Sun's Eruption Offers Insight to the Evolution of Stars

A new look at the plasma eruption and subsequent splashdown that took place on the surface of the Sun during the summer of 2011 reveals how the event, caught in dramatic detail by NASA's Solar Dynamics Observatory, may provide insights into the evolution of stars.

The spacecraft, which never lifts its steady eye away from the Sun, provides images with better-than-HD resolution and contains an Atmospheric Imaging Assembly instrument designed and developed by researchers at the Harvard-Smithsonian Center for Astrophysics (CfA).

As a result, the images caught at the time of the eruption, scientists say, may offer a glimpse at how young stars grow by sucking up nearby gas.

"We're getting beautiful observations of the Sun," CfA astronomer Paola Testa said in a press release. "And we get such high spatial resolution and high cadence that we can see things that weren't obvious before."

In the movies taken of the event, scientists are able to watch dark filaments of gas blasting outward from the Sun's lower right region, which, though it appears dark against the star's bright surface, actually glows at a temperature of some 18,000 degrees Fahrenheit.

When the blobs of plasma hit the Sun's surface again, they heat up by a factor of 100 to a temperature of almost 2 million degrees Fahrenheit.

As a result, those spot brighten in the ultraviolet by a factor between two and five in a matter of minutes.

Such a tremendous release of energy occurs because the in-falling blobs are traveling at speeds reaching 900,000 miles per hour, similar to the speeds reached by material falling onto young stars as they grow by accretion. Therefore, scientists deduce, watching the solar eruption may provide an "up close" view of what is occurring on distant stars.

"We often study young stars to learn about our Sun when it was an 'infant,'" Testa explained. "Now we're doing the reverse and studying our Sun to better understand distant stars."

These observations, combined with computer modeling, have helped resolve a decade-long argument over how to measure the accretion rates of growing stars.

Astronomers calculate how fast a young star gathers material by observing its brightness at various wavelengths of light and how its brightness changes over time. However, a discrepancy arose when researchers compared the estimates from optical and ultraviolet light compared with X-rays.

By determining that the ultraviolet flashes they observed came from the in-falling material itself, rather than the surrounding solar atmosphere, scientists decided that, should this be true for young stars, then by analyzing the ultraviolet light they emit, they can learn about the material they are accreting.

"By seeing the dark spots on the Sun," Testa said, "we can learn about how young stars accrete material and grow."