This rotating image shows the bright spiral galaxy known as MCG-01-24-014, located about 275 million light-years from Earth. MCG-01-24-014, in addition to being a well-defined spiral galaxy, has an extremely energetic core known as an active galactic nucleus (AGN) and is a type 2 Seyfert galaxy.

Seyfert galaxies, along with quasars, comprise one of the most common subclasses of GNSS. Although precise classification of NGNs requires nuance, Seyfert galaxies tend to be relatively close and their central NGNs do not eclipse the host; Quasars, on the other hand, are very distant NGNs with incredible brightness that dwarf their parent galaxies.

There are other subclasses of both Seyfert galaxies and quasars. In the case of Seyfert galaxies, the dominant subcategories are Type 1 and Type 2. Astronomers separate them by their spectrum, which is the structure that results when light is divided into wavelengths. The spectral lines emitted by Type 2 Seyfert galaxies are associated with certain “forbidden” emission lines. To understand why galactic radiation might be banned, you need to understand why spectra exist.

Spectra appear this way because certain atoms and molecules absorb and emit very specific wavelengths of light. The reason for this is quantum physics: Electrons (tiny particles orbiting around the nucleus of atoms and molecules) can only exist at very specific energies, and therefore electrons can only lose or gain very specific amounts of energy. These very specific amounts of energy correspond to the wavelengths of light that are absorbed or emitted.

According to certain rules of quantum physics, forbidden emission lines should not exist. But quantum physics is complex, and some of the rules used to predict it were formulated in laboratory conditions here on Earth. Under these rules, this type of radiation is so unlikely to be “forbidden” that it is ignored. But in space, in the incredibly energetic core of the galaxy, these assumptions are no longer true, and “forbidden” light gets the chance to illuminate us.