Star Life Cycles

The Sun/Life Cycle of Star

Learning Objectives:
PS.U.3c - Stars form from clouds of dust and gas.
PS.U.3b - The mass of a star determines what a star will be like.
PS.U.3.a - Be able to match the mass of a star with it's life cycle.

There are three types of galaxies, Spiral, Irregular, and Elliptical. What shape is our galaxy?

Our galaxy, the Milky Way galaxy, is a spiral galaxy that looks somewhat like a pinwheel.

The Life Cycle of a Star

• All stars begin life as dust in a nebula.

• Gravity begins to form masses of hydrogen in the nebula.

• When the heat in the protostar reaches 15,000,000 C, nuclear fusion starts and a star is born!

This is the Pillars of Creation within the Eagle Nebula, part of M16, viewed by the Hubble Telescope

Beginning of a Star

• Stars form in a cloud of dust and gas called a Nebula

• Gravity begins to pull the dust and gas into a ball

• The temperature gets hotter as hydrogen and helium form releasing a bunch of energy

• By the end of this, the ball of particles and energy officially becomes a star

Multiple Choice

Stars form in a cloud of dust and gas which is called a _______

• chromosome

• stellar

• photosphere

• nebula

Stars and the HR Diagram

• The HR Diagram is a graph that compares the surface temperature of a star with its magnitude or how bright the would be if they were all the same distance from Earth.

• Luminosity is a term that measures how much energy leaves a star in a certain period of time.

• General Rule: As luminosity increases, brightness increases.

What do the axes on this chart show us about stars?

Temperature

Luminosity

Spectral Class

Magnitude

What affects luminosity?

• Temperature: As temperature increases, luminosity increases.

• Size: As size increases, luminosity increases.

• Most Luminous? Large and Hot

• Least Luminous? Small and Cool

Multiple Choice

What is the approximate surface temeprature of the sun according to the HR diagram?

• 5,500 K

• 6,000K

• 7,200 K

• 15,000K

Multiple Choice

Would the surface temperature of a red supergiant be higher or lower than a white dwarf?

• Higher

• Lower

Multiple Choice

What is the color of the stars with the highest surface temperature?

• Red

• Yellow

• White

• Blue

Multiple Choice

Most of the stars on the HR diagram are classified as which type of star?

• White Dwarfs

• Main Sequence

• Giants

• Supergiants

Multiple Choice

Star A has a surface temperature of 10,000K and medium brightness. What color is it?

• White

• Red

• Yellow

• Blue

Multiple Choice

What kind of star is Sirius, the Dog Star?

• Main Sequence

• White Dwarf

• Blue Giant

• Red Supergiant

2 Pathways:

The mass of the star that forms in the nebula determines how the star will burn fuel:

--small stars burn their fuel more slowly and reach lower temperatures.

--large stars burn through their fuel rapidly and reach higher temperatures.

Common Ground:

All Stars begin life as a H -> He fusing Main Sequence star.

No matter the mass of a star, as its hydrogen supply begins to run low, the core cools and the star takes on a red color, forming either a Red Supergiant or a Red Giant.

Different Endings:

Large stars can end up as black holes or pulsars.

Small stars can end up as a Nova, Supernova or a Black Dwarf.