Phoenix Lander lands at the pole on Sunday !!

Admin Review lecture today (and posted on the web) Final Exam:

10:30am May 28th (Wednesday), SHL 131 Will cover:

1, 2, 3, 4, 5, 10, 11, 12, 15.1, 15.2, 15.3, 16.1, 16.2 Extra Office Hours

2:00pm – 4:00pm May 27th (Tuesday), SHL 222 Or email/ come and find me.

• An answer with no units is meaningless

• Getting the units/order of magnitude wrong is not a minor mistake.

Units are important!!!

What is the energy, in Joules, of an ultra-violet photon with a wavelength of 120nm? What is its frequency?

f= c/ = 3 108 / 12010-9 = 2.5 1015 Hz E=hf = 6.626 10−34 2.5 1015 =1.66 10-18 J

Kilo=103 milli=10-3

Mega=106 micro=10-6

Giga=109 nano=10-9

See appendix C3 and appendix C4 in the book

Summary of Star Birth

1. Gravity causes cold, dense, molecular gas cloud to shrink and fragment

2. Dust relieves thermal pressure by radiating infra-red

3. Collapses into a rotating disk (conservation of angular momentum)

4. Core of shrinking cloud heats up

5. When core gets hot enough, fusion begins and stops the shrinking

6. New star achieves long-lasting state of balance

What is the energy source that heats a contracting protostar?

1. Friction

2. Pressure, as the gas and dust are compressed

3. Gravitational potential energy released as the material is pulled inward

4. Fusion

5. Kinetic energy

What is the energy source that heats a contracting protostar?

1. Friction

2. Pressure, as the gas and dust are compressed

3. Gravitational potential energy released as the material is pulled inward

4. Fusion

5. Kinetic energy

If a protostar doesn’t have enough mass to become a star, it becomes a

1. Failed star

2. Dark star

3. Brown dwarf

4. White dwarf

5. Planetesimal

If a protostar doesn’t have enough mass to become a star, it becomes a

1. Failed star

2. Dark star

3. Brown dwarf

4. White dwarf

5. Planetesimal

Low-Mass Star Summary

1. Main Sequence: H fuses to He in core. (solar thermostat)

2. Red Giant: H fuses to He in shell around He core (thermostat broken!!)

3. Helium Core Burning: He fuses to C in core while H fuses to He in shell

• Double-Shell Burning: H and He both fuse in shells

5. Planetary Nebula: leaves white dwarf behind

Not to scale!

Life stages of a low-mass star like the Sun

The Death Sequence of the Sun

Life Track of a Sun-Like Star

After the Sun becomes a red giant star and makes carbon in its core, why will it not make heavier

elements?1. It will have run out of fuel

2. It will be near the end of its life and doesn’t have time

3. It will not be massive enough to make it hot enough for further reactions

4. The heavier elements will all go into a planetary nebula

5. 1 and 2

After the Sun becomes a red giant star and makes carbon in its core, why will it not make heavier

elements?

1. It will have run out of fuel

2. It will be near the end of its life and doesn’t have time

3. It will not be massive enough to make it hot enough for further reactions

4. The heavier elements will all go into a planetary nebula

5. 1 and 2

Life Stages of High-Mass Star

1. Main Sequence: H fuses to He in core

2. Red Supergiant: H fuses to He in shell around He core

3. Helium Core Burning: He fuses to C in core while H fuses to He in shell

4. Multiple-Shell Burning: many elements fuse in shells

5. Supernova leaves neutron star or black hole behindNot to scale!

Multiple-Shell Burning• Advanced nuclear

burning proceeds in a series of nested shells.

• As each core fusion stops, the star expands

• The star is now a multiple shell-burning supergiant

• Works as far as iron

What is different about nuclear reactions of elements lighter than iron or heavier than iron?

1. Lighter elements give off energy when they fuse, heating the stars core and keeping gravity from crushing it

2. Heavier elements take in energy if they fuse, taking away heat from the core, leading to collapse

3. 1 and 2

What is different about nuclear reactions of elements lighter than iron or heavier than iron?

1. Lighter elements give off energy when they fuse, heating the stars core and keeping gravity from crushing it

2. Heavier elements take in energy if they fuse, taking away heat from the core, leading to collapse

3. 1 and 2

Supernova Remnant

• Energy released by the collapse of the core drives outer layers into space, forming a supernova remnant.

• The core becomes a neutron star or a black hole

The distance of the red supergiant Betelgeuse is approximately 427 light-years. If it were to explode as a supernova, it would be one of the brightest stars in the sky. Right now, the brightest star other than the Sun is Sirius, with a luminosity of 26 LSun and a distance of 8.6 light-years. How much brighter than Sirius would the Betelgeuse supernova be in our sky if it reached a maximum luminosity of 8.0×109 LSun ?

52

9

2

2

9

2

102.16.8427

26100.8

6.84

26

4274

100.8

4

sirius

SN

sunsirius

sunSN

b

b

Lb

Lb

d

Lb

Irregular Galaxies

Hubble Ultra Deep Field

Spiral Galaxy

Elliptical GalaxyElliptical Galaxy

Blue-white color indicates ongoing star formation

Red-yellow color indicates older star population

Disk Component:stars of all ages,many gas clouds

Spheroidal Component:bulge and halo, old stars,few gas clouds

Elliptical Galaxy: All spheroidal component, virtually no disk component. Very little dust or cool gas.

Red-yellow color indicates older star population.

Blue-white color indicates ongoing star formation.

Irregular Galaxy: Neither spiral nor elliptical. More common at large distances (in the early Universe)

Hubble’s galaxy classes"Tuning Fork" diagram

SpheroidDominates

Disk Dominates

Which type of galaxies have a disk, bulge, andhalo?

1. Spiral

2. Elliptical

3. Irregular

4. Barred Spiral

5. 1 and 4

Which type of galaxies have a disk, bulge, andhalo?

1. Spiral

2. Elliptical

3. Irregular

4. Barred Spiral

5. 1 and 4

How do we measure the distances to galaxies?

Standard candles:You measure a star's apparent brightness to be 1.010-12 watt/m2.The star has the same spectral type and luminosity as the sun.How far away is it?

LSun=3.81026 Watts

m105.51014

108.3

4

4

1812

26

2

b

Ld

d

Lb

but sun-type stars are not very bright....

Step 3

Apparent brightness of star cluster’s main sequence tells us its distance. (Many stars give a more accurate answer than just one)

Hyades distance known from parallax

Pleiades must besqrt(7.5)=2.75 times further

Hubble’s law: velocity = H0 distanceH0=22 km/s/Mly

Redshift of a galaxy tells us its distance through Hubble’s law:

distance = velocity

H0

Example: the redshift of a galaxy indicates it is moving away at 66,000 km/s. What is its distance?

€

d =v

H0

=66,000 km/s

22 km/s/Mly= 3,000 Mly

Hubble’s constant tells us the age of the universe because it relates velocities and distances of all galaxies.

Age =

~ 1 / H0

Distance

Velocity

Hubble’s law: velocity = H0 distanceH0=22 km/s/Mly

years1036.1km/s 22

years )10(3101

years )10(310

km/s22

ly10

km/s 22

1056

0

5660

HAge

H

Galaxy Evolution

• How do we observe the life histories of galaxies?— Deep observations of the universe are

showing us the history of galaxies because we are seeing galaxies as they were at different ages.

• How did galaxies form?— Our best models for galaxy formation

assume that gravity made galaxies out of regions of the early universe that were slightly denser than their surroundings.

Galaxy Evolution

• Why do galaxies differ?— Some of the differences between galaxies

may arise from the conditions in their protogalactic clouds (spin, density).

— Collisions can play a major role because they can transform two spiral galaxies into an elliptical galaxy.

Chapter 16Dark Matter, Dark Energy, and

the Fate of the Universe

Dark matter: An undetected form of mass that emits little or no light but whose existence we infer from its gravitational influence

Dark energy: An unknown form of energy that seems to be the source of a repulsive force causing the expansion of the universe to accelerate

Unseen Influences

• “Normal” matter: ~ 4.4%— Normal matter inside stars: ~ 0.6%

— Normal matter outside stars: ~ 3.8%

• Dark matter: ~ 22%• Dark energy: ~ 74%

Contents of Universe

Spiral galaxies all tend to have flat rotation curves indicating large amounts of dark matter.

The visible portion of a galaxy lies deep in the heart of a large halo of dark matter.

• Ordinary Dark Matter (MACHOS)— Massive Compact Halo Objects:

dead or failed stars in halos of galaxies

• Extraordinary Dark Matter (WIMPS)— Weakly Interacting Massive Particles:

mysterious neutrino-like particles

Two Basic Options

The Best Bet