Formation of Stars and our Solar System

Formation of Stars

and our Solar

System

• 1st Step:

– The birth of a star starts in a large cloud of

gas and dust called a nebula.

– Gas and dust begin to

collide and stick together

because of gravity.

• 2nd Step:

– As nebula contracts and heats up, a small

star is formed called a protostar.

– Eventually, the protostar will

begin nuclear fusion which

is hydrogen combining with

other hydrogen to form helium.

• 3rd Step:

– Star joins the main sequence which is a

chart that maps out brightness vs.

surface temperature. The mass of the

star also determines where it will end up.

– A star will spend 90% of its life here on the

main sequence until it begins to run out

of hydrogen.

Main Sequence Stars

• A major grouping of stars that forms a

narrow band from the upper left to the

lower right when plotted according to

luminosity and surface temperature on

the Hertzsprung-Russell diagram

Types of Stars Classification

Class Temperature Color

O 20,000- 60,000 K Blue

B 10,000 – 30,000 K Blue-white

A 7,500 – 10,000 K White

F 6,000 – 7,500 K Yellow-white

G 5,000 – 6,000 K Yellow

K 3,500 – 5,000 K Orange

M 2,000 – 3,500 K Red

Hertzsprung-Russell Diagram Hot &

bright

Cold &

bright

Cold &

dim

Hot &

dim

• Beginning of the End:

– Stars begin to die when they run out of

hydrogen and gravity starts shrinking the core.

– The outer core of hydrogen begins to fuse and

the star size expands

and cools down as it

moves away from the

core. This produces a

red giant.

• Beginning of the End:

– Eventually, star can fuse helium into other

elements like carbon, oxygen, and other heavier

elements. During this time, it is called a

planetary nebula.

– The heaviest element that can be

formed in a red giant is iron. Any

element heavier than iron is made

during an explosion of a red supergiant.

• Beginning of the End: (Low mass stars)

– Once the star runs out of “fuel”, the star shrinks

under its own gravity.

– Low mass stars like our sun

turn eventually into a hot, dim

white dwarf

• Death of Stars: Low and Medium Mass

Red Giant

Main Sequence Star

Planetary Nebula

White Dwarf

• Beginning of the End: (High mass stars)

– Stars with high masses will turn into red

supergiants and eventually go supernova.

– During a supernova, the star becomes brighter

than the entire galaxy it is in.

– High mass stars either become

neutron stars or black holes

depending on their mass.

• High Mass Stars:

– Mass greater than 8x our sun create elements

larger than iron when they explode.

– A Neutron star is formed if the remaining star is

< 3 times the sun’s mass.

– Black Holes form if the remaining star is

>3 times the sun’s mass.

• Death of Stars: High Mass

Red Super Giant

Main Sequence Star

Supernova

Neutron Star Black Hole

• What is a Black Hole?

– An object so massive and dense that

not even light can escape its gravity.

– The end result from a supernova of a

star that has a mass greater than 3x

the sun.

• What is a Neutron Star?

– Neutron stars are tiny, dense, rapidly rotating

stars that can bend light around it.

– Some neutron stars rotate

very rapidly and emit

beams of electromagnetic

radiation as pulsars.

Life Cycle of Stars

Expanding Universe

In the mid-1920’s a man by

the name of Edwin Hubble

studied many galaxies to

figure out if the galaxies are

moving towards us or away

from us.

Hubble guiding the Hooker 100 inch telescope in 1923.

Doppler Effect

He decided to

use the Doppler

Effect to look at the

color of the light

coming to us from

the distant galaxies.

The Hooker 100 inch telescope atop Mt. Wilson near Pasadena, CA. It was the largest telescope in the world from 1917-1947.

Red Shift What he found was that all galaxies were

moving away from us and the farther galaxies

were moving faster than the close galaxies.

This phenomenon is called Hubble’s Law.

Big Bang Theory

The only way Hubble could explain how all

the galaxies are moving away from us was to

say that at one time, all the galaxies were

together in one hot, tiny space.

Then there was a great explosion and all the

matter started to expand and move away from

each other.

This became the Big Bang Theory!

To understand the Big

Bang just imagine that the

galaxies are located on the

surface of an inflating balloon.

As the balloon expands,

every point on its surface is

moving away from every other

point.

So what can we learn from the light from stars?

We can tell that they are moving away from us and that the

universe is expanding.

We can calculate the speed of that expansion and can infer

the age of the universe (12 billion years).

All this just from starlight!