A big ball of hot gases in space is called a star.
It is called a neutron star.
A star
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Well for shore the biggest star in our solar system is called "Betelgeuse" not many people know how hot Betelgeuse is!
Yes, a star's outer layer, called the photosphere, is hot and dense. This is where most of the visible light and heat emitted by the star originate. The temperature and density of the photosphere vary depending on the type and age of the star.
Many newly detected extrasolar planets are called hot Jupiters because they are large, gaseous planets with characteristics similar to Jupiter, but they orbit very close to their host star. This proximity to their star causes them to have high surface temperatures, hence the term "hot."
A star, or a sun. (If it's close, it's a sun. If it's a long way away, it's a star.)
A protostar. See related question.
Yes, a star is a glowing sphere of hot gas.
The blue star is the hottest star.
The outermost atmosphere of a star is called Stellar atmosphere. Within the Stellar atmosphere, the corona is the outermost part. The corona mostly consist of plasma which has a temperature above a million Kelvin.