astro 113 week3 - Department of Physics and...

Astronomy 113Dr. Joseph E. Pesce, Ph.D.

© Dr. Joseph E. Pesce, Ph.D.

The Sun


10-2

The Sun³ The nearest star - easiest to study - use as a model³ The Atmosphere

1. Photosphere - the visible layer (about 400km thick)q Low density (0.01% of our atmosphere at sea level)q Perfect blackbody at 5800 Kq Can’t see belowq Features:

Granulation Limb Darkening

Proof that Sun is made of gas (not solid)© Dr. Joseph E. Pesce, Ph.D.

10-3

The Sun³ The Atmosphere

2. Chromosphere - layer of less dense gas above the photosphere (about 500km thick)q T ~ 4000 Kq Features:

Spicules - spikes or jets of gas


10-4


3. Corona - upper most layer of atmostphere; extends to millions of km q Very low densityq Can be seen during eclipsesq T ~ 2 x 106 Kq Heated by magnetic fieldsq So hot particles have high velocities and escape as solar wind (p &

e-): 1 million tons per second!!

photosphere

interior

chromosphere

spiculecorona


10-5


² Sunspots - cooler regions on surface (where magnetic fields exit and enter Sun)q Follow an 11-year cycleq 10,000s km (Earth-sized)q Last days - monthq Can determine Sun’s rotation rate• Differential Rotation - Equator rotates more rapidly than poles (25day - 35

day)• Further proof Sun is gaseous

² Solar Flares - eruptions of charged particles and radiation


10-8

The Sun


10-9

The Sun


10-10

The Solar Interior³ The Energy source - (18th cent. View - coal, etc)

² Thermonuclear Reactions

E = mc2

c is so large that E is big even for small m! ³ Fusion in core

² Because P (3 x 1011 atm) and T (2 x 107 K) are so high, protons stick (H = 1p 1n & He = 2p 2n), so:

4 H 1 He + energy + neutrinosFor this reaction: E = 4 x 10-12 J (enough to light a 10W light bulb for

5 x 10-12 seconds!)But the Sun’s luminosity is ~ 4 x 1026 W/sec !!600 million metric tons/sec of Hydrogen is being converted into He!!!

We use models to understand what’s happening in the interior© Dr. Joseph E. Pesce, Ph.D.

FusionIn the sun: (600million tons of Hydrogen/sec =

170,000 yrs to consume mass of earth; in 10 billion years….

4 protons: (Hydrogen) + 2 electrons

p+ p+ p+ p+ e- e-

p+

p+n

n

1 helium nucleus

g-ray &

More mass before than after - mass conserved, so �extra� becomes energy (E=mc2) in the form of a photon, the g-ray.

neutrino+


© 2007-2015 Joseph E. Pesce, Ph.D.

NeutrinosNearly massless subatomic particles Produced in huge quantities during fusion and supernovae.

• Important for cosmological reasons and understanding of nuclear fusion

• Billions of them pass through every square centimeter all the time - yes, even now!

• Weakly interacting: can pass through 1 light year of lead without interacting with a lead atom!! (Luckily for us)

• Can be detected

1 light year of lead


10-13

The Solar Interior³ Hydrostatic Equilibrium

² Balance of force of gravity, which tries to squeeze Sun, and radiative pressure from fusion, which tries to blow apart Sun

³ Radiative transport² Energy transported outward by photonsHigh P, High T create High E photons (g-rays)But High P keeps them in, leading to a Random Walk -

photons collide, lose E, eventually fly free (after 106

yrs) from photosphere as visible photons


Interior of SunRadiative (= photons) +Convection

�Random walk�: g-ray to visible (Infrared)

1 million yrs

Transport of energy


The Interstellar Medium


11-2

The Interstellar Medium³ Gas and dust lying between stars (10% of the mass of our

galaxy)³ Hydrogen is the most abundant element³ Observe molecules too: H2O, CO, Ammonia,

Hydrocarbons, Amino Acids, Alcohols ³ ISM is found in different states: hot, warm, & cold


11-3

Giant Molecular Clouds³ Very cold, �dense� gas/dust clouds³ Masses ~ 106 M³ ~ 100 ly in diameter³ 74% H, 25% He, 1% other ** ** �Heavy� elements, or

�metals� = all elements heavier than H

GMCs are important because they are what stars form from

When they are compressed:

1. By cloud-to-cloud collisions

2. By supernova explosions

Star formation is initiated


11-4

Elemental Abundances


Thank You!


astro 113 week3 - Department of Physics and...

Documents

Transcript of astro 113 week3 - Department of Physics and...