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Our Sun was both active and ’feisty’ in its infancy, growing in fits and starts while burping out bursts of X-rays, scientists say.
Scientists have reached this conclusion by studying the young star TW Hydrae, located about 190 light-years from Earth in the southern constellation Hydra the Water Snake.
“By studying TW Hydrae, we can watch what happened to our Sun when it was a toddler,” said Nancy Brickhouse of the Harvard-Smithsonian Center for Astrophysics (CfA).
TW Hydrae is an orange, type K star weighing about 80 per cent as much as our Sun. It is about 10 million years old, and is still accreting gas from a surrounding disk of material.
That same disk might contain newborn planets.
In order to grow, the star “eats” gas from the disk.
However, the disk does not extend all the way to the star’s surface, so the star cannot dine from it directly. Instead, infalling gas gets funnelled along magnetic field lines to the star’s poles.
Infalling material smashes into the star, creating a shock wave and heating the accreting gas. The gas glows with high-energy X-rays. As it continues moving inward, the gas cools and its glow shifts to optical wavelengths of light.
To study the process, Brickhouse and her team combined observations from NASA’s Chandra X-ray Observatory with those from ground-based optical telescopes.
“By gathering data in multiple wavelengths we followed the gas all the way down. We traced the whole accretion process for the first time,” explained Brickhouse.
They found that accretion was clumpy and episodic in building a star. At one point the amount of material landing on the star changed by a factor of five over the course of a few days.
Some of the infalling material is pushed away in a stellar wind much like the solar wind that fills our solar system.
Some gets channelled into giant loops and stellar prominences.
Astronomers have known that young stars are much more magnetically active than our middle-aged Sun, but now they can actually probe the interplay between the star’s magnetic fields and the protoplanetary disk.
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