The Hubble Space Telescope took this picture of a group of stars in the constellation of Sagittarius. Blue stars can be seen scattered across the frame, set against a backdrop of red companions. This blue stars are young, most likely formed at the same time from the same collapsing molecular cloud.

Red stars are much cooler than the sun, so they are either at the end of their lives or they are much less massive. These lower-mass stars are called red dwarfs and are thought to be the most common type of star in the Milky Way. The blue stars are hot. They are either young or very massive, many times the mass of the Sun.

A star’s mass decides its lifespan. Massive stars burn brightly over a short lifespan and die after only tens of millions of years. Yellow stars like the Sun typically live longer, burning for approximately ten billion years. Smaller stars, on the other hand, live life in the slow lane and may exist for trillions of years.

Image Credit: NASA