Solar flares are very energetic streams of protons, electrons, and ions which leave the Sun in bursts. They produce the auroras on Earth and can also interfere with our communications. Because the corona has a temperature of about 1,000,000 K, it's blackbody spectrum peaks in the X-ray. The Interstellar Medium Recall that the distance between stars is very large. But, this space is not empty.
Emission lines originate from the hot gas around young stars.
When these free electrons collide with the ionized hydrogen atoms, they recombine and the electrons cascade back down through the energy levels emitting light at discrete wavelengths. Such Emission Line Nebulae appear red in color because of the abundance of red wavelength emission lines on visible wavelength images. Even the neutral hydrogen gas that is away from young stars can produce emission line radiation, but in the radio part of the spectrum. This spectral line has a wavelength of 21 cm. The 21 cm line is produced by a spin-flip transition even though the atom is in its ground state.