1. Most of the stars you view from the earth at night are actually binary stars. That is, two stars circle each other creating an imagined point of gravitation, or a smaller star circles around the “main star”. Sometimes these main stars draw material from the smaller one, as they come closer to each other. There is a mass limit that a planet can hold without fusing nuclear reaction. If Jupiter was larger it might have fused as a brown dwarf, a kind of semi-star, many moons ago. It is actually more common in other solar systems, evidenced by their relative lack of planets. This is because most of the material which is locked in the gravitational field of the main star gathers up in one place, which in the end lights up as a star and forms a binary system. There can also be more than two stars in one system, yet binary systems are more common.
2. White dwarfs are so called “dead stars”. After the red giant phase, our own star – the Sun – will end up as a white dwarf. White dwarfs have the radius of a planet (like earth, not like Jupiter), yet the density of a star. These densities are made possible by electrons separating from the atomic nuclei they circle, increasing the amount of space which these atoms inhabit and creating a great mass and small radius dynamic. If you could hold an atom's nuclei in your hand, the electron would circle around it at a distance of 100 meters or more. In the case of electron degenerated matter, this space is free to use. In the end, white dwarfs will cool down and cease emitting light. These massive bodies cannot be seen and no one knows how many of them lie quietly throughout the universe.
3. If a star is big enough to avoid the final white dwarf phase, but small enough to avoid becoming a black hole – it will end up as an exotic type of star, know as a neutron star. The case of neutron stars is somewhat similar to white dwarfs, in that they are also degenerated matter - but differently degenerated.
X-ray neutron star
Neutron stars are formed from so called neutron degenerated matter – that is when all electrons and positively charged protons escape and only neutrons are left to form the bulk of the star. The density of neutron star is comparable to the density of an atom nuclei. Neutron stars can have mass similar to our sun or slightly higher but their radius is less than 50 kilometers: usually 10-20km. A teaspoon of this neutron degenerated matter weights 900 times the mass of the Great Pyramid of Giza.
Neutron star scale
If you observe a neutron star directly, you would be able to see both poles of it, because the neutron star works as gravitational lens, curving light around itself through its massive gravitational pull. A special case of a neutron star is the pulsar. Pulsars can revolve themselves at around 700 revolutions per second, emitting radiation which appears to blink – hence the name.
Scale of Eta Carinae
4. Eta Carinae is one of the biggest stars there is. It is about 100 times “heavier” than our sun and has a radius of about the same scale or more. It can shine at a million times brighter than our sun, which is quite impossible for us to comprehend. Usually these hyper-massive stars are quite short lived because they literally burn themselves out. Scientists believe that 120 times the mass of the Sun is the limit that no star can go above.
5. Pistol Star – a hyper-giant similar to Eta Carinae that has had problems keeping itself cool. It is so hot that its own gravitation has struggles to hold itself together; as a result the Pistol Star emits what is known as “solar wind” (high energy particles which, for example, create the Northern Lights) and is 10 billion times stronger than our sun. Because of the massive levels of radiation, it is impossible to imagine life ever existing on this star system, no matter how far advanced technology becomes.