Astrophysics Notes

Topics: Star, Sun, Supernova Pages: 8 (1154 words) Published: March 1, 2013

Galaxy = collection of large number of stars, mutually attracting each other through the gravitational force and staying together

No. Of stars varies between a few million and hundreds of billions. There are approximately 100bn galaxies in the universe

3 types of galaxies:
1. Spiral (Milky Way)
2. Elliptical (M49)
3. Irregular (Magellanic Clouds) – Anything that is not elliptical or spiral = irregular. No specific structure, Large and small Magellanic clouds are the nearest to irregular galaxies.

Why is there a black hole?
Not enough evidence to support it but is widely believed to be true. – Cant see it but not a hole, gravitational force = so strong you cant see it, hence an absence of light = black hole (even though its technically not a hole).

Polaris = North Star


Stars = Fusion reactors of gases. (Hydrogen + Helium) Them fusing = chain effect.

Interstellar dust coming together through mutual gravitational attraction

Nebulae = Dying star after its gone supernova./Cloud of gas and dust in space.

Nuclear Fusion = Very high temps are needed in order to begin the fusion process, 107K.

Star = Big ball of gas with fusion going on at the center held together by gravity

There are variations between stars, but by and large they’re really pretty simple.

Mass of star dictates its luminosity and temperature.

Gravity pulls outer layers in - Gas Pressure pushes them out

The more mass a star has = more central pressure

Luminosity of a star is the energy that it releases per second. Sun has a luminosity of 3.9×1026 J/s The energy that arrives at the earth is only, a very small amount when compared to the total energy released by the sun. Luminosity = Power

Distance travelled by the sun = d = 1.5 × 1011m

Average distance from earth to the sun = distance from earth to the sun.

Estimate how much energy falls on a surface of 1m2 in a year

3.9×1026W4πd2 = 1378.1W/m-2 = 1378.1 ×(60×60×24×365.25) =…

Black body radiation:

Black body - perfect emitter

Clear relationship between the temperature of an object and the wavelength for which the emission is maximum those relationships are known as Wien’s law:

λmaxT= 2.9 × 10-3

Hottest suns = violet colors NOT RED.

L= σAT4

Boltzmann curve should be smooth. Is not, wavelengths tell us the composition of the star. Absorption + Emission spectra and thus figure it out.

Red Giants

Large, cool stars with reddish appearance; all main sequence stars evolve into a red giant. In red giants there are nuclear reactions involving the fusion of helium into heaver elements.

2 kinds:
Red Giants + Red Super Giants (Super giants = 2AU in diameter)

AU = distance from earth to sun.

Later stage of life

White dwarf:

Very hot star, early stage of stars life

Neutron star:

Mainly made up of helium.

Plasma = Superheated gas. Can no longer remain attached to the nucleus.

Electrons are so excited; they plow into the protons of the element and for neutrons. And become plasma.


Pulsars are highly magnetized rotating neutron stars, which emit a beam of detectable electromagnetic radiation in the form of radio waves. Periods of rotation vary from a few milliseconds to seconds.


Is a stellar explosion that creates an extremely luminous object. The explosion expels much or all of a stars material at a velocity of up to a tenth the speed of light, driving a shock wave into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant.

Creates a shock wave that ripples through space.

Causes a burst of radiation that may briefly outshine its entire host galaxy

Black Holes:

Region of space where nothing can escape its gravitational field, the G field is so powerful that nothing can escape. The name comes from the fact that electromagnetic radiation is...
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