Nasa’s Solar Dynamics Observatory (SDO) has observed a massive eruption on the Sun — one of the biggest in years. The footage, recorded on 19 April, is not only dramatic, but also could solve a longstanding mystery about coronal rain…
Astronomers have seen eruptions like this before, but rarely so large and never in such fluid detail. One can see a billion tons of magnetised plasma blasting into space while debris from the explosion falls back onto the Sun surface.
The first half of this video shows a magnetic filament erupting. The black "hair-like object" is a speck of dust on the CCD camera.
Coronal rain has long been a mystery. It's not surprising that plasma should fall back to the Sun. After all, the Sun's gravity is powerful. The puzzle of coronal rain is how slowly it seems to fall. Said Karel Schrijver of Lockheed Martin's Solar and Astrophysics Lab: "The Sun's gravity should be pulling the material down much faster than it actually moves. But what's slowing the descent?"
For the first time, SDO provides an answer.
"The rain appears to be buoyed by a 'cushion' of hot gas," says Schrijver. "Previous observatories couldn't see it, but it is there."
One of SDO's game-changing capabilities is temperature sensing. Using an array of ultraviolet telescopes called the Atmospheric Imaging Assembly (AIA), the observatory can remotely measure the temperature of gas in the Sun's atmosphere. Coronal rain turns out to be relatively cool — "only" 59 700 degrees Celsius. When the rains falls, it is supported, in part, by an underlying cushion of much hotter material, between 999 700 and 2199 700 degrees Celsius.
The second half of the video: one can see the hot gas in this colour-coded temperature movie. Cool material is red, hotter material is blue-green. The hot gas effectively slows the descent of the coronal rain.
* News: SDO observes massive eruption, scorching rain on Sun