Black hole

According to the general theory of relativity, a black hole is a region of space from which nothing, including light, can escape. It is the result of the deformation of spacetime caused by a very compact mass. Around a black hole there is an undetectable surface which marks the point of no return, called an event horizon. It is called “black” because it absorbs all the light that hits it, reflecting nothing, just like a perfect black body in thermodynamics. Under the theory of quantum mechanics black holes possess a temperature and emit Hawking radiation.

An asteroid is like a planet, but smaller. The name “asteroid” means “like a star” in the ancient Greek language. Asteroids may look like small stars in the sky, but they really do move around the Sun, while stars only seem to move because the Earth spins. Like planets, asteroids do not make their own light. Because of this, some people think “asteroids” is not a good name, and think that the name “planetoid” (”like a planet”) would be a better name.

Most asteroids are made of rock, but some are made of ice or metal. Most asteroids in our Solar System are in the asteroid belt between Mars and Jupiter.

A nebula is usually made up of hydrogen gas and plasma. It is the first stage of a star’s cycle. There are four different types of nebula. These are; Emission, Reflection, Dark, and Planetary. Opinions on the number of Nebulae do vary, however, and some of these other types include Planetary and Bright nebula. In the past Galaxies and Star Clusters were also thought to be certain types of nebulae.