Extreme explosion

The electromagnetic spectrum is vast, ranging from high-energy gamma rays all the way to low-energy radio waves. Different telescopes and instruments are optimised to detect different regions of this spectrum — for example, ESA’s XMM-Newton and Integral space observatories study the high-energy Universe, scouring the skies for X-rays and gamma rays.

One cosmic source of such high-energy radiation is the phenomenon shown in this ESA artist’s impression as an ethereal blue glow: a gamma-ray burst.

These bursts are extraordinarily high-energy events, created when a star in a distant galaxy explodes at the end of its life. This produces an intense stream of gamma rays that can last from a few seconds to a few hours. This violent burst then fades away, leaving a fainter afterglow that can be seen at X-ray, optical and radio wavelengths.

ESA’s Integral observatory is capable of observing these intense initial bursts. However, the gamma-ray explosion itself is often very short-lived, making it extremely difficult to pinpoint and observe a burst as it happens. Luckily, Integral and XMM-Newton can also search for and observe the dimmer X-ray afterglow that follows, using it to trace both the composition and the location of a gamma-ray burst.

Gamma-ray bursts emit such an enormous amount of energy that, when at their peak, they are the brightest and most powerful phenomena in the Universe. The source of such an extraordinary amount of energy is still uncertain, but there are several theories: jets escaping from the turbulent environment around a forming black hole, the merging of two compact objects such as neutron stars, or a beam of energy from a hypernova – a very energetic type of supernova explosion following the death of an extremely massive star.

An average gamma-ray burst might last on the order of milliseconds to minutes, but astronomers recently discovered another class of ultra-long burst. These continue to spew out gamma-rays for several hours before settling down to an afterglow. Only a handful of these events have been identified, but they are likely caused by the demise of a specific type of star known as a blue supergiant.

Although relatively rare in the nearby Universe, these very massive stars are thought to have been commonplace in the early Universe, with most of the very first population of stars having evolved into them over the course of their lives. Understanding more about their extreme nature may give clues about the primordial Universe. Read more here.