Star Life Cycle Stellar Evolution Life of the

Star Life Cycle

Stellar Evolution: Life of the n The most massive stars have Star the shortest lives. Stars that are 25 to 50 times that of the sun live for only a few million years. Stars like our Sun live for about 10 billion years. Stars less massive than the Sun have even longer life spans n Stars are like humans they are born, live and die

The Birth of Stars are formed in 1. Nebulae, interstellar clouds of dust and gas (mostly hydrogen). These stellar nurseries are abundant in the arms of spiral galaxies. In these stellar nurseries, dense parts of these clouds undergo gravitational collapse and compress to form a rotating gas globule. It begins to spin as it shrinks

NEBULA PICTURES

Protostar stage: The nebula flattens and the center condenses: Temps start to increase due to friction (more collision of molecules). When temps reach 10 million K, NUCLEAR FUSION begins Nuclear Fusion generates the energy for a star. When fusion begins, it is officially considered a STAR. (yeah!) Fusion – combining a lightweight nuclei into a heavier nuclei

Protostar Pictures

Main-Sequence Stage The protostar is now a stable main sequence star which will remain in this state for about 10 billion years. After that, the hydrogen fuel is depleted and the star begins to die. Stars live out the majority of their lives in a phase termed as the Main Sequence. Longest stage of a star

Main Sequence Star

RED GIANT STAGE When a star has burned between 10% and 20% of its hydrogen, its core will to run out of fuel. At this stage, the star is entering the end of its life. The diameter of the star can increase by a factor of 200, while its cooling is translated into a reddening of its radiation : the star is becoming what is called a red giant.

n n n Star has run out of Hydrogen atoms in the core to undergo fusion. Our sun has used only about 5% of its Hydrogen Star expands about 10 x bigger and cools. Its luminosity increases, temp decreases. ***** Helium fuses to form Carbon, and the core shrinks. It begins losing outer layers

BETELGEUSE –RED GIANT F. Y. I. n Only a few million years old, Betelgeuse is already dying. Astronomers predict that it's doomed to explode as a soon, within 1, 000 years or so, an event that will be spectacular for Earth's future inhabitants. (Conceivably, it's already happened as Betelgeuse is 640 light-years away!)

• Star size comparison

Burnout and Death n n n Fate of a Star depends on its mass All stars, regardless of size, run out of fuel and collapse due to gravity A star will become either a black dwarf, neutron star, or black hole, depending on how massive it was. .

Death of low-mass stars Never evolve into red giants n Remain stable main-sequence stars until hydrogen is gone n Collapse into white dwarfs n

**Death of medium-mass stars** Sun-like Stars (Mass under 1. 5 times the mass of the Sun) Red Giant --> Planetary Nebula -->White Dwarf --> Black Dwarf n

**Death of massive stars** Huge Stars (Mass between 1. 5 to 3 times the mass of the Sun) Red Super. Giant --> Supernova --> Neutron Star n Giant Stars (Mass over 3 times the mass of the Sun) Red Super. Giant --> Supernova --> Black Hole n

PLANETARY NEBULA This is left when a giant loses its outer layers of gas. n Leaves only the core. n The core will become a white dwarf n

Planetary nebula pictures

WHITE DWARF Only hot, dense core is left of this star. n It will shine for billions of years before cooling. n Stable star with no nuclear fuel, radiates left over fuel for billions of years n Could become a black dwarf, but the universe is not old enough to form these

White Dwarf Pictures

SUPER NOVA n Super Giant eventually loses its outer layers in an explosion leaving only the core – this is the super nova.

Eventually this core collapses (in an instant). As the iron atoms are crushed together in this gravitational collapse, the core temperature rises to about 100 billion degrees. The repulsive electrical forces between the atoms' nuclei overcomes the gravitational forces, causing a massive, bright, short-lived explosion called a supernova. During the explosion, shock waves, blow away the star's outer layers.

NEUTRON STAR After a Super Nova explosion, the core may condense into a small core of neutrons. n It is so dense – 1 spoonful of Earth would weigh 100 million tons. n Rotates very rapidly. If the star's remaining mass is between 1 1/2 to 3 times the mass of the Sun, it will collapse into a small, dense neutron star (about ten miles in diameter, about 1. 4 times the mass of the Sun, with an extraordinarily strong magnetic field, and rapid spin). n

Neutron Star Pictures

BLACK HOLE This is the 3 rd predicted result to a star. n This is the most dense core of a star that can be left. n Gravity is so strong, light cannot escape. n Makes it look like a dark hole in space. If the star's remaining mass is greater than three times the mass of the Sun, the star contracts tremendously and becomes a black hole n

Black Hole Pictures Anatomy of a black hole

The density of a star is pre-determined based on its weight (the amount of dust and gas) it begins with. n Smaller stars become white dwarfs. n Very large stars become neutron stars or black holes. • Life Cycle of a Star Video n