White Light Stellar Flares

A major solar eruption is shown in progress October 28, 2003

New data from NASA’s Kepler space telescope is allowing astronomers a glimpse at potentially catastrophic flaring in a solar-type star roughly 300 light years away.

The observations detail some of the largest flaring events ever detected from a fully-mature G spectral-type star, known for now by its Kepler Input Catalog number KIC 11551430. Flaring from the star is several thousands times stronger than the Carrington Event — a September 1859 solar super-flare, hundreds of times stronger than most of our Sun’s “X-class” flares (the most powerful solar flares yet classified).

We are counting thousands of white light flares from KIC 11551430 in a range from 10 to 10,000 times bigger than the biggest flares produced by our own Sun, Rachel Osten, an astronomer at the Space Telescope Science Institute and the team leader on the Kepler survey of this star, told Forbes.

“When you count and plot these really energetic stellar flares,” said Osten, “you expect to have more and more energetic flares happening less and less frequently.”

The fact that we see a limit on the flare energies for these stars, Osten says, “sort of” confirms that these flares get their energy from star spots, or magnetic fields poking through the stellar surface.

In the mid-19th century, x-ray measurements of the Carrington Event weren’t yet available. But because the superflare was associated with spectacular Earth auroras, Osten says the event was likely coupled with a coronal mass ejection (or CME) — a magnetized plasma streaming high-energy accelerated particles at thousands of kilometers per second.

Osten says our own Sun might still be capable of producing something slightly larger than the Carrington Event which, at the time, sent the new technology of the telegraph into a tailspin.

But in its 4.5 billion year history, has the Sun ever produced a flare 10,000 times larger than the Carrington Event? 

“Almost certainly, yes,” said Osten. “During its first hundred million years, the Sun was very active.”
Osten says a close binary stellar companion in which two stars are gravitationally interacting might explain why KIC 11551430, located in the bright constellation of Cygnus, is so active. She says that when two stars are that close, tidal forces cause their rotation and orbital period to be coupled with each other. As a result, a star with a close binary companion will rotate much faster than if it were simply a single star.

David Soderblom, a staff astronomer at the Space Telescope Science Institute and one of the Kepler team members, told Forbes that if indeed this star does have a stellar binary companion, this putative companion likely orbits KIC 11551430 only every 5.2 days.  That’s much closer than Mercury orbits our own Sun. However, Soderblom is quick to point out that no planets have been detected around the star. And even if planets were orbiting both these putative stellar binary companions in what he terms “circumbinary” orbits, he says they would still be extremely difficult to spot via current planet detection methods.

But for argument’s sake, what would happen if an Earth-like planet around one of these stars got in the path of one of these extremely high-energy white light flares?

“Solar flares on our own Sun [produce] a CME,” said Osten. As Osten explains, flares in conjunction with a CME can act as part of an enhanced stellar wind that can compress a planet’s magnetosphere and expose a portion of its atmosphere to the effect of ionizing radiation.

In a period of a few years, energetic particles associated with the flare would strip the ozone layer from the planet, exposing the surface to ultraviolet (UV) radiation from our sun as solar light. Osten says it would then probably only be a matter of months before any inhabitants were killed off.

“On this star, this flaring is happening every week,” said Osten. “We’re trying to determine if CMEs accompany large flares. We haven’t seen them.”
But if the extreme flares that we see for these very active stars are accompanied by CMEs, then Osten says that would be an impediment for life being able to develop on one of the star system’s hypothetical nearby habitable planets.

And although no one is suggesting something similar could happen to our own star, our Sun is still capable of Carrington-type events of the sort that could wreak havoc on today’s satellite communication systems.

“No matter how closely we study our Sun, it remains just one star,” said Soderblom.  “In terms of real knowledge and behavior, at most, our [understanding] of the Sun only goes back half a century.”

But by observing hundreds of thousands of other stars, Soderblom says we can gain context for “what the Sun does” in a way that the Sun itself “will never tell us.”

Cr.Forbes, Solar Lamp