In 1901, the star, GK Persei, located about 1500 light years from Earth became an astronomical sensation. Way up in the dark sky, it rapidly brightened, becoming the brightest star in the sky for several days, but it wasn’t a supernova, it was an explosion that is still having a significant impact on the surrounding space.
The explosion of GK Persei was triggered by the build-up of hot plasma on the surface of a white dwarf star. 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. For the first time scientists examined a detailed ‘time lapse’ x-ray image of the expansion of a classical nova explosion. Through this work, they hope to gain a better understanding of the expansion of gases in the universe, not only classical novae but also in supernovae – stellar explosions that are believed to be responsible for the creation of heavy elements such as uranium.
There is a great interest in understanding the dynamics of stellar explosions and especially supernovae, which are among the most powerful events that we know of in the universe. In these explosions, a collapsing star can outshine an entire galaxy. These events take place over enormous spans of time – the whole written history of mankind – so it is unfortunately impossible to observe the whole process as the remnant of the exploding star spreads out into the interstellar area around it. Scientists have to rely on comparing snapshots taken of different supernova at different stages of evolution.
Scientists found that although the nova remnant had expanded by approximately 90 billion kilometres during the 14 years, and 300 kilometres per second, the temperature of the plasma remained at a constant 1 million degrees Celsius. The light was fading but the dominant photons had not changed, implying that the nova remnant was moving into a region of lower density. Scientists say “For the first time we have a detailed image of how the nova propagates through space. Through this kind of study, we hope to be able to understand exactly how these powerful explosions expand into interstellar space, and it may ultimately give us new insights into the history of the cosmos.”