Life Cycles of Stars Where we’re going today… Learning about where Stars come from and where they go By the end of this class, you should be able to… Name the process and fuel used by stars. Describe the life cycle of a low mass star. Describe the life cycle of a intermediate mass star. Describe the life cycle of a high mass star. What is a black hole?

Life Cycles of Stars Stars A star is an object in space made up of hot gases, with a core that is like a thermonuclear reactor. The astronomer Carl Sagan once said… “there are more stars in the universe than grains of sand on all the beaches of Earth.” In between stars there is interstellar matter, which is made up of gas (mostly Hydrogen) and dust. Birth of a Star Gravity attracts chunks of gas and dust in a nebula to come together

Life Cycles of Stars Over time, gravity causes the mass to grow and eventually the material collapses in on itself and contracts forming a “protostar” If the mass stays the same, the protostar may shrink and never reach full star status.

Life Cycles of Stars If it collects enough mass (dust and gas), then the protostars core reaches 10 000 000°C and its atoms in the core start to fuse together to form larger single atoms. Nuclear Fusion – Hydrogen (H) atoms combine to form Helium (He) At this point the star starts to glow and leftover gas and dust disperse Energy radiates from the core in every direction as electromagnetic waves This is how our SUN keeps the Earth warm.

Life Cycles of Stars Evolution of a Star The life cycle of all stars start in nebula’s, but differ depending on the mass of the newborn star… Low Mass Stars Small, dim and cool red dwarfs (stays like this for most of their life) These burn their H fuel very slowly and may last for as long as 100 billion years

Life Cycles of Stars Eventually a red dwarf changes into a very hot, but small, dim white dwarf and quietly burns out

Life Cycles of Stars Intermediate Mass Stars Similar to our sun (stays like this for most of their life) These burn H fuel faster than low mass stars and last only about 10 billion years Eventually, an intermediate mass star expands into a red giant and sheds much of its material into space It then collapses in on itself and slowly shrinks into a small, dim white dwarf As it cools more, it turns into a black dwarf, a dense, dark body made up mostly of carbon and oxygen

Life Cycles of Stars

Life Cycles of Stars High Mass Stars 12 or more times the mass of the Sun These stars consume their fuel faster and become red giants (they last for only 7 billion years) When their fuel is used up, these massive stars become supergiants Before long, they collapse in on themselves causing a massive explosion called a supernova This is important as it spreads heavy elements out through space.

Life Cycles of Stars If the star began with a mass about 12 to 15 times that of the Sun, the remaining core eventually collapses and forms a neutron star. Neutron stars can start out as large as 1 million km wide but collapse into a sphere only 10 km wide. The core of a neutron star is 100 000 000°C and may take trillions of years to cool.

If a star is more than 25 times as massive as the Sun, the star collapses into itself and becomes a black hole…

Life Cycles of Stars Black holes Black holes are extremely dense and so they have an extraordinary amount of gravitational pull. This pull is so strong that not even light can escape their powerful gravitational force How do astronomers know that black holes exist? • Material pulled toward the black hole emits electromagnetic radiation that can be measured • The intense gravity of black holes has observable effects on passing stars and galaxies

Life Cycles of Stars • Results from computer models show how super-dense objects distort light from distant stars (and these match observations of suspected black holes)

Life Cycles of Stars Did we get there… Can you… Name the process and fuel used by stars. Describe the life cycle of a low mass star. Describe the life cycle of a intermediate mass star. Describe the life cycle of a high mass star. What is a black hole? Assignment: Origin of a Star (Concept Map)