ASTR730 / CSI661 Fall 2012 Jie Zhang

Stellar Astrophysics

An Introduction

Aug. 28, 2012

The Big Bang

http://rampant-mac.com/dp_07/Big-Bang-Theory_alt2_1920.jpg

History of the Universe

http://www.negotiationlawblog.com/Big%20Bang.jpg

Physical Forces

Depending on temperature (T) and density (ρ)

•Inflation occurs at 10-35 second after the Big Bang when temperature of universe dropped to 1027 K; at this temperature, strong force became distinct from the electromagnetic-weak force

•Before the inflation, the space is “empty”, filled with only virtual particles dictated by quantum mechanics

•Matter and energy of the universe is created during the inflation

•Just after the inflationary epoch, the universe was filled with particles, antiparticles and energetic gamma-ray photons

Inflation

•At t=10-6 second, the temperature in the universe dropped to the threshold temperature of 1013 K, at which the photons can not produce proton and anti-proton pairs (and neutron and anti-neutron pairs)•At about t = 1 second, temperature fell below 6 X 109 K, electrons and positions annihilated to form low energy gamma-ray photons that can not reverse the process•As a result, matter and anti-matter content decreased, and radiation content increased•From 1 second to 380,000 years, the universe is dominated by the radiation (so called primordial fireball) derived from the annihilation of particles and antiparticles created early by the inflation

Create Radiation

•If there had been perfect symmetry between particles and antiparticles, every particles would have been annihilated, leaving no matter at all in the universe•There are 109 photons in the microwave background for each proton/neutron in the universe•Therefore, there is a slight but important asymmetry between matter and antimatter•Right after the inflation, for every 109 antiprotons, there must have been 109 plus one ordinary protons, leaving one surviving after annihilation

Create Ordinary Matter

•When the universe was 3 minutes older, the temperature was low enough to pass the deuterium (2H, one proton + one neutron) bottleneck to further produce helium

•At 15 minutes, the temperature of the universe is too low for any further nucleosynthesis

•Therefore, the relics of primordial fireball are hydrogen, helium (1 helium out of every 10 protons), and photons (1 billion photons for every proton)

•Heavier elements are formed later in the stars, not in the early universe

Relics of primordial fireball

•Recombination: at 377,000 years (T = 3000 K) after the Big Band, hydrogen (and helium) nuclei started to capture electrons to form neutral hydrogen (and helium) atoms. The photon’s mean free path becomes effectively infinite•As a result of recombination, the universe has become transparent. This cosmic event is also called “decoupling”•Cosmic Microwave Background (CMB): the photons present at the time of decoupling are the same photons that we see in CMB. Therefore, CMB is a picture of the universe at the end of recombination epoch.•CMB is observed as a spectrum of uniform black body thermal emission form all parts of the sky: T = 2.725 K, f = 160.2 GHz, and λ = 1.873 mm

Cosmic Microwave Background

•Age: 13.7 billion years•Composition: 73% dark energy, 23% dark matter, 4% ordinary matter

The State of the Universe

Galaxies

• This map shows 1.6 million galaxies from the 2MASS (Two-Micron All-Sky Survey) survey

• Supercluster of Galaxies lie along filaments

Galaxies

We are located in the middle of the Milky Way Galaxy

28,000 light yearsfrom the center

One of 200 billionstars in our Galaxy

Our Galaxies

•Interstellar gas and dust pervade the Galaxy •Nebula: a cloud of concentrated interstellar gas and dust; 104 to 109 particles per cubic centimeter

Star Formation: Nebula

•Protostar: the clump formed from dense and cold nebula under gravitational contraction

•The protostar contracts, because the pressure inside is too low to support all the mass.

•As a protostar grows by the gravitational accretion of gases, Kelvin-Helmholtz contraction causes it to heat and begin glowing

•When its core temperatures become high enough to ignite steady hydrogen burning, it becomes a main sequence star

Star Formation: Protostar

Star Formation: Protostar

•A protostar’s relatively low temperature and high luminosity place it in the upper right region on an H-R diagram

Star Formation

Stars

The Sun

Solar wind creates a big teardrop-shaped heliosphere around the solar system, by interacting with the interstellar wind

The Earth The Earth

3rd planet from the Sun

1 AU = 150 million km

Travel time:By light --8 minutes

By Solar Wind-- ~ 100 hrs

Credit: NASA

The Sun-Earth Connection

Space Weather: the ProcessSpace Weather: the ProcessSpace Weather: the ProcessSpace Weather: the Process

It starts from an eruption from the Sun.

Prediction depends on how it propagates

Space Weather: effectsSpace Weather: effectsSpace Weather: effectsSpace Weather: effects

Aurora; Geomagnetic Storm

From Space

Space Weather: effectsSpace Weather: effectsSpace Weather: effectsSpace Weather: effects

Adverse effects

Damaged transformer

Power failure due to March 1989 storm

Space Weather: effectsSpace Weather: effectsSpace Weather: effectsSpace Weather: effects

On Human Space Exploration

On crew and passengers of polar-route airplanes

Space Weather: effectsSpace Weather: effectsSpace Weather: effectsSpace Weather: effects

On Satellite Operation

Space Weather: effectsSpace Weather: effectsSpace Weather: effectsSpace Weather: effects

On Communication and Navigation

Planet

The driver of Space WeatherThe driver of Space WeatherThe driver of Space WeatherThe driver of Space Weather

Coronal mass ejections

Planet

Heliosphere: solar windHeliosphere: solar windHeliosphere: solar windHeliosphere: solar wind

Spiral magnetic field: radial motion of solar wind combined with Sun’s rotation

Sprinkler Analogy

Planet

MagnetosphereMagnetosphereMagnetosphereMagnetosphere

A comet-shaped region around the Earth

Planet

MagnetosphereMagnetosphereMagnetosphereMagnetosphere

Electric Currents in Magneto-sphere

Planet

MagnetosphereMagnetosphereMagnetosphereMagnetosphere

Energetic particles in Van Allen radiation belt

Planet

IonosphereIonosphereIonosphereIonosphere

Density fluctuation affects radio wave reflection and transmission

Recent Missions

Hinode

Recent Missions

STEREO

Recent Missions

SDO

The End