GALAXIES:! Island !

"Universes"!

Stephen Perrenod, Ph.D.

What is a Galaxy?

Gravitationally bound !system of:!

!Stars!

Planets!Gas!Dust!

!"Dark Matter" (mostly!)

3 Major Types of Galaxies

Elliptical - M87!!

Spiral - M101!!

Irregular - NGC1427A

Image credit: X-ray: NASA/CXC/SAO; Optical: Detlef Hartmann; Infrared: NASA/

JPL-Caltech

Our Galaxy: The Milky Way200 to 400 Billion Stars!

!A Spiral Shape!

!Size 100,000+ light-year

Diameter !(Only 1000 thickness)!

!Sun distance to center, 27,000

light-years!!

Rotates once per 240 million years

Portion of #Milky Way

NGC 6744

Milky Way!SchematicBar, Spiral Arms &!

You are Here!

Our Neighbor: Andromeda Galaxy

Distance - 2.5 Million light-years!

!Size - 220,000 light-years!

!Will collide with us in ~4

Billion years!

M31

Andromeda Attacks!

Lots of time to prepare..

The Magellanic Clouds

Southern Hemisphere objects, visible to the naked eye!

!About 200,000 light-years away!

!Large Magellanic Cloud is 14,000 light-years in size!

!Small Magellanic Cloud size is

7,000 light-years

The Local Group

Our neighborhood!!!

10 million light-years across!

!Will coalesce eventually

into one Supergalaxy!!

Rich Cluster of Galaxies~ 1000 galaxies bound together!

!Along with dark matter and gas!

!High gravitational potential heats gas to 100

million degrees!!

X-ray emission

Abell 2218

Stellar Factories

Galaxies are Huge!!

They are old ~ 13 billion years!!

They are factories for star formation and planet

formationOrion #

Nebula

Why Galaxies?

Galaxies exist so that multiple generations of stars

can be created!!

Stars exist to create elements for, and provide heat and

light to, planets!!

Planets exist as friendly abodes for life:!Including You!

Dark Matter

Our galaxy is mostly made of mysterious "Dark Matter"!

!Not stars or light-emitting

gas, but gravitational effects seen!!

All galaxies and clusters of galaxies are like this!

!Harvard computer simulation

What does "Dark Matter" mean?

Simply, matter that is hard to detect because

it doesn't emit light!!

But it has mass, so has gravitational effects!

!Thought to be some

kind of new, unknown matter

Abell 1689

Ways to Detect Dark Matter's Gravitational Effects

Galaxy rotation curves!!

Clusters of galaxies, X-ray emission!

!Gravitational lensing

How Much DM is there?

5 times as much as all ordinary matter!

What is it composed of?

We don't know!!!

NOT candidates: faint stars, black holes, dust, planets, lumps of coal!

!Candidates are all hypothetical new particles!!

!WIMPs (LSP - neutralinos)!

Axions!Sterile neutrinos

Thank you!

Cosmology blog:#darkmatterdarkenergy.com