Black Holes
The intense gravitational field left when a giant star collapses
It is called a black hole because not even light can escape
Photon Sphere The outer edge where light bends but is still escapable
Event Horizon The point at which no light can escape
Singularity The shrunken star too small to be measured but with indefinite density
Galaxies
Galaxy A large assembly of stars and nebulae
Group of Galaxies
The Milky Way Our galaxy Flat disk with spiral arms
Three Types of Galaxies
Elliptical Oval shaped Most common type of galaxy found
Contains little gas and dust Most are dim and difficult to see
Spiral Dense center with spiral arms Bright and easy to see
Contains large amounts of gas and dust – always producing new stars
Irregular No specific shape Contains large amounts of gas and dust
Small and faint therefore hard to see
Quasars
Small, powerful source of energy thought to be cores of distant spiral galaxies
They emit radio waves and bright light
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