Download An Introduction - Solar Physics and Space Weather

Stellar Astrophysics
An Introduction
Aug. 28, 2012
ASTR730 / CSI661
Fall 2012
Jie Zhang
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
•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
Create Radiation
•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 antineutron pairs)
•At about t = 1 second, temperature fell below 6 X 109 K,
electrons and positions annihilated to form low energy gammaray 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 Ordinary Matter
•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
Relics of primordial fireball
•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
Cosmic Microwave Background
•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
The State of the Universe
•Age: 13.7 billion years
•Composition: 73% dark energy, 23% dark matter, 4% ordinary matter
Galaxies
• This map shows 1.6 million galaxies from the 2MASS (TwoMicron All-Sky Survey) survey
• Supercluster of Galaxies lie along filaments
Galaxies
Our 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
Star Formation: Nebula
•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: Protostar
•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
•A protostar’s relatively low temperature and high luminosity
place it in the upper right region on an H-R diagram
Stars
The Sun
Solar wind
creates a big
teardropshaped
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
The Sun-Earth Connection
Credit: NASA
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
Power failure due to
March 1989 storm
Damaged transformer
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
The driver of Space Weather
Planet
Coronal mass ejections
Heliosphere: solar wind
Planet
Spiral magnetic field: radial motion of solar
wind combined with Sun’s rotation
Sprinkler
Analogy
Magnetosphere
Planet
A cometshaped
region
around the
Earth
Magnetosphere
Planet
Electric
Currents in
Magnetosphere
Magnetosphere
Planet
Energetic
particles in
Van Allen
radiation
belt
Ionosphere
Planet
Density fluctuation affects radio wave
reflection and transmission
Recent Missions
Hinode
Recent Missions
STEREO
Recent Missions
SDO
The End