Astrophysics lecture

By
Ahmed Haider Ahmed
B.Sc. Physics 2011

 In physics we use centimeter to measure length and
states of matter is three at ordinary conditions (solid,
liquid and gas).
 In astrophysics we use light year (1 light year = 9.46 x 1012 km)
and the matter often is plasma (ionized gases).
 Look at the difference of scales between physics and astrophysics
in this table:Measurement of cm in atomic physics Measurement of cm in astrophysics
10-8
10-16
10-24
diameter of atom
diameter of the nucleus of H
effective cross section radius
of 1 MeV neutrinos
108
1016
1024
Diameter of moon
Diameter of solar system
distance of nearest
neighboor Megllanic cloud

 In astrophysics the state often is plasma (ionized gases) and this
produce new branch of physics that called plasma physics which could
solve the problems that faced the astronomers.
 Note : The astronomers who develop plasma physics.
 The astronomer used the plasma physics to solve the
following mean problems:
1. Experiments of nuclear fusion.
2. Explain the irregular motion inside stars.
3. Interpretation of atmosphere surrounding stars like Solar Corona.
4. Give interpretation for flow rate of matter from stars to space that
known as solar wind.
5. Explain how star forming.

 The most important phenomenon that plasma
physics explained is how stars forming:
If a cool cloud of dense molecular gas surrounding by hot gas ,
the cool one will compress or contract reaching to stage of
gravitational collapse , and this is the starting of forming
stellar clusters (stars) or galaxies clusters and this is the
natural method of forming stars.
 So, we can say that :
The universe is renewable continuously , stars die and
stars born continuously.

 Galaxies is the massive units of universe
consist of billions of objects (Nebulae –
Stars – Planets – Asteroids – Comets – Dust
– Gases) orbit each others and controlled
by gravity making them in one unit.
 Galaxies is the place of birth and death of
stars.
 Galaxies move away each other with high
velocities.

Largest ever galaxy portrait –
stunning HD image of Pinwheel Galaxy

 The star evolves during millions of years,
passing through various stages of
development, but the disaster is possible
and every thing will change in few days
like that happen in supernovae of large
stars when it has sudden death without
passes through red giants.
Look at the following picture :

 Supernovae explosion is the sudden death of a large star
without passes through red giants.
 The light from a supernova explosion is brighter than that
from an entire galaxy consisting of billions of stars and we
can see it on earth by naked eye. When the explosion is
terminated, the star is considered to have died; most of its
mass is scattered into space and the left-over material is
very condensed and does not shine like the other stars.
 The famous supernovae happened in year 1054 A.C in Taurus
and its ruins still exist that called crab nebula.
‫عام‬ ‫شوهدت‬ ‫سوبرنوفا‬ ‫اشهر‬1054‫االن‬ ‫اثارها‬ ‫على‬ ‫ويطلق‬ ‫الثور‬ ‫برج‬ ‫في‬ ‫م‬
‫السرطان‬ ‫سديم‬

 If the mass of star reaches to 1.4 of sun mass or more. Then
this star will vanish suddenly without passes through White
dwarfs i.e. may be supernovae.
 Mechanism of explosion
Nuclear reaction inside star produce iron at temperature
reaches to two billions Co and this produce neutrons with
huge energy to outer space then the star contract to
substitute the decreasing that happened and this cause
raising the temperature in range 4 – 6 billion Co in a few
weeks and every thing is collapsed , when temperature
reaches to 7 billion Co the reverse process happen and energy
absorbing and then the atmosphere of star goes inside it
under its gravity at this time the exhaustible nuclear energy
explode out suddenly by its powerful force.

After talking about some fundamentals of
astrophysics, I’d talk about the topic that won
Noble prize for physics this year 2011 , the
accelerating universe exactly (the discovery of the
accelerating expansion of the Universe through
observations of distant supernovae)

 In the past scientists thought that universe is static.
 Even Einstein set cosmological constant in general
relativity.
 In 1929 Edwin Hubble discovered that the galaxies move
away from us i.e. the universe is not static it is expanding
and set Hubble law that calculate the velocity of galaxies:
V = Ho d
 where v is the galaxy's radial outward velocity, d is the
galaxy's distance from earth, and H is the Hubble constant.
 Einstein describe the cosmological constant as the great
mistake.

 We can understand it using properties of waves
and Doppler effect.
 For example if star move away from the earth
this called redshifted
 if spaceship move towards from star this called
blueshifted.
 Nowadays , scientist discover that the universe
is not only expanding but also it accelerates.

 SAUL PERLMUTTER (Nobel winner 2011) showed the
possibility of separating the relative
contributions of the mass density and the
cosmological constant to changes in the
expansion rate by studying supernovae at a
range of redshifts.
 ADAM G. RIESS and BRIAN P. SCHMIDT (Nobel winners
2011) make evidence for accelerating universe
using spectroscopy techniques and estimate the
dynamical age of the universe to be 14.2± 1.7
Gyr.

 Some points I avoid mentioned it :
 Types of supernovae.
 Details of star lifecycle.
 Spectroscopy concepts and details of
research that won Nobel prize.
This to make lecture acceptable for any one
Ahmed Haider

1. The Fourth State of Matter (An Introduction to Plasma Science) 2nd
Edition , Shalom Eliezer and Yaffa Eliezer.
2. Universe and black holes , R.W.
3. http://www.spacetelescope.org
4. MEASUREMENTS OF Ω AND Λ FROM 42 HIGH-REDSHIFT SUPERNOVAE ,
S.PERLMUTTER, AND OTHERS ,THE ASTROPHYSICAL JOURNAL , 1999
June 1
5. OBSERVATIONAL EVIDENCE FROM SUPERNOVAE FOR AN ACCELERATING
UNIVERSE AND A COSMOLOGICAL CONSTANT,
ADAM G. RIESS,1 ALEXEI V. FILIPPENKO,1 PETER CHALLIS,2 ALEJANDRO
CLOCCHIATTI,3 ALAN DIERCKS, PETER M. GARNAVICH, RON L.
GILLILAND,5 CRAIG J. HOGAN,4 SAURABH JHA, ROBERT P. KIRSHNER,B.
LEIBUNDGUT, M. M. PHILLIPS, DAVID REISS,4 BRIAN P. SCHMIDT,8,9
ROBERT A. SCHOMMER, R. CHRIS SMITH,7,10 J. SPYROMILIO,6
CHRISTOPHER STUBBS,4NICHOLAS B. SUNTZEFF,7 AND JOHN TONRY11
Received 1998 March 13; revised 1998 May 6
Ahmed Haider

Astrophysics lecture

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Astrophysics lecture