Astronomy 1020 Stellar Astronomy Spring_2016 Day-25

Course Announcements Apr. 1 – Last day to drop a class with W, F, FA Remaining Observing nights: Dark – Thurs. 3/31, the observatory Dark – Tues. 4/5, the observatory 1 st Q – Wed. 4/13, 7:30pm on campus Observing Reports are due: Mon. 4/18 at class time. Exam-3 target, Monday 4/4 No class Friday – Good Friday

Astronomy in the Fall 2016 ASTR-1010/ Planetary Astronomy + Lab (H,R) ASTR Problems in Planet Astronomy* ASTR-1020/ Stellar Astronomy + Lab (R) ASTR Intro. to Observational Astronomy ASTR-3005/3006 – Observational Astronomy & Lab ASTR-4010 – Stellar Astrophysics (seniors only, independent study) PHYS-3250 – Topics in Relativity PHYS-3701 – Advanced Lab (Astronomy this semester) * Now required to get Honors credit

The Sun

The Sun is the Largest Object in the Solar System The Sun contains more than 99.85% of the total mass of the solar system If you put all the planets in the solar system, they would not fill up the volume of the Sun 110 Earths or 10 Jupiters fit across the diameter of the Sun How big is the Sun?

APSU-Feb2016 Stellar Interiors: Solar-Type Stars Dr. David James, CTIO ARCoIRIS Project Scientist Dark Energy Camera Scientist

How Do You Describe a Stable, Main Sequence Star? 4 Structure Equations: d M /dr = 4  r 2  dP/dr = G M  /r 2 dT/dr = -3  L /  r 2  T 3 (rad) dT/dr = 0.4(T/P)dP/dr (conv) d L /dr = 4  r 2  4 Auxiliary Equations: P =  kT/  m H (IGL) P = k   (AGL)  =  0 Z(1 + X)  T -3.5 (opacity)  =  0 X 1 X 2  T (Energy gen.) = ~4 (pp); ~20 (CNO)

How Do You Describe a Stable, Main Sequence Star? Loosely: A self-gravitating sphere of mostly Hydrogen (74%) and Helium (24%) in hydrostatic equilibrium with the inward gravitational force balanced by an outward radiation pressure, powered by Hydrogen fusion in the core.

Structure of the Sun We only see the outer layers of the Sun. Physics tells us about the interior. Key idea: hydrostatic equilibrium. At each point there’s a balance: Outward pressure = inward force of gravity. Rate of energy emitted = rate produced in the core. Density, temperature, pressure increase towards the center.

Interior of the Sun

 We only see the outer layers of the Sun.  Physics tells us about the interior.  The Sun must be in balance to have existed in a constant state for billions of years.

 At each point in the Sun there is balance:  Hydrostatic equilibrium: outward pressure = inward force of gravity.  Solar energy production must equal what is radiated away.

 Density, temperature, and pressure increase toward the center  creating the necessary conditions for nuclear fusion.

Atomic Nuclei Nuclei consist of protons and neutrons. Protons: positive electrical charge. Neutrons: no electrical charge. Electrical forces push protons apart. The strong nuclear force binds protons together. Fusion requires ramming protons together at high speed (i.e., at high temperature).

Isotopes of Hydrogen and Helium Number of protons sets the type of atom. Isotopes: Number of neutrons can vary. Hydrogen (H): one proton. Ordinary H: no neutrons ( 1 H). Deuterium: one proton, one neutron ( 2 H). Helium (He): two protons. Ordinary helium: two protons, two neutrons ( 4 He). Helium-3: two protons, one neutron ( 3 He).

The Periodic Table

 Nuclear fusion involves the fusing of atomic nuclei.  Nuclei consist of protons and neutrons.  Protons: positive electrical charge.  Neutrons: no electrical charge.  Electrical forces push protons apart.

 The strong nuclear force binds protons and neutrons together.  Fusion requires ramming protons together at high speed (i.e., at high temperature).  Creates more massive nuclei from less massive ones.

Powering the Sun  The Sun has existed for about 4.6 billion years.  The Sun must therefore generate a lot of energy over a long time.  Source: fusion of hydrogen into helium in the central core.  This fusion is often called hydrogen burning.  All main sequence stars are powered by the fusion of hydrogen into helium, which generates energy.

Fusion and Energy  Mass of four hydrogen (H) nuclei is times greater than 1 helium (He) nucleus.  Relativity: mass and energy are equivalent: E = mc 2 or m = E/c 2  Difference in mass is released as energy in this very efficient process.  Fusion takes place in the core, where it is hot enough (15 million K).  Fusion process in the Sun: proton-proton chain.

Testing Models of the Sun Hydrogen fusion emits neutrinos. Neutrinos: light atomic particles, no charge. Very weak interactions with matter. Can measure the rate they arrive at Earth. Rate agrees with predictions and with experiments on neutrino physics.

Solar Neutrinos

 Hydrogen fusion emits neutrinos: light atomic particles, no charge.  Very weak interactions with matter.  Should escape the core freely.

 Can measure the rate and types that arrive at Earth (they can change flavors).  Rate agrees with predictions and with experiments on neutrino physics.

 Neutrino detectors are atypical telescopes.  Today they use vast quantities of ice or ultra- pure water: Scientists wait for neutrinos to interact, generating a detectable signal. CONNECTIONS 14.2