‘Mini supernova’ gives insights to larger cosmic blasts

Astronomers at NASA’s Chandra X-ray Observatory believe a small nova explosion – a sort of “mini supernova” – may provide clues to the dynamics of other, much larger stellar eruptions. 

A nova can occur if the strong gravity of a white dwarf pulls material from its orbiting companion star – mostly hydrogen gas – that accumulates on the surface of the white dwarf, resulting in intense nuclear fusion reactions that culminate in a cosmic-sized hydrogen bomb blast.

The outer layers of the white dwarf are  blown away, producing a nova outburst that can be observed for a period of months to years as the material expands into space.

The latest study is of the nova GK Persei, which suddenly appeared in 1901 as one of the brightest stars in the sky for a few days, before gradually fading away in brightness.

Chandra first observed GK Persei in February 2000 and then again in November 2013 giving astronomers time to measure important differences in the X-ray emission and its properties.

Over the years, the nova debris expanded at a speed of about 1.13 million kph, with the blast wave moving about 145 billion kilometres during that period.

One intriguing discovery was that while the X-ray energy emitted by the GK Persei remnant decreased by about 40% over the 13 years, the temperature of the gas in the remnant remained constant, at about one million degrees Celsius.

As the shock wave expanded and heated an increasing amount of matter, the temperature behind the wave of energy should have decreased. The observed fading and constant temperature suggests that the wave of energy has swept up a negligible amount of gas in the environment around the star over the past 13 years. This suggests that the wave must currently be expanding into a region of much lower density than before, giving clues to stellar neighborhood in which GK Persei resides.

A paper describing these results appeared in the 10 March issue of The Astrophysical Journal. The authors were Dai Takei (RIKEN, Spring-8 Center Japan), Jeremy Drake (Smithsonian Astrophysical Observatory), Hiroya Yamaguichi (Goddard Space Flight Center), Patrick Slane (Smithsonian Astrophysical Observatory), Yasunobu Uchimaya (Rikkyo University, Japan), Satoru Katsuda (Japanese Aerospace Exploration Agency).

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