2A star is born…All stars begin their lives as NEBULAS, large clouds of gas and dust spread out in an immense volume.A STAR, on the other hand, is made up of a large amount of gas in a relatively small volume.
5(continued)In the densest part of the nebula, gravity pulls gas and dust together.A cloud of gas that has enough mass to form a star is called a PROTOSTAR.A star is finally born when the gas and dust from a nebula becomes so dense and hot that nuclear fusion starts.
7Lifetimes of stars… How long a star lives depends on its mass. Low mass stars (less mass than the sun): live for about 200 billion years.Medium mass stars (same as sun): live for about 10 billion years.High mass stars (15 times the mass of sun): live for about 10 million years.
8Death of stars…When a star begins to run out of fuel, its core SHRINKS and outer portion EXPANDS.Depending on its mass it can become either a RED GIANT or SUPERGIANT.
11(continued) Low/Medium mass -----> Red giant High mass > SupergiantAfter a star runs out of fuel, it becomes a white dwarf, neutron star, or black hole.
12White Dwarfs…After a small/medium mass star runs out of fuel, its outer layers expand, and becomes a RED GIANT.The outer parts keep growing until they form a glowing cloud of gas called a PLANETARY NEBULA.The blue-white core of the star that is left is called a WHITE DWARF.When a white dwarf stops glowing, it becomes a BLACK DWARF.
17Supernovas…After a high mass star runs out of fuel, its outer layers expand, and becomes a SUPERGIANT.When a supergiant runs out of fuel, it can suddenly explode, and within hours the star blazes millions of times brighter.The explosion is called a SUPERNOVA.
20Neutron Stars…After a supergiant explodes, some material is left behind.NEUTRON STARS are the remains of high mass stars.Smaller and denser than white dwrafs.Some neutron stars spin; these are called PULSARS.