Life Cycle of a Star

Nebula(e) A Star Nursery! –Stars are born in nebulae. –Nebulae are huge clouds of dust and gas –Protostars (young stars) are formed when the dust and gas collapse (come together and become a dense “ball”) as gravitational attraction increases –Main sequence stars form when protostars further collapse

Nebula Dumbbell nebula

Large Ant Nebula

Horsehead nebula

How are different Stars formed? Nuclear fusion occurs in the center of the protostars Hydrogen fuses with other Hydrogen to form Helium Its size will change how fast the Hydrogen fuses, determining what type of star it will become

Fusion and Gravity The energy released by fusion causes the gases to expand while gravity tries to compact it. This battle continues throughout the life of the star. These two forces determine the stage and size of the star throughout its life.

Life of a Star Size of the star determines its life span. Example: Betelgeuse – red supergiant – 20 times more massive than the Sun; 14,000 times brighter –burns nuclear fuel 14,000 times faster than the Sun. –The Sun will live about 7,000 times longer than a massive star like Betelgeuse. Our Sun - 10 billion year life (5 Billion years have passed. –Stars less massive than the Sun have even longer life spans.

Main Sequence Stars - Young Stars Energy comes from nuclear fusion, nuclear fusionnuclear fusion – convert Hydrogen to Helium. –Most stars (about 90%) are Main Sequence Stars. Hotter = brighter (white, yellow, red). The hotter they are the quicker they burn The sun is a typical Main Sequence star.

Red Giant Relatively old star Relatively old star Diameter is about 100 times bigger than when first formed. Cooler than when formed (the surface temperature is under 6,500 K).

Red Giant After a few billion years the center of a star runs out of hydrogen. billionstarbillionstar It then begins to cool and contract. The outer layers of the star fall inwards and heat up the center. A shell surrounding the central core becomes hot enough to fuse protons so the star gains a new source of energy. Because it is hotter now, the outer parts start to swell. The star becomes a red giant.

Planetary 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.

Supernova

Supernova Supernovas occur when a red supergiant collapses. Supernovas are considered to be the most powerful explosions in the universe, as they represent the collapse of the most massive stars. Smaller supernovas leave the supergiant's core behind in the form of a neutron star.

Neutron Star Neutron stars are really dense. They have between 1.4 and 3 times as much mass as the Sun, but are compressed into a ball with a radius of about 10 km. A thimbleful of a neutron star would weigh more than 100 million tons on earth

Pulsars Neutron stars can sometimes be detected as pulsars Pulsars are neutron stars that rotate and emit electromagnetic radiation only along a single axis. They seem to “pulse”

Black Holes

Created when the remaining core of a giant star continues to collapse on itself, essentially creating a hole in space. Created when the remaining core of a giant star continues to collapse on itself, essentially creating a hole in space. Black holes are so dense that nothing entering its gravitational field ever escapes, not even light! The edge of a black hole, the point of no return, is referred to as the event horizon. Black holes are so dense that nothing entering its gravitational field ever escapes, not even light! The edge of a black hole, the point of no return, is referred to as the event horizon.