These stars make up the vast majority of objects in the night sky, encompassing roughly 90% of all the stars in the universe. Main sequence stars represent protostars that successfully begin nuclear fusion in their core. Types of StarsĪstronomers place the stars in our universe into one of four categories: main sequence stars, giants, supergiants, and dead stars. The brightest stars have the number 0, whereas the dimmest is number 9. This system uses letters to designate stars in decreasing temperature.Įach star’s spectral type is supplemented by a number that depicts its absolute brightness. The most common way we classify stars is through the Morgan–Keenan (MK) system, which groups these celestial objects based on color and temperature. This can lead to the complete destruction of a protostar, or a star can save itself by blowing off only its outermost layers. If a condensing cloud is too big, nuclear reactions occur so quickly that these forming stars explode from the inside out. They are incredibly rare in our universe and only make up about 1% of all star-like objects. Such objects are called brown dwarfs.īrown dwarfs never reach the size of an average star and are very dim.

While the surface of the forming protostar shows some heat, it will never become a star. If a cloud is too small in size, it will contract and heat up but will never reach a temperature to begin nuclear fission. Not All Clouds Become StarsĪs interstellar clouds collapse, they don’t always meet the criteria to successfully form stars.

Once a protostar reaches a core temperature of 10,000,000 Kelvin (K), nuclear fusion begins, and a star is officially born. These cores, also known as protostars, continue to heat and shrink. As sections of this cloud reach a critical density, they collapse into dense cores.

In the seemingly infinite universe, gas and dust particles find each other and form clouds.

Name a blue main sequence star