolving half a billion years ago. • Life first appeared on about four billion years ago. • The is four and a half billion years old. • The is almost fourteen billion years old. The “Antennae” Galaxies

The “Antennae” galaxies, NGC 4038/39. HST, NASA and Francois Schweizer, OCIW. Antennae Simulation The “Mice”

The Mice, NGC 4676. HST, NASA. (inset: John Hibbard, UH 88”) The Mice: Computer Simulation The “Atoms for Peace” Galaxy

The “Atoms for Peace” galaxy, NGC 7252. John Hibbard, NRAO. Merger Simulations

Merger simulations. Barnes (1992). What Happens to and Planets?

NOTHING!

Stars are so far apart that the chances of a collision are practically zero. Planetary collisions are even less likely.

Planetary systems are at slightly greater risk, because a passing can disrupt planetary orbits even without hitting anything. But the chances of this during a galactic collision are no greater than they are at other times. The “Exploding Cigar” Galaxy

NGC 3031 and NGC 3034. Robert Gendler. The “Exploding Cigar” galaxy, NGC 3034. HST, NASA. , a “ Factory”

Arp 299. Aaron Evans, HST, NASA. , an Ultra-

Arp 220 and surroundings. John Hibbard, NRAO. Arp 220 in infrared light. HST, NASA. Merger Simulations With “Gas”

Mergers with gas. Barnes & Hernquist (1996). Merger With Black Holes

Tiziana Di Matteo (MPE/CMU), Volker Springel (MPE) & Lars Hernquist (Harvard) A Compact Group of Galaxies

HCG 87, a compact group of spiral and elliptical galaxies. HST, NASA. Stephan’s Quintet

Stephan’s Quintet, a compact group of galaxies. HST NASA, ESA. Compact Group Simulation

Simulation of a compact group. Barnes (2000). A

A distant cluster of galaxies. VLT, ESO. Mergers Long Ago and Far Away

Mergers in a cluster 8 billion light years away. HST, NASA. Past and Future of the Milky Way

Milky Way Galaxy. 2MASS. The Sagittarius Dwarf: an Ongoing Merger

M54

REU Program/NOAO/AURA/NSF

Milky Way (blue) and debris from Sagittarius Dwarf (red). David Law, University of Virginia. : A Future Merger

The , NGC 224. Robert Gendler. The Fate of the Milky Way

John Dubinski (CITA) & Lars Hernquist (Harvard). Thank You!