Oscillation (Seismology) of Sun

In left image, red is moving down, blue is moving up

Fig. 16.4

Interior of Sun

Fig. 16.5 and 16.6

The Evaporating Sun

The Sun is continually "evaporating" due to the solar wind carrying off particles from the Sun

Sun loses millions of tons of matter each second through wind

Sun has lost less than 0.1% of its mass through solar wind in its lifetime

Solar wind travels at ~500 km/s (~3 days to reach Earth)

EM radiation (light) takes 8 minutes to reach Earth from Sun

The Solar Wind

X-ray image of the Sun from the Yohkoh satellite.

The black areas, coronal holes, are regions of low density, and thus low X-ray emission, where the solar wind is able to stream out from the Sun unimpeded

Fig. 16.14

The Active Sun

The surface of the Sun is very active

Small scale activity : small jets, spicules, that last minutes - source of heat for corona?

Sunspots

Prominences

Flares

Magnetic Field

Magnetic field generates:

Solar activity, Sunspot cycle, Flares

Equator rotates faster than poles

Magnetic Field

Sunspots are pairs of cooler regions

Fig. on right, 16.18(b), is a "negative" image

Magnetic Field

22 year cycle

11 years to maximum, then 11 years to minimum

Sunspots occur within 40° of equator

Later in cycle, sunspots occur nearer to equator

Magnetic Field

Sunspot cycle is not always regular: Maunder minimum- "little ice age"

Sunspot is a region of cooler gas in photosphere surface

Prominences

Material flows along loops in magnetic field above Sun

Material does not escape Sun

Flares

Flares occur when violent explosions expel material from Sun

Coronal mass ejections

Energy Production

Fusion - 2 nuclei combine to make a larger atom.

Fission - when an atom splits into 2 smaller atoms

Annihilation- when matter and antimatter meet, both are completely destroyed and turned into energy

Every particle has an anti-particle, a particle with the same mass, but opposite properties: an electron (negative charge) has an anti-particle, the positron (positive charge)

E=mc²

Einstein's famous equation states that Energy is matter and matter is energy

Energy Production

In order of least energy to most energy, rate the following items:

Burning 1 kg of coal

Fusion of 1 kg of hydrogen

1 kg of water falling over Niagara Falls

Annihilating 1 kg of hydrogen

1 kg of TNT exploding

Energy Production

In order of least energy to most energy:

Burning 1 kg of wood

1 kg of water falling over Niagara Fall

1 kg of TNT exploding

Fusing 1 kg of hydrogen

Annihilating 1 kg of hydrogen

Sustained Energy Production

How long can 1 kg of matter power a 100 W light bulb?

Water 50 m waterfall 5 s

Coal Burning 8 h

Enriched UO₂ Fission in reactor 690 y

²³⁵ U Complete Fission 3x10⁴ y

Hot Deuterium Complete Fusion 3x10⁴ y

Matter and Complete 3x10⁷ y

Antimatter Annihilation

What Powers the Sun?

Sun outputs 4x10²⁶ W

So for the Sun:

Luminosity/Mass= 4x10²⁶ W/2x10³⁰ kg=2x10^-4 W/kg

Burning wood: 2x10² W/kg

But wood cannot burn for 4.6 billion years!

Over lifetime of Sun (4.6 billion years) Sun has output 3x10¹³ J/kg (W=J/s)

Need large amounts of energy produced constantly over billions of years

Only fusion can power Sun

Fusion in the Sun

Ionized Hydrogen (just a proton) is the main fuel source for Sun

Hydrogen is fused (converted) into Helium

First step:

Proton-proton Chain

Proton-proton chain

Where is the Energy?

Proton-proton chain: essentially 4 protons become helium-4

¹ H + ¹ H --> ² H + positron + neutrino

Neutrino is an almost massless particle that barely interacts with matter

² H + ¹ H --> ³ He + energy

³ He + ³ He --> ³ He + ¹ H + ¹ H + energy

Energy is released in gamma ray radiation

Net reaction is: 4(¹ H) --> ⁴ He + energy + 2 neutrinos

Where is the Energy?

Proton-proton chain: essentially 4 protons become helium-4

Energy is released in gamma ray radiation

Net reaction is: 4(¹ H) --> ⁴ He + energy + 2 neutrinos

Energy comes from the difference in the mass of 4 protons and helium-4

Energy is Mass

Mass of 4 protons = M (4p) = 4( mass of a proton)

= 4(1.672630x10^-27 kg) = 6.6943x10^-27 kg

Mass of helium-4 = 6.6466x10^-27 kg

M (4p)-mass (⁴ He) = 0.048x10^-27 kg

E = mc² = 0.048x10^-27 kg (3x10⁸ m/s)² = 4.3x10^-12 J

J=kg m/s²

1kg --> 6.4x10¹⁴ J

Solar Neutrino "Problem"

Only way to directly confirm fusion in Sun is to measure neutrinos, which directly escape Sun

Neutrinos are hard to detect

On Earth we detect fewer neutrinos than predicted

Reason: neutrinos have a small mass and some change into different types before they reach Earth

We now have good evidence this summer that neutrinos can change