Stellar Evolution study guide

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Stellar Evolution study guide

Stellar Evolution
Star Formation

A Protostar is formed from a nebula that collapses due to the force of gravity
Fusion reactions begin and a new star is formed

Life Cycle of a Star: already determined due to the amount of mass it began with.

Protostar turns into a medium size star
Medium sized star becomes a red giant with all of its matter squeezed together.

It could do two things depending on its mass

Red Giant with low mass becomes a white dwarf (shines with a white hot light) it then becomes a black dwarf (dead star)

If the Red Giant was very massive it can become a supernova and blow up, its core can become a neutron star (gives off pulses of energy) or a Black hole

Black Holes

Begin as stars with mass 10x greater than our sun
Have a short life span due to this mass
After the supernova explosion the core that remains is so massive that (without fusion to support it) the core is swallowed by its own gravity
Not even light can escape it, it swallows energy and matter like a vacuum cleaner
Most are found due to their companion star, gases from the companion are pulled into the black hole and they give off a burst of x-rays before the matter falls into the black hole.
There are new theories on black holes, hole to new universe, form new stars?

Hertzsprung-Russell diagram

The properties of mass, luminosity, temperature, color and diameter are closely related
Each star has specific characteristics related to each of the properties
90% of all stars fall along main sequence

Basic Properties of Stars

Magnitude: is how bright a star appears
Apparent Magnitude: Brightness of a star as it appears on Earth
Absolute magnitude: Amount of light a star actually gives off
Luminosity: is the actual energy output on the surface of a star per second, measured in watts
Positions and Distances of Stars
Distance is measured in light years (distance light travels in 1 year)
To account for the motion of the Earth when viewing the stars, the apparent shift in position of the star is called parallax

Telescope Types

Refracting: first type, lenses brought visible light top a focus
Reflecting: mirrors bring visible light to a focus

All telescopes goals are to bring radiation (wavelengths human eye can not detect) to a focus

There are x-ray, infrared, ultraviolet, and gamma ray telescopes that only detect those parts of the electromagnetic spectrum
Interferometry: process of linking separate telescopes together so they act as one. Very detailed!

Space based telescopes: Hubble, Ultraviolet Spectroscopic Explorer, Chandra X-Ray

Spectra

Spectrum: Visible light arranged according to wavelength, used to find what elements stars are composed of.
Continuous: can be caused by a glowing gas or liquid
Emission: bright lines at certain wavelengths

Absorption: caused by different chemical elements

Groups of Stars

There are 88 constellations that were named by ancient people
They appear to move around the poles
They can be seen only during certain times of the year.
They are not gravitationally bound together

Binaries

Two stars that are gravitationally bound together
Orbit a common center of mass
Most appear as a single star

Novas

Nova is a star that increases in brightness in a few hours

Remember the Solar Composition

74% hydrogen
26% helium
Most of the universe has the same composition
Fusion is the energy maker of the sun

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