Candles flickering on the solar surface
Swedish 1-m Solar Telescope
On September 21, 1915, while observing the Sun at Mount Wilson Solar Observatory in the USA, Ferdinand Ellerman saw an intense brightening in solar spectra. He wrote: "On the first occasion the appearance was so extraordinary that it seemed hardly real; after the second observation, however, the existence of such phenomena as part of the solar activity seemed established". Because these features were so prominent in the spectra of hydrogen lines, he named them “solar hydrogen bombs". Today we call them "Ellerman bombs" or just "EBs".
These features are common part of flux emergence. They occur repetitively in young emerging active regions, last for few minutes and then disappear. When we look at them with today's instrumentation and sample wings of the H-alpha line, they appear as candles that flicker at the solar surface, sometimes with multiple flames. They are as long as 1000 km and almost always point towards the solar limb.
It took us exactly 100 years to explain what they really are. Thanks to numerical simulations, we can now say with certainty that these are locations where magnetic field reconnects and magnetic energy is converted to kinetic and thermal energy. During the reconnection, hot pockets of plasma are formed, which we then see as elongated flame-like features when we look at them from certain perspectives. They mark the location where heavy material that emerges from inside the Sun, gets rid of much of its mass and becomes free to expand further towards the upper solar atmosphere.
Although we have learned a lot about the nature of EBs in the past few years, a lot still stays unclear. The European Solar Telescope will enable us to look at these features in more detail and discover more about their properties and the underlying physical process.
The first part of the movie presents observations obtained with the CRISP instrument at the Swedish 1-m Solar Telescope on La Palma (Spain) showing EBs as flames close to the solar limb in the red wing of the H-alpha spectral line. The second part of the movie shows simulations of the emergence of a magnetic sheet into the solar surface. Color lines denote magnetic field lines as they emerge and reconnect. The green areas are hot regions which correspond to the flames we observe. The animation was made using the NCAR Vapor visualization software.
To download the movie, right click HERE
Movie credit: Sanja Danilovic (ISP/Stockholm)
Observations: Gregal Vissers and Eamon Scullion (ITA, University of Oslo)
Simulations: Sanja Danilovic (ISP/Stockholm)