GALAXIES
Galaxies are collections of solar systems, gases, dust, and other astronomical objects, held together by gravity. These objects orbit around the center of the galaxy. Galaxies are classified by their appearance: for example, spiral galaxies, barred spiral galaxies, elliptical galaxies, peculiar galaxies and irregular galaxies. There are also galaxies known as ring galaxies. As their name implies, they hold the shape of rings. The galaxy shown in the background is our galaxy; the Milky Way. It is a barred spiral galaxy. Many astronomers believe there is a supermassive black hole at the center of the Milky Way, known as Sagittarius A. It is also believed that the Milky Way will at one point, collide with a spiral galaxy, the Andromeda galaxy, sometime in the distant future.
Stars are massive,illuminated balls of gas. Most of this gas is either hydrogen or helium. They are created in clouds of dust. Larger, more massive stars have shorter lifespans than smaller stars due to the fact that they burn off energy faster. Stars that are of average size become white dwarfs at the end of their lifespan. These white dwarfs will eventually cool down and fade away. Massive stars will explode in an eruption known as a supernova. Supernovae can produce neutron stars or black holes.
STARS