A supernova revealed the most massive star known. Astronomers spotted the SN2007bi supernova in 2007 in a nearby dwarf galaxy and knew at once it was something different because it was up to a hundred times brighter than a typical supernova. After analyzing its signature, astronomers believe the star was about 200 times the mass of the Sun, making it the most massive star known. The previous record holder is Peony Nebula Star with about 175 solar masses.
The blast also confirmed that so-called pair-instability supernova exist, this type of supernova has long been a topic of debate as there were severe doubts that stars that massive could ever form.
In a pair-instability supernova, the star has neared the end of its life and exhausted its main supplies of hydrogen and helium, leaving it a core of mostly oxygen. In smaller stars, the core continues to burn until eventually it is all iron, then collapses in a Type II supernova, leaving behind a remnant black hole or neutron star.
But in the case of an extremely massive star, while its core is still made of oxygen, it releases photons that are so energetic, they create pairs of electrons and their anti-matter opposites, positrons. When the matter and antimatter meet, they annihilate each other. This reaction reduces the star's pressure, and it collapses, igniting the oxygen core in a runaway nuclear explosion that eats up the whole star, leaving no remnant at all.