Space

Energetic superflare with the power of 80 billion megatonnes of TNT erupts from tiny star

Energetic superflare with the ...
Artist's impression of a superflare on an L dwarf star
Artist's impression of a superflare on an L dwarf star
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Artist's impression of a superflare on an L dwarf star
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Artist's impression of a superflare on an L dwarf star

Astronomers have discovered a rare superflare more powerful than anything observed on our Sun in modern times, erupting from a small, cold star roughly the size of the planet Jupiter. While the effects of such a superflare would be devastating to our technology dependent society, it could help kickstart the evolution of life on distant alien worlds.

Solar flares are thought to occur when magnetic energy that has built up in a star's interior is suddenly and dramatically released. This causes charged particles to heat up plasma on the surface of the star, culminating in the explosive release of vast quantities of matter and radiation. Flares are known to occur often on our Sun, and can last anywhere from minutes to hours at a time.

When viewed from Earth through powerful telescopes, they serve as breath-taking reminders of the constant activity raging both on the surface, and deep within our parent star. As beautiful as these outbursts are, they also pose a significant threat to our way of life back here on Earth.

Following a solar flare, radiation cast off from the Sun's surface races outward through the solar system. If a flare happens to occur on an Earth-facing region of the Sun, the resultant stellar debris would strike our planet's protective barriers.

Depending on the power of the flare, this can result in a spectacular light show in the form of an aurora. However, on the more sinister side, the effects of a solar storm could cripple vital technological systems.

The most powerful Earth-facing solar flare in modern history erupted from the surface of the Sun back in 1859. In the intense geomagnetic storm that followed, which is now known as the Carrington Event, telegraph systems across the globe malfunctioned and sparked, and auroras were visible as far south as Cuba and Hawaii.

If a similar storm were to strike the Earth in the present day, it would affect countless vital technologies that are susceptible to electromagnetic disturbances, such as energy infrastructures and GPS satellites. To make matters worse, stellar bodies are capable of generating monstrous superflares that are far more powerful than the activity that sparked the Carrington Event.

Astronomers recently observed a dazzling white-light superflare emerging from an L dwarf star located roughly 250 light-years from Earth called ULAS J224940.13-011236.9. The authors of the study detailing the discovery estimate that the superflare erupted with the power of 80 billion megatons of TNT, making it 10 times more energetic than the 1859 Carrington event.

The scale and power of the flare is made all the more impressive by the fact that the star upon which it originated is so small that it barely qualifies to be called a star at all. ULAS J224940.13-011236.9 spans roughly a tenth of the radius of our Sun, giving it a volume close to that of the planet Jupiter.

Its relatively puny size places it in the transition region between fully fledged stars and brown dwarfs. The latter are essentially failed stars that were unable to accumulate enough mass to trigger the hydrogen fusion process that is currently raging deep within larger stellar bodies, including our own Sun.

Ordinarily, it would have been very difficult for most telescopes to pick out ULAS J224940.13-011236.9 from the starfield beyond due to its relatively low luminosity. However, upon unleashing the superflare, the L dwarf star briefly shone 10,000 times brighter than normal, making it an easy target for a number of ground based and orbital observatories.

"The activity of low mass stars decreases as you go to lower and lower masses, and we expect the chromosphere (a region of the star which support flares) to get cooler or weaker," comments lead author of the new study James Jackman, a PhD student in the University of Warwick's Department of Physics. "The fact that we've observed this incredibly low mass star, where the chromosphere should be almost at its weakest, but we have a white-light flare occurring shows that strong magnetic activity can still persist down to this level."

Whilst a superflare would likely have a devastating effect on the inhabitants of planet Earth, it could be instrumental to the emergence of life on planets orbiting cold L dwarf stars. Hotter stars are known to emit large amounts of ultraviolet (UV) radiation, whereas L dwarf stars throw out more radiation towards the infrared end of the spectrum. However, superflares are accompanied by a significant burst of UV radiation.

"To get chemical reactions going on any orbiting planets and to form amino acids that form the basis of life, you would need a certain level of UV radiation," says Jackman. "These stars don't normally have that because they emit mostly in the infra-red. But if they produced a large flare such as this one that might kick-start some reactions."

A paper detailing the discovery has been published in the Monthly Notices of the Royal Astronomical Society: Letters.

Source: University of Warwick

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