LECTURE ON : ASTROPHYSICS,

ACCELERATING UNIVERSE

By

Ahmed Haider Ahmed

B.Sc. Physics 2011

To

My sisters

Dedication

Ahmed Haider

FROM PHYSICS TO ASTROPHYSICS

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 atomdiameter of the nucleus of Heffective cross section radius of 1 MeV neutrinos

108 1016 1024

Diameter of moon Diameter of solar system distance of nearest neighboor Megllanic cloud

ASTROPHYSICS STATE OF MATTER

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.

FORMING OF STARS

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.

star birth in a galaxy

GALAXIES

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

LIFECYCLE OF STARS

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 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 االن 1054اشهر اثارها على ويطلق الثور برج في مالسرطان سديم

Crab Nebula

WHY IS SUPERNOVAE HAPPEN?

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.

Supernovae in NGC 2397 galaxy

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)

THE DISCOVERY OF EXPANDING UNIVERSE

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.

THE DISCOVERY OF EXPANDING UNIVERSE

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.

ACCELERATING UNIVERSE 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.

NOTES ABOUT THIS LECTURE 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

REFERRENCES 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