The discovery of Seyfert galaxies dates back to 1908 when Edward A. Fath and Vesto Slipher observed the unusual emission lines of NGC 1068 at the Lick Observatory. This was a unique discovery as most observed celestial entities exhibited an absorption spectrum indicative of stars.
Making up around 10% of all galaxies, Seyfert galaxies are extensively studied in the field of astronomy. They share the same power source as quasars - supermassive black holes at their centres, surrounded by accretion discs. These discs are believed to emit the observed ultraviolet radiation. The composition of the surrounding material is best diagnosed via ultraviolet emission and absorption lines.
Interestingly, the majority of active galaxies, including Seyfert galaxies, are situated at great distances, exhibiting large Doppler shifts. This implies that they were more prevalent in the early universe and are now receding from the Milky Way due to cosmic expansion. Seyfert galaxies are closer than quasars, some of which are observed at distances of 12 billion light years. This means that observing these distant galaxies is akin to looking back in time.
Most Seyfert galaxies, when observed in visible light, resemble regular spiral galaxies. However, studies across other wavelengths reveal that their core's luminosity is comparable to the entire luminosity of galaxies the size of the Milky Way. This observation significantly contributes to our understanding of galactic evolution and the role of active galactic nuclei.
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