Life Cycle of a StarLife Cycle of a Star

Nebula(e)Nebula(e)

A Star Nursery!A Star Nursery!– Stars are born in nebulae. Stars are born in nebulae. – Nebulae are huge clouds of dust and gas Nebulae are huge clouds of dust and gas – ProtostarsProtostars (young stars) are formed when (young stars) are formed when

the dust and gas collapse (come together and the dust and gas collapse (come together and become a dense “ball”) as gravitational become a dense “ball”) as gravitational attraction increases attraction increases

– Main sequence stars form when protostars Main sequence stars form when protostars further collapsefurther collapse

NebulaNebula

Dumbbell nebula

Large Ant NebulaLarge Ant Nebula

Horsehead nebulaHorsehead nebula

How are different Stars formed?How are different Stars formed?

Nuclear fusion occurs in the center of the Nuclear fusion occurs in the center of the protostarsprotostars

Hydrogen fuses with other Hydrogen to form Hydrogen fuses with other Hydrogen to form HeliumHelium

Its size will change how fast the Hydrogen Its size will change how fast the Hydrogen fuses, determining what type of star it will fuses, determining what type of star it will becomebecome

Fusion and GravityFusion and Gravity

The energy released by fusion causes the The energy released by fusion causes the gases to expand while gravity tries to gases to expand while gravity tries to compact it.compact it.

This battle continues throughout the life of This battle continues throughout the life of the star.the star.

These two forces determine the stage and These two forces determine the stage and size of the star throughout its life.size of the star throughout its life.

Life of a StarLife of a StarSize of the star determines its life span.Size of the star determines its life span.

Example: Betelgeuse Example: Betelgeuse – red supergiant red supergiant – 20 times more massive than the Sun; 14,000 times 20 times more massive than the Sun; 14,000 times

brighterbrighter– burns nuclear fuel 14,000 times faster than the Sun. burns nuclear fuel 14,000 times faster than the Sun. – The Sun will live about The Sun will live about 7,000 times longer7,000 times longer than a than a

massive star like Betelgeuse. massive star like Betelgeuse.

Our Sun - 10 billion year life (5 Billion years have Our Sun - 10 billion year life (5 Billion years have passed. passed. – Stars less massive than the Sun have even longer life Stars less massive than the Sun have even longer life

spans. spans.

Main Sequence Stars - Young StarsMain Sequence Stars - Young Stars

Energy comes from Energy comes from nuclear fusion, , – convert Hydrogen to Helium. convert Hydrogen to Helium. – Most stars (about 90%) are Main Sequence Stars. Most stars (about 90%) are Main Sequence Stars.

Hotter = brighter (white, yellow, red). Hotter = brighter (white, yellow, red).

The hotter they are the quicker they burnThe hotter they are the quicker they burn

The sun is a typical Main Sequence star. The sun is a typical Main Sequence star.

Red GiantRed Giant

Relatively old star Relatively old star

Diameter is about 100 times bigger than Diameter is about 100 times bigger than when first formed.when first formed.

Cooler than when formed (the surface Cooler than when formed (the surface temperature is under 6,500 K). temperature is under 6,500 K).

Red GiantRed Giant

After a few After a few billion years the center of a years the center of a star runs runs out of hydrogen.out of hydrogen.

It then begins to cool and contract. The outer It then begins to cool and contract. The outer layers of the star fall inwards and heat up the layers of the star fall inwards and heat up the center. A center. A shell shell surrounding the central core surrounding the central core becomes hot enough to fuse protons so the star becomes hot enough to fuse protons so the star gains a new source of energy. Because it is gains a new source of energy. Because it is hotter now, the outer parts start to swell. hotter now, the outer parts start to swell.

The star becomes a The star becomes a red giantred giant. .

Planetary nebulaPlanetary nebula

When the helium core runs out, and the outer layers drift of away from the core as a gaseous shell, this gas that surrounds the core is called a Planetary Nebula.

The remaining core (that's 80% of the original star) is now in its final stages. The core becomes a White Dwarf the star eventually cools and dims. When it stops shining, the now dead star is called a Black Dwarf.

SupernovaSupernova

SupernovaSupernova

Supernovas occur when a red supergiant Supernovas occur when a red supergiant collapses.collapses.

Supernovas are considered to be the most Supernovas are considered to be the most powerful explosions in the universe, as powerful explosions in the universe, as they represent the collapse of the most they represent the collapse of the most massive stars. massive stars.

Smaller supernovas leave the supergiant's Smaller supernovas leave the supergiant's core behind in the form of a neutron star. core behind in the form of a neutron star.

Neutron StarNeutron Star

Neutron stars are Neutron stars are reallyreally dense. They have dense. They have between 1.4 and 3 times as much mass as between 1.4 and 3 times as much mass as the Sun, but are compressed into a ball the Sun, but are compressed into a ball with a radius of about 10 km. with a radius of about 10 km.

A thimbleful of a neutron star would weigh A thimbleful of a neutron star would weigh more than 100 million tons on earthmore than 100 million tons on earth

PulsarsPulsars

Neutron stars can Neutron stars can sometimes be sometimes be detected as pulsarsdetected as pulsars

Pulsars are neutron Pulsars are neutron stars that rotate and stars that rotate and emit electromagnetic emit electromagnetic radiation only along a radiation only along a single axis. They single axis. They seem to “pulse”seem to “pulse”

Black HolesBlack Holes

Black HolesBlack Holes

• Created when the remaining core of a Created when the remaining core of a giant star continues to collapse on itself, giant star continues to collapse on itself, essentially creating a hole in space. essentially creating a hole in space.

• Black holes are so dense that nothing Black holes are so dense that nothing entering its gravitational field ever entering its gravitational field ever escapes, not even light! The edge of a escapes, not even light! The edge of a black hole, the point of no return, is black hole, the point of no return, is referred to as the referred to as the event horizonevent horizon..