Back in 1901, a striking stellar object called GK Persei became the deserved focus of many astronomers’ attention. After bursting onto the celestial scene, this star held the title of the brightest in the sky for several days before slowly dimming. Now, more than a century later, scientists have learned that what they had been observing was actually a kind of “mini supernova” explosion, which occurred 1,500 years ago.
Before going boom, GK Persei was a smaller version of our sun, around eight times less massive, that was approaching the end of its drawn out stellar evolution. After exhausting all its nuclear fuel in the form of hydrogen, GK Persei became an extremely hot and dense object known as a white dwarf. These are so dense that a mere teaspoon of their matter would weigh a whopping 5.5 tons back on Earth.
But this wasn’t it for GK Persei; its gravitational pull was strong enough to begin dragging in material, mostly hydrogen, from its companion star. If enough gas is sucked in, nuclear fusion reactions can take place on the dwarf’s surface, eventually resulting in a dramatic boom that rips off its outer shell, ejecting the material into the surrounding space. These cosmic outbursts are known as “classical novas” and are considered small-scale supernovas, the dramatic explosions of massive stars. Unlike supernovas, however, these mini outbursts don’t result in the destruction of the entire star.
While classical novas may be much more commonplace than supernovas, they are still extremely important study targets to further our knowledge of stellar explosions. Furthermore, GK Persei is particularly interesting because it has revealed some intriguing insights into the environment surrounding the event.
After pointing the Chandra X-ray observatory at the nova on two separate occasions, spread out over a period of 13 years, scientists were able to glean important information about the changes in X-ray emissions that occurred over time. These data revealed that the explosion ejected material into space at staggering speeds of more than a million kilometers per hour (700,000 mph). That means that between observations, the debris spread out around 145 billion kilometers (90 billion miles).
But what is perhaps most interesting is that while this stellar corpse decreased in X-ray luminosity by around 40% over the 13 years, its temperature barely changed. This find was unexpected given the fact that the shock wave produced by the explosion should have left a trail of cooler temperatures as it expanded and heated more and more matter. According to a NASA statement, this “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 could indicate, NASA says, that the wave is traveling through a less dense area than before.