the dark side of the universe lecture 26. homework r ead ch. 24: life in the universe h w:...

The Dark Side of

the Universe

Lecture 26

Homework

• Read Ch. 24: Life in the Universe• HW: MasteringAstronomy Chapter 24

Final Exam

• Time: Thursday, Dec 13 at 11:30am in VLSB2050.

Topics: - 25% material covered before midterm 1. - 25% material covered between midterms 1 and 2. - 50% material covered after midterm 2.

Review Session:  Tuesday, Dec 4 at 5pm in VLSB2050 (same room)

Discussion Sectionsand Office Hours

4

Student Evaluations

• Thank you for evaluating the course

and me (Prof. Geoff Marcy)!

Instructor: Geoff Marcy

Course: C12

Semester: Fall 2012

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The Dark Side of

the Universe

Lecture 26

Most of the Universe is Dark

You, me, stars, grey matter,white matter,antimatter…

Example 1: Stars would be moving too fast

if there were only luminous matter

How do we know the Universe is Dark?

Solar System:

“Keplerian orbits”

Earth

Jupiter

Mercury

How do we know the Universe is Dark?

Galaxies:

“Flat rotation curve”

Example 1: Stars would be moving too fast

if there were only luminous matter

Example 2: Bending of light - gravitational lensing

How do we know the Universe is Dark?

How do we know the Universe is Dark?

Four images of the same galaxy

How do we know the Universe is Dark?

How do we know the Universe is Dark?

How do we know the Universe is Dark?

CMB: very cold (-270.275 C, -454.495 F) and nearly uniform relic radiation left over from the hot big bang

Example 3: Cosmic Microwave Background

How do we know the Universe is Dark?

(1965)

If you had microwave eyes:

Example 3: Cosmic Microwave Background

How do we know the Universe is Dark?

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(1992)

(2010)

White points:

WMAP (2010)

7-year data

Red curve: Theoretical prediction for a universe made of73% dark energy, 23% dark matter, 4% atoms

How do we know the Universe is Dark?

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Example 4: Distant supernovae

After

Before

How do we know the Universe is Dark?

Example 4: Distant supernovae are standard candles

How do we know the Universe is Dark?

Example 4: Distant supernovae are standard candles

How do we know the Universe is Dark?

Concordance region:

73% dark energy23% dark matter

4% atoms

How do we know

the Universe is Dark?

Kowalski et al (2008)

Dark Energy

Dark Matter

Supernovae probe

CMB probes

What can dark matter be?

Not enough mass: even Jupiter weighs only

0.1% of the Sun

Rocks, gas, oceans are all made of quarks.

The “normal” stuff cannot be > 4%.

Planets?

What can dark matter be?

Graveyards of massive stars, but massive stars are rare and made of normal atoms.

Once formed, black holes suck in normal matter.

So you can’t hide much dark matter in it.

Black Holes?

What can dark matter be?

Antimatter and matter annihilate each other into flashes of easily detectable gamma rays

Anti-matter?

Hardly “dark” !

Antimatter and matter have identical mass but opposite quantum numbers (electric charge, spin…)

Recall PET = Positron Emission Tomography

What can dark matter be?

Top candidate:

WIMPs

Direct Detection: CDMS-II, Edelweiss etc

Accelerator: Large Hadron Collider

But it takes more than wimps to find WIMPs!

Cryogenic Dark Matter Search

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Supernova Explosionsas

Standard Candles

The distance to the galaxy that contains the supernova: Compare how bright they know the explosion should be with how bright the explosion appears. Using the inverse square law of light, they can compute the distance to the supernova and thus to the supernova's home galaxy.

Type Ia supernovae, which give off a standard amount of light.

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Accelerating Expansion of the Universe:Dark Energy

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LargeHadronCollider

(17 mile tunnel)

Most of the Universe is Dark???

You, me, stars, grey matter,white matter,antimatter…

WIMPS ?