New VLT image reveals first visual evidence of rare Type Ia supernova explosion mechanism – which erupted twice
Astronomers have for the first time obtained visual evidence that a star exploded not once – but twice. Using the European Southern Observatory's Very Large Telescope (ESO's VLT) in Chile, they examined the remnants of ancient supernova SNR 0509-67.5 and found patterns in it that suggest a rare mechanism: a double explosion. The discovery was published in the journal Nature Astronomy, and it sheds new light on one of the most energetic celestial phenomena in the universe.
Most supernovae are the dramatic end of massive stars, but there is another type – type Ia – that begins with a small, inactive star: a white dwarf. White dwarfs are the compact remnants of sun-like stars that have exhausted their nuclear fuel. When a white dwarf is in a pair of stars, it may accumulate material from its companion until a massive explosion occurs.
“White dwarf explosions play a crucial role in astronomy,” explains Priyam Das, a doctoral student at the University of New South Wales in Canberra, Australia, who led the study. “They are essential for measuring the expansion of the universe, and they are also the main source of iron on Earth – including the iron in our blood.” However, he notes, “the exact mechanism that triggers this explosion has remained a long-standing mystery.”
The conventional model of a Type Ia supernova describes a situation where the white dwarf absorbs material until it reaches a critical mass (known as the Chandrasekhar limit), after which a single explosion occurs. However, in recent years, alternative scenarios have been proposed, including Double explosion Which occurs before the star reaches this mass. In this scenario, a layer of stolen helium builds up around the white dwarf, which explodes first, creating a shock wave that leads to a second explosion in the star's core – and thus the supernova is created.
Until now, there has been no direct evidence that such a mechanism actually occurs in nature. But now, a new observation provides the strongest visual evidence yet for the existence of a double explosion. Using the MUSE spectrometer on ESO’s Very Large Telescope, astronomers have been able to identify a unique structure in the supernova remnant – two separate shells of calcium. This pattern was predicted by the double explosion model, and is a clear “fingerprint” for this scenario.
Dr. Ivo Seitzenzel, who led the observations while working at the Institute for Theoretical Research in Heidelberg, Germany, says the results show that "white dwarfs can explode even before they reach the known critical mass – and the double explosion mechanism does indeed occur in nature."
Type Ia supernovae are essential to understanding the universe: their uniform behavior allows them to be used as a "cosmic tape measure" to measure galactic distances. For example, they were used to discover the accelerating expansion of the universe - a discovery that won the Nobel Prize in Physics for their discovery in 2011. Understanding their explosion mechanism is essential to explain why they are so consistent in brightness.
Das adds that “this visual not only helps to solve an ancient mystery, but also provides a spectacular sight to the eye – a beautiful layered structure created by the cosmic explosion.” He says, “To reveal the inner workings of such an explosion is simply deeply satisfying.”
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