NASA’s Earth-orbiting NuSTAR telescope is usually used to peer at X-rays from high-energy events out in the universe like black holes and supernovae.
But recently, the agency decided instead to train its ultra-sensitive camera on the Sun – and the results are rather spectacular. As seen in blue in the image above, pointing NuSTAR at our Solar System’s star revealed high-energy X-rays from flares.
As NuSTAR is so sensitive, it cannot study X-rays from fully fledged solar flares, so these are actually smaller microflares, which are a million times weaker. Flares on the sun, which are eruptions of charged particles, form when magnetic field lines combine and break, and some are accompanied by ejections of material called Coronal Mass Ejections (CMEs). The relationship between the two is poorly understood.
"What's great about NuSTAR is that the telescope is so versatile that we can hunt black holes millions of light-years away and we can also learn something fundamental about the star in our own backyard," said Brian Grefenstette of the California Institute of Technology in Pasadena, an astronomer on the NuSTAR team, in a statement.
In the image, presented at the Royal Astronomical Society’s National Astronomy Meeting in Llandudno, Wales by Iain Hannah of the University of Glasgow, the other colors are from different telescopes. Green is from the X-ray Telescope instrument on Japan’s Hinode spacecraft, while yellow and red come from NASA’s Solar Dynamics Observatory (SDO).
Shown is the full image. Credit: NASA/JPL-Caltech/GSFC/JAXA
The Sun is now “quieting down” in its 11-year solar cycle according to Hannah, which means that there won’t be too many more opportunities to see events like this before it reaches its minimum activity in a few years.
However, one consequence is that it might be possible to see hypothesized nanoflares – eruptions that have one billionth of the energy of regular solar flares. It’s thought that these explosions may be the reason that the Sun’s corona – its outer atmosphere – is so much hotter than its surface.
NuSTAR could also be used to solve other solar mysteries, such as whether it is emitting dark matter particles known as axions, which has been suggested recently.