Local Galaxies and Local Galaxies and

Collisions of GalaxiesCollisions of Galaxies

PSC 203PSC 203

OverviewOverview

� In this lecture …In this lecture …� Nearby galaxiesNearby galaxies

� Interactions of galaxiesInteractions of galaxies

ReviewReview

� What galaxy do we live in?What galaxy do we live in?

� What type of galaxy is ours?What type of galaxy is ours?

� What are the other types of galaxies?What are the other types of galaxies?

Milky Way GalaxyMilky Way Galaxy Local Sub-GroupLocal Sub-Group

Nearby GalaxiesNearby Galaxies

� Closest galaxyClosest galaxy� Sagittarius dwarfSagittarius dwarf

� Dwarf ellipticalDwarf elliptical

� Other very close galaxiesOther very close galaxies� Large and Small Large and Small Magellanic cloudsMagellanic clouds

� Irregular galaxiesIrregular galaxies

Sagittarius Dwarf GalaxySagittarius Dwarf Galaxy

� Hard to seeHard to see

� Fairly faintFairly faint

� Spread out on skySpread out on sky

� Other stars in frontOther stars in front

Large Magellanic cloud Small Magellanic cloud

Local Sub-GroupLocal Sub-Grouplocal sub-grouplocal sub-group

� What types of galaxies are in local sub-What types of galaxies are in local sub-

group?group?

� Us, a spiralUs, a spiral

� Mostly dwarf ellipticalsMostly dwarf ellipticals

� Some irregularsSome irregulars

Local GroupLocal Group� The full local group is larger stillThe full local group is larger still

� about 30-40 galaxies about 30-40 galaxies

� about 1 Mpc acrossabout 1 Mpc across

� biggest:biggest:� Andromeda galaxyAndromeda galaxy

� Video,galaxies of the local groupVideo,galaxies of the local group

Andromeda

Interacting GalaxiesInteracting Galaxies

� Definition ...Definition ...

� Galaxies which are close enough for their Galaxies which are close enough for their

mutual gravity to affect each othermutual gravity to affect each other

Interacting GalaxiesInteracting Galaxies� some irregulars form when galaxies some irregulars form when galaxies

interactinteract

� gravity of one pulls on the othergravity of one pulls on the other

� may even collidemay even collide

� video, what happens when galaxies ...video, what happens when galaxies ...

� end result is galaxy or galaxies with end result is galaxy or galaxies with

distortionsdistortions

Collision OverviewCollision Overview

� Gas and dust affected mostGas and dust affected most� Pulled away into strange shapesPulled away into strange shapes

� New star formation triggeredNew star formation triggered

� Stars may be deflectedStars may be deflected� Move to different location in galaxyMove to different location in galaxy

� May be flung out and separate from galaxyMay be flung out and separate from galaxy

� Stars themselves don't collideStars themselves don't collide

SimulationsSimulations

� Simulations often used to predict Simulations often used to predict

interactions...interactions...

� Video, physics simulationVideo, physics simulation

� Video, multiple galaxy collisionVideo, multiple galaxy collision

� Simulations match well to observationsSimulations match well to observations

� video, simulation vs observationvideo, simulation vs observation

Example ImagesExample Images

Example ImagesExample Images Galaxy mergersGalaxy mergers

� Very large galaxies may be due to mergers Very large galaxies may be due to mergers

of many smaller galaxiesof many smaller galaxies

� Video, Hubblecast 16Video, Hubblecast 16

� Slow and gradual processSlow and gradual process

Interactions in the Local GroupInteractions in the Local Group

� Sagittarius dwarf galaxySagittarius dwarf galaxy� Already collided with Milky way and emerged Already collided with Milky way and emerged

from the other side at least once, probably from the other side at least once, probably

more timesmore times

� Video, Sagittarius galaxy fly aroundVideo, Sagittarius galaxy fly around

� Other dwarf galaxiesOther dwarf galaxies� Evidence of other dwarf galaxies already Evidence of other dwarf galaxies already

merged with Milky Waymerged with Milky Way

Milky Way and AndromedaMilky Way and Andromeda

� Andromeda has interacted with its Andromeda has interacted with its

neighborsneighbors

� Milky Way and Andromeda will eventually Milky Way and Andromeda will eventually

interactinteract

� Video, Andromeda, Beauty and the BeastVideo, Andromeda, Beauty and the Beast

Recent evidenceRecent evidence

� Used to think that Andromeda is much Used to think that Andromeda is much

larger than uslarger than us� Andromeda and Milky Way close to same sizeAndromeda and Milky Way close to same size

� Will collide a bit earlierWill collide a bit earlier� Maybe 3 billion years from nowMaybe 3 billion years from now