Stars can explode because of mysterious supersonic waves, a new study finds

During the star's explosion, it releases the same amount of energy it would release over its entire lifetime.


In a first, researchers have developed a theory describing how the nuclear reaction behind supernovae — bright and powerful explosion of stars — is triggered.

The study, published in the journal Science, noted that one of the processes triggering the stellar explosions was the formation of a mysterious supersonic reaction wave called detonation.

The researchers, including those from the University of Connecticut in the US, said these enigmatic waves travel faster than the speed of sound and are capable of burning up all of the star's material before dispersing into the vacuum of space.

Stars can explode because of mysterious supersonic waves, a new study finds

A false-colour composite of the Cassiopeia A supernova, with data from Spitzer, Hubble and Chandra telescopes. Image credit: NASA

As part of the study, the researchers demonstrated the process of detonation formation from a slow flame using both experiments and numerical simulations carried out on some of the largest supercomputers in the US.

They applied the results to predict the conditions of detonation formation in one of the classical theoretical scenarios of a type of stellar explosion called a 1a supernova.

This type of explosion, the study noted, happened when carbon and oxygen atoms are packed densely into around 1,000 tons per cubic centimetre in a star's core, and start burning to high temperatures in rapid nuclear reactions.

According to the researchers, the resulting explosion disrupts a star in a matter of seconds which ejects most of its mass while releasing a quantity of energy equal to what the star emits over its entire lifetime.

For the detonation process to occur, it must be confined within a wall like setting with obstacles, or boundaries, confining the pressure waves released from the burning, the study noted.

With increasing pressure, the researchers said, shock waves form and grow in strength to the point when they can compress the reacting mixture igniting it, and produce a self-sustaining supersonic boundary.

Light from a supernova explosion in the nearby starburst galaxy Messier 82 is reverberating off a huge dust cloud in interstellar space. The supernova, called SN 2014J, occurred at the upper right of Messier 82, and is marked by an “X.” The supernova was discovered on 21 January 2014. The inset images at the top reveal an expanding shell of light from the stellar explosion sweeping through interstellar space, called a “light echo.” The images were taken 10 months to nearly two years after the violent event (6 November 2014 to 12 October 2016). The light is bouncing off a giant dust cloud that extends 300 to 1600 light-years from the supernova and is being reflected toward Earth. SN 2014J is classified as a Type Ia supernova and is the closest such blast in at least four decades. A Type Ia supernova occurs in a binary star system consisting of a burned-out white dwarf and a companion star. The white dwarf explodes after the companion dumps too much material onto it. The image of Messier 82 reveals a bright blue disc, webs of shredded clouds, and fiery-looking plumes of glowing hydrogen blasting out of its central regions. Close encounters with its larger neighbor, the spiral galaxy Messier 81, is compressing gas in Messier 82 and stoking the birth of multiple star clusters. Some of these stars live for only a short time and die in cataclysmic supernova blasts, as shown by SN 2014J. Located about 11 million light-years away, Messier 82 appears high in the constellation Ursa Major, the Great Bear. It is also called the “Cigar Galaxy” because of the elliptical shape produced by the oblique tilt of its starry disk relative to our line of sight. The Messier 82 image was taken in 2006 using the Advanced Camera for Surveys. The inset images of the light echo also were taken by the Advanced Camera for Surveys. Links: NASA press release Video: zooming in on a light echo Video: zooming in on a light echo (annotated)

The supernova, called SN 2014J, occurred at the upper right of Messier 82, and is marked by an “X.” The inset images at the top reveal an expanding shell of light from the stellar explosion sweeping through interstellar space, called a “light echo.” The images were taken over 10 months to nearly two years after the violent event. Image credit: NASA

Stars do not have walls, making the formation of a detonation very enigmatic, the study noted.

The researchers developed a unified theory of turbulence-induced detonation which describes the mechanism and conditions for initiating the enigmatic process in thermonuclear explosions.

A reactive mixture, which burns and releases energy, when stirred up to create intense turbulence, builds up a catastrophic instability and may rapidly increase the pressure in the system.

This produces strong shocks that ignite a detonation, they said.

According to the researchers, thermonuclear combustion waves are similar to chemical combustion waves on Earth since they are both controlled by the same physical mechanisms.

This helped them use their findings to predict the conditions for detonation formation in Type 1a supernovae, they said.

The findings, according to the researchers, may also be applied to Earth-based combustion systems in which detonations can occur such as in industrial accidents involving gaseous explosions, as well as novel propulsion and energy conversion applications like detonation-based engines.

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