Some stars have a much different end of life than previously thought. Astronomers have observed for the first time traces of a star that exploded twice.
This discovery challenges current theories about supernovas. Researchers used the Very Large Telescope to study the remnants of the explosion, located 60,000 light-years away. The observed structures suggest an unexpected sequence of events.
An image of the double-detonation supernova SNR 0509-67.5 seen by the VLT.
Credit: ESO/P. Das et al. Background stars (Hubble): K. Noll et al.
White dwarfs, remnants of stars similar to the Sun, are at the heart of this study. Their explosion, known as a type Ia supernova, serves as a reference for measuring cosmic distances. This new observation could change our understanding of these phenomena.
The team identified patterns in the debris of supernova SNR 0509-67.5 that indicate a double explosion. This discovery suggests that some white dwarfs could explode without reaching the critical mass usually required, called the Chandrasekhar limit.
Scientists explain this phenomenon by the accumulation of helium around the white dwarf. The first explosion would be due to the instability of this layer, followed by a second explosion in the star's core.
This research, published in
Nature Astronomy, opens new avenues for understanding the diversity of stellar explosions.
What is a white dwarf?
A white dwarf is the compact remnant of a star with a mass similar to the Sun after it has exhausted its nuclear fuel. Unlike massive stars that end in supernovas, stars like the Sun end their lives by expelling their outer layers, leaving behind a dense, hot core.
These objects are extremely dense, with a mass comparable to the Sun's in a volume similar to Earth's. They slowly cool over billions of years, eventually becoming black dwarfs, although the Universe is not yet old enough for this to have happened.
White dwarfs play a key role in astronomy, particularly as precursors to certain supernovas. Their study helps us better understand stellar evolution and the dynamics of binary systems.
How are cosmic distances measured with supernovas?
Type Ia supernovas are often called 'standard candles' in astronomy. This name comes from their known intrinsic luminosity, which allows scientists to calculate their distance from Earth by measuring their apparent brightness.
The principle is similar to that of a flashlight whose light output is known. By observing its brightness, we can estimate its distance. Type Ia supernovas work the same way on a cosmic scale.
These explosions are so bright that they can be observed at considerable distances, providing a valuable tool for mapping the Universe. Their uniformity makes them reliable benchmarks for studying the expansion of the Universe and the nature of dark energy.