studying the lives of stars stars don’t last forever each star is born, goes through its life...

Studying the Lives of Stars Stars don’t last forever Each star is born, goes through its life cycle,

and eventually die

Life Cycle of a Star

A Star is Born

A star is made up of a large amount of gas in a relatively small volume

A nebula, is a large amount of gas and dust spread out in in an immense volume

All stars begin their lives as parts of nebulas

Gravity can pull some of the gas and dust in a nebula together and it begins to spin – this is called a stellar nebulla

The contracting cloud is then called a protostar

Protostar – The Earliest Stage A protostar is the earliest stage of a star’s life

A protostar is born when the contracting gas and dust become so hot that nuclear fusion starts

Main Sequence

Once nuclear fusion occurs in the cloud, it will begin to glow brightly

It contracts a little and becomes stable

It is now a main sequence star and shines as nuclear fusion produces heat and light

The star may remain in this stage for millions or billions of years

Red Giant As the main sequence star

glows, hydrogen is converted to helium

When the hydrogen supply begins to run out, the core becomes unstable and contracts

The outer shell starts to expands and glows red as it cools

It is now a red giant Red Giant – expands and glows red as it cools

The outer shell begins to expand, cools, and glows red

Red Super Giant

Medium vs. Massive Stars The amount of mass a star has determines

the path it will take after the red giant phase

Medium Stars – Planetary Nebula At 200,000,000 °C the helium atoms in the core fuse to

form carbon atoms

The last of the hydrogen gas in the outer shell is blown away to form a ring around the core

The ring is a planetary nebula

White Dwarf When all the helium atoms are fused,

the star begins to die In white dwarfs, gravity causes the last of the star’s matter

to collapse inward and compact

It is now a white dwarf

The star’s matter is extremely dense

White dwarfs are the size of Earth, but have the mass of the Sun

Once all the energy is gone, it becomes a black dwarf , which is a star that is dead and no longer emits light

Massive Stars - Supernova

Stephen Hawking - Supernova

Once massive stars reach the red giant phase, the core temperature continues to increase

The energy is eventually released in a powerful explosion called a supernova

Supernova – super giant explodes

The temperature of a supernova can reach 1,000,000,000 °C

Supernova

Famous Supernova Remnant - Crab Nebula

Neutron Stars A star that is 1.5 – 4 times as

massive as our sun becomes a neutron star after a supernova

Neutron stars spin rapidly giving off radio waves

Neutron star – core collapses and becomes very dense

If the radio waves are emitted in pulses, they are called pulsars

Black Holes

The most massive stars become black holes when they die

In a black hole, no nuclear fusion is taking place, so it is swallowed by its own gravity making it a black hole

Black holes are not visible

They must be detected by the x-rays which are given off

The Largest Black Holes in the Universe

Naked Science

Spaghettification

Lifetime of Stars

A star’s life cycle is determined by its mass!

The larger the mass, the shorter the life cycle

Small stars use up their fuel more slowly than large stars, so they have much longer lives

Small stars can live up to 200 billion years

Medium stars (like the sun) can live for about 10 billion years

Giant stars usually live for about 10 million years

Checkpoint

If a star is twice as massive as the sun, will it have a longer or shorter life than the sun?

Shorter!

Deaths of Stars

When a star begins to run out of fuel, the center of the star shrinks and the outer part of the star expands

The star becomes a red giant or supergiant

When a star runs out of fuel, it becomes a white dwarf, a neutron star, or a black hole

Life Cycle Animation - classzone

BBC - Describe StarsStars: Life and Death