There are billions of trillions of stars spattered across a vast universe, most of which we will never be able to see. Of the ones we can, many are long dead, their light only now reaching us after traveling for eons through space. These ancient twinkles allow us to glimpse the universe as it looked billions of years ago, helping us read the timeline of its evolution.
Neutron stars, for example, are some of the smallest and densest stars in the universe. They form when massive stars explode in supernovae, each leaving behind a core that collapses in on itself and squeezes electrons and protons together into neutrons. Sometimes neutron stars are so dense they collapse into black holes. And one hypothesis suggests that if they are not dense enough, they may turn into “strange stars,” made of even smaller subatomic particles called quarks.