1. Stars & Galaxies

2. A star is born…
A star is made up of a large amount of gas, in a relatively small volume.
A stellar nebula, on the other hand, is a
large amount of gas and dust,
spread out in an immense
volume.
All stars begin their lives as parts of stellar nebulas.

3. A star is born…
Gravity can pull some of the gas and dust in a nebula together.
The contracting cloud is
then called a protostar.
A star is born when the contracting gas and dust become so hot that nuclear fusion begins.

4. Lifetimes of Stars…
Before they can tell how old a star is, astronomers must determine its mass.
Medium - Mass stars, such as the Sun, exist for about 10 billion years.

5. Lifetimes of Stars…
Stars with more mass have shorter lives than those with less mass.
Small stars use up their fuel more slowly than large stars, so they have much longer lives, about 200 billion years.

6. Lifetimes of Stars…
Stars form in a stellar nebula, from collapsing clouds of interstellar gas and dust.
The rest of the life cycle depends on the mass of the star
When a star runs out of fuel, it will become a white dwarf, a neutron star, or a black hole.

7. Main Sequence Stars… Small and medium stars first become red giants.
Their outer layers expand to become red supergiants.
Eventually, the outer parts grow bigger still and drift out into space.

8. Main Sequence Stars... The blue, white, hot core is left
behind causing a white dwarf.
When there is no more energy, it becomes a black dwarf. It is the remaining burnt-out cinder left, as the star goes out.

9. Supernova…
A dying giant, or supergiant star, can suddenly explode. Within hours, the star blazes millions of times brighter.
The explosion is called a supernova.

10. Neutron Stars… After a star explodes, some material
from the star is left behind. This
material may become part of a
planetary nebula.
The core will compress
and form a neutron star.
Neutron stars are even
smaller and more dense
than white dwarfs.

11. Black Holes…
The most massive stars may have more than 40 times the mass of the Sun. One might have more than 5 times the mass of the Sun left, after it becomes a supernova.
The gravity of this mass is so strong that the gas is pulled inward, packing it into a smaller and smaller space. These massive stars become black holes when they die.