Galaxies_BigBang_Dark Matter

Galaxies, The Big Bang

& Dark Matter

Stephen Perrenod, Ph.D.

Interstellar Intergalactic!

What is a Galaxy?

Gravitationally bound system of:

StarsPlanets

GasDust

"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

Sun orbits around center once in 240 million years

Portion of Milky Way

NGC 6744

Milky Way: Latest Star Map

Density map of stars in a portion of the Milky Way disk

New catalog from the Isaac Newton Telescope

219 million stars mapped

10 years of data!

Credit: Hywel Farnhill, University of Hertfordshire

Milky WaySchematic

Top Down View:

Bar, Spiral Arms &You are Here!

Milky WaySchematic

Side View:

Disk, Bulge, Halo &You are Here!

Disk: ~100 billion solar massesBulge: ~10 billion solar massesHalo: ~1 trillion solar masses

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

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!

Stellar Factories

Galaxies are Huge

They are old ~ up to 13 billion years

They are factories for star formation and planet

formation Orion Nebula

Life Cycle of Stars

Main Sequence—-

White DwarfNeutron StarBlack Hole

Ages of Earth, Universe

Age of Earth = 4.6 billion years

Age of Universe = 13.8 billion years

Age of Universe ~ 3 * Age of Earth

Cosmology: Study of Universe as a Whole

Big Bang:

Homogenous, expanding universe

Finite age

Same laws of physics everywhere

Key Dates: Big Bang theory

1912: Galaxy redshifts (V. Slipher)

1915: General Relativity (A. Einstein)

1922: Friedmann equations (A. Friedmann)

1927: Expanding Universe (G. Lemaitre)

1929: Hubble Diagram, Law (E. Hubble)

1964/5: Cosmic Microwave Background Radiation (A. Penzias & R. Wilson)

RedshiftLight is shifted toward the red, if the distant galaxy is moving away

from our galaxy(Almost all are!)

V = c * z (Small z)

c = 300,000 km/s

Distant galaxy

e.g. a few percent of c

Hubble Diagram: 1929

Plot of velocity (recession speed) vs. distance

Hubble's estimate: 500 kilometers/sec/Megaparsec

Megaparsec ~ 3.26 million light-years

Nearest star 4.2 light years

Sun 8 light-minutes

~ Millions of light-years

Hubble's Law

V = H * D

Speed of recession is proportional to distance

H = Hubble's constant

H = 68 km/sec/Mpc (units are inverse time)

Age of Universe

T (now) = 1 / H(now) = 13.8 billion years

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

particle (or more than one)

Abell 1689

Ways to Detect Dark Matter's Gravitational Effects

Galaxy rotation curves

Clusters of galaxies, X-ray emission

Gravitational lensing

How Much Dark Matter is there?

5 times as much as all ordinary matter!

Dark

Ordinary

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!Weakly Interacting Massive Particles:

NeutralinosAxions

Sterile neutrinoss-quark matter

CDMS-IISi wafers

3 particles?

Thank you!

Cosmology blog:darkmatterdarkenergy.com

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