Introduction to

AstrophysicsRonald L. Westra

Department Mathematics

Maastricht University

Introduction to

Astrophysics

1.

Astronomic Scales in Space and Time

Earth Sun Jupiter.

Galaxy M31, known as the Andromeda nebula

Collection of galaxies. The three fuzzy galaxies left merging, The crisp galaxy in the center is on the background

Large-scale map of the observable universe showing the the largest structures visible in the universe.

Each point in this diagram represents one single galaxy

The Universe at the young age of 300,000 years. The colors represent temperature fluctuations in the Cosmic Background Radiation

Wilkinson Microwave Anisotropy Probe

Subtle variations in the CBR.

The Giant Impact Theory suggests that a Mars-sized object crashed into the early Earth. Most of the debris thrown into space fell back on Earth, but a fraction aggregated into the Moon. This theory is supported by the similar composition of rocks on the Earth and Moon.

2.

Stellar Evolution

Some characteristics of the sun

radius (R) 7 1010 cm

mass (M) 2 1033 g

mean density () 1.4 g/cm3

total energy output (L) 3.82.1026 Joule/sec

age 1.5 1017 sec

core temperature 5 106 K

surface temperature 5 103 K

distance to earth 1.5 1013 cm

MeV7.26e2HeH4 01

42

11

Nuclear fusion in centre of sun

O – B – A – F – G –

K – M – R – N – S

Spectral Types

Absolute and Relative Luminosity

24 r

Lrel

absL

Original Hertzsprung-Russell Diagram ( HRD)

Binding energy per nucleon as function of mass number A.

Glowing gaseous streamers of an extinct titanic supernova explosion of a massive star

in Cassiopeia A (Cas A)

Composite image of the Crab Nebula

showing superimposed images of X-ray (blue) (by Chandra X-ray space telescope), and optical (red) (by the Hubble space telescope).

First published registration of a pulsar, Hewish et al., Nature 217, p. 710, 1968.

Path of the stellar evolution of a main sequence star of one solar mass in the Hertzsprung-Russell diagram

log Teff in K

log L/ L

sun

L/ L

surface temperature (K)

The HRD for 10 stellar clusters. At right ordinate the age in billion years of the bifurcation point from the main sequence.

Abundances of chemical elements in the neighbourhood of our sun. The marks are from the intensities from spectral absorption lines in the sun’s atmosphere, the lines from meteorite and terrestrial data.

An example of an unstable – but not-periodic – star is this massive ‘Wolf-Rayet star’ NGC2359, that irregularly ejects large parts of its own outer envelope in gargantuan explosions. The star itself is in the central bubble, the clouds are remnants of previous ejections.

main sequence

RR Lyrae

Cepheids

instability strip

surface temperature

Luminosity

Variable stars in the HRD. Pulsating variable stars are found in the instability strip connecting the main sequence and the red-giant region.

long period variables

0 20 40 60 80 1002.5

3

3.5

4

4.5

5Cepheid Luminosity-Period Law

Period [days]

log

(L/L

sun

)

Relation between luminosity and oscillation period for Cepheid type 1 variable stars.

Ronald L. Westra

Systems Theory Group

Department Mathematics

Maastricht University

Westra@math.unimaas.nl