June 21, 2013
Young Stars Grow By Consuming Nearby Gas
April Flowers for redOrbit.com - Your Universe Online
Our Sun erupted on June 7, 2011, sending tons of hot plasma blasting into space. Some of the plasma fell back to the surface of the Sun, sparking bright flashes of ultraviolet light. A new study from the Harvard-Smithsonian Center for Astrophysics (CfA) examines the dramatic event to provide new insights into how young stars grow by consuming nearby gas.NASA's Solar Dynamics Observatory captured the eruption and subsequent splashdown in spectacular detail. Watching the Sun 24 hours a day, the spacecraft provides images with better-than-HD resolution using its Atmospheric Imaging Assembly instrument that was designed and developed by the team at CfA.
"We're getting beautiful observations of the Sun. And we get such high spatial resolution and high cadence that we can see things that weren't obvious before," said CfA astronomer Paola Testa.
Dark filaments of gas are seen blasting outward from the Sun's lower right in movies of the eruption. The solar plasma appears dark against the Sun's surface in the movies. In reality, however, it glows at a temperature of approximately 18,000 degrees Fahrenheit. That temperature rises by a factor of 100, to nearly 2 million degrees Fahrenheit, as the blobs of plasma splash down on the Sun's surface. In the ultraviolet spectrum, those superheated blobs brighten by a factor of 2 -5 in just a few minutes.
The in-falling blobs are traveling at extremely high speeds, up to 900,000 miles per hour, which causes the enormous energy release to occur. The speed of these blobs is similar to the speeds reached by material falling into young stars as they grow via accretion, making the observations of the solar eruption an "up close" view of what occurs on distant stars.
"We often study young stars to learn about our Sun when it was an 'infant.' Now we're doing the reverse and studying our Sun to better understand distant stars," notes Testa.
Combined with computer modeling, these new observations have helped resolve a ten year debate over how to measure the accretion rate of growing stars. How fast a young star is gathering material is calculated by observing its brightness at various wavelengths of light, and how that brightness changes over time. The scientists obtained higher estimates from optical and ultraviolet light than from X-rays.
The ultraviolet flashes observed came from the in-falling material itself, the team discovered, not the surrounding solar atmosphere. They suggest that if the same holds true for distant, young stars, analyzing the ultraviolet light emitted can teach us about the material being accreted.
"By seeing the dark spots on the Sun, we can learn about how young stars accrete material and grow." explained Testa.