White dwarf stars often exploded at lower masses in the distant past

Scientists studying white dwarf stars have made an interesting discovery in recent research. The team was studying small and dense white dwarf stars when they explode. Some of them create bright, and short-lived flares called Type Ia supernovae.

The scientists say that type of supernovae is informative cosmological markers for astronomers. They help scientists prove that the universe is accelerating in its expansion. The team says that not all white dwarfs are the same; they often range from about half the mass of the sun to almost 50% more massive than the sun.

White dwarfs can explode into Type Ia supernovae, and some of them die quietly with no explosive fanfare. Caltech scientists studying these white dwarfs have found that early in the history of the universe, white dwarfs often exploded at lower masses than they do today. The discovery indicates that the white dwarf stars might explode from a variety of causes and may not need to hit a critical mass before they explode.

When a star similar to our sun nears the end of its life, they shrink into dim, dense white dwarf stars with all their mass placed into an object about the size of the Earth. Sometimes they explode and sometimes not, science is uncertain why that happens. A scientist called Subrahmanyan Chandrasekhar calculated in the early 1900s that if a white dwarf had more than 1.4 times the mass of the sun, it would explode in a Type Ia supernova.

However, the scientist's calculation didn't explain why white dwarfs with less than 1.4 solar masses also sometimes explode. The team has been using the Keck II telescope to try and answer that question. The discovery was that most of the stars in ancient galaxies ran out of material to form stars in the first billion years of the life of the universe. Most of the stars in those universes are low in nickel, but they still exploded. The team is conducting research to try and figure the mystery out. The next step for the team is to study elements other than nickel, particularly manganese.