ASTR730 / CSI661 Fall 2012 Jie Zhang Stellar Astrophysics An Introduction Aug. 28, 2012

The Big Bang

History of the Universe

Physical Forces Depending on temperature (T) and density (ρ)

Inflation occurs at second after the Big Bang when temperature of universe dropped to 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 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 10 9 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 10 9 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 10 9 antiprotons, there must have been 10 9 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 ( 2 H, 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 = K, f = GHz, and λ = 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 years from the center One of 200 billion stars in our Galaxy Our Galaxies

Interstellar gas and dust pervade the Galaxy Nebula: a cloud of concentrated interstellar gas and dust; 10 4 to 10 9 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

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 3 rd 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 Process It starts from an eruption from the Sun. Prediction depends on how it propagates

Space Weather: effects Aurora; Geomagnetic Storm From Space

Space Weather: effects Adverse effects Damaged transformer Power failure due to March 1989 storm

Space Weather: effects On Human Space Exploration On crew and passengers of polar-route airplanes

Space Weather: effects On Satellite Operation

Space Weather: effects On Communication and Navigation

Planet Components of Sun-Earth The driver of Space Weather Coronal mass ejections

Planet Components of Sun-Earth Heliosphere: solar wind Spiral magnetic field: radial motion of solar wind combined with Sun’s rotation Sprinkler Analogy

Planet Components of Sun-Earth MagnetosphereMagnetosphere A comet- shaped region around the Earth

Planet Components of Sun-Earth MagnetosphereMagnetosphere Electric Currents in Magneto- sphere

Planet Components of Sun-Earth MagnetosphereMagnetosphere Energetic particles in Van Allen radiation belt

Planet Components of Sun-Earth IonosphereIonosphere Density fluctuation affects radio wave reflection and transmission

Recent Missions Hinode

Recent Missions STEREO

Recent Missions SDO

The End