Life cycle of stars

Life cycle of stars

• During the collapse, the material heats up by frictional processes and begins to radiate infra-red radiation so astronomers are hoping to detect this to confirm the formation process. This is very difficult because the protostar would have a lot of gas and dust still surrounding it (a Bok Globule).• Stars are formed in groups as the different parts of the original nebula collapse.

Travelling at the speed of light (or radio wave)300,000 km /sec

8 minutes

6 hours

4 years

sun

nearest star

pluto

100,000 light years

100 billion stars

Milky way galaxyAndromeda galaxy

Our sun is one of millions of stars in a group of stars called a galaxy

100,000 light years

100 billion stars

Light from our nearest galaxy has taken 2 million years to reach us!

Milky way galaxyAndromeda galaxy

Our sun is one of millions of stars in a group of stars called a galaxy

BIRTH OF A STAR

* A star forms from a huge cloud of dust and gas.

* Gravity slowly pulls the material together.

* Rocks crash into each other and heat up.

Our sun 4,500 million years ago.

• During the collapse, the material heats up by frictional processes and begins to radiate infra-red radiation so astronomers are hoping to detect this to confirm the formation process.

BIRTH OF A STAR

* A star forms from a huge cloud of dust and gas.

* Gravity slowly pulls the material together.

* Rocks crash into each other and heat up.

Our sun 4,500 million years ago.

* Nuclear reactions begin and the star starts to shine.

Our sun 4,500 million years ago.

BIRTH OF A STAR

Planets are natural satellites

of the sun * Smaller masses cool to form planets which orbit the sun under gravity.

* During a star’s life time, nuclei of lighter elements (mainly hydrogen and helium ) fuse to produce nuclei of heavier elements

* Nuclear reactions begin and the star starts to shine.

THE HERTZSPRUNG - RUSSELL DIAGRAM

LIGHT

INTENSITY

Wave length of light emittedBlue Red

HOT Cold

Newly formed stars join the ‘main sequence’at a point on the graph that relates to its mass.

THE STABLE LIFE OF A STAR

THE STABLE LIFE OF A STAR

THE STABLE LIFE OF A STAR

- Our sun stays on main sequence for 10 billion years

- If star mass is 15 x suns mass

then 10 million years.

Stars of greater mass than our sun (have higher core temperatures)can fuse heavier elements up to iron releasing even more energy.

Dark matter (ash)

Super nova

Explosionfusing heaviestknown elementseg 92U

Explosionfusing heaviestknown elementseg 92UalsoNew young starsand condensing

planets may form

Neutron star:p + e n v. dense !

Neutron star:p + e n v. dense !

For very massive stars, the material is so dense,the force of gravity so strong , that light itself cannot escape.

Nebular

Protostar Main Sequence

star

Red giantWhite dwarf

P3 4.2 The life history of a star similar in size to our sun

Protostar Gravity draws atoms together, releasing energy star heats up but does not shine,

Gravity draws atoms together, releasing energy Nebular

The star shines during fusion of hydrogen to helium for billions of years; outward radiation pressure is balanced by inward pull of gravity.

Star

Red giant Most of Hydrogen has been used, now helium fuses to make carbon, unused hydrogen is ejected to the surface, cools and appears red.

White dwarf Fusion stops, gravitational collapse occurs, star heats up and changescolour from red to yellow to white. It finally becomes cold dark matter.

Nebular

Protostar Main Sequence

star

Red giantWhite dwarf

P3 4.2 The life history of a star similar in size to our sun

Protostar Gravity draws atoms together, releasing energy star heats up but does not shine,

Gravity draws atoms together, releasing energy Nebular

The star shines during fusion of hydrogen to helium for billions of years; outward radiation pressure is balanced by inward pull of gravity.

Star

Red giant Most of Hydrogen has been used, now helium fuses to make carbon, unused hydrogen is ejected to the surface, cools and appears red.

White dwarf Fusion stops, gravitational collapse occurs, star heats up and changescolour from red to yellow to white. It finally becomes cold dark matter.

Nebular

Protostar Main Sequence

star

Red giantWhite dwarf

P3 4.2 The life history of a star similar in size to our sun

Protostar Gravity draws atoms together, releasing energy star heats up but does not shine,

Gravity draws atoms together, releasing energy Nebular

The star shines during fusion of hydrogen to helium for billions of years; outward radiation pressure is balanced by inward pull of gravity.

Star

Red giant Most of Hydrogen has been used, now helium fuses to make carbon, unused hydrogen is ejected to the surface, cools and appears red.

White dwarf Fusion stops, gravitational collapse occurs, star heats up and changescolour from red to yellow to white. It finally becomes cold dark matter.

Nebular

Protostar Main Sequence

star

Red giantWhite dwarf

P3 4.2 The life history of a star similar in size to our sun

Protostar Gravity draws atoms together, releasing energy star heats up but does not shine,

Gravity draws atoms together, releasing energy Nebular

The star shines during fusion of hydrogen to helium for billions of years; outward radiation pressure is balanced by inward pull of gravity.

Star

Red giant Most of Hydrogen has been used, now helium fuses to make carbon, unused hydrogen is ejected to the surface, cools and appears red.

White dwarf Fusion stops, gravitational collapse occurs, star heats up and changescolour from red to yellow to white. It finally becomes cold dark matter.

Nebular

Protostar massivestar Super red

giantSuper nova

P3 4.2 The life history of a star several times larger than our sun

The explosion compresses the core into very densely packed neutrons. If the original star was more massive a black hole would be created. (The gravitational field is so strong that not even light can escape from it.)

Fusion stops, gravitational collapse occurs, star heats up and changes colour from red to yellow to white. After further collapse it explodes as a supernova! (Outshines a galaxy for several weeks)

Neutron Star:

Super Nova:

White dwarf

Nebular

Protostar massivestar Super red

giantSuper nova

P3 4.2 The life history of a star several times larger than our sun

The explosion compresses the core into very densely packed neutrons. If the original star was more massive a black hole would be created. (The gravitational field is so strong that not even light can escape from it.)

Neutron Star:

Fusion stops, gravitational collapse occurs, star heats up and changes colour from red to yellow to white. After further collapse it explodes as a supernova! (Outshines a galaxy for several weeks)

Super Nova:

White dwarf