Out There

Most black holes are the result of a massive star explosion. As the star explodes, its core is crushed by gravity until it disappears from sight. Gravity becomes so extreme that it overwhelms all other forces in the universe. Not even light can escape.

Image at right: A growing black hole, called a quasar (courtesy of NASA/JPL-Caltech).

Our Solar System is in the Milky Way galaxy, one of hundreds of billions of galaxies in the observable Universe.

Image at right: A picturesque spiral galaxy known as Messier 81, or M81 (courtesy of NASA/JPL-Caltech/ESA/Harvard-Smithsonian CfA)

Twinkle, twinkle, little star. How I wonder what you are. Well, wonder no more! Stars are large balls of extremely hot gas or, more accurately, hot gas and a gas-like substance called plasma. They are primarily composed of the two most common elements in the universe: hydrogen and helium.

Image at right: White dwarf stars (courtesy of NASA and H. Richer, University of British Columbia).

Gas, dust and debris from star explosions and around star-forming regions are called nebulae (plural of nebula). Nebulae are often very large and span across many light-years.

Image at right: The Horsehead Nebula, Nigel Sharp (NOAO), KPNO, AURA, NSF (courtesy of NASA).

Extrasolar planets, or exoplanets, are planets outside of our Solar System, so they do not orbit our Sun. Exoplanets that orbit other stars are difficult to detect directly because they are literally lost in the glare of their stars.

Image at right: Artist concept of an extrasolar planet (Courtesy of NASA).