Seyfert, Carl Keenan (1911–1960)

US astronomer and astrophysicist who studied the spectra of stars and galaxies, and identified and classified the type of galaxy that now bears his name.

Seyfert was born in Cleveland, Ohio, and studied at Harvard University, Cambridge, Massachusetts. He graduated from Harvard with a BSc in 1933, gaining an MA in 1935 and a PhD in 1936. He was director of Barnard Observatory, Oxford, Mississippi, 1946–51, and from 1951 professor of astronomy at Vanderbilt University, Nashville, Tennessee, and director of the Arthur S Dyer Observatory. He was a member of the National Defence Research Committee.

In 1943, Seyfert was studying 12 active spiral galaxies with bright nuclei. His investigations showed that these galaxies contain hydrogen as well as ionized oxygen, nitrogen, and neon. On the basis of their spectra, Seyfert divided the galaxies into two types, I and II. Seyfert galaxies emit radio waves, infrared energy, X-rays, and nonthermal radiation. The gases at their centres are subject to explosions which cause them to move violently, with speeds of many thousands of kilometres per second relative to the centre of the galaxy in the case of type I, and of several hundreds of kilometres per second in the case of type II.

In 1951, Seyfert began a study of the objects now known as Seyfert's Sextet: a group of diverse extragalactic objects, of which five are spiral nebulae and one an irregular cloud. One member of the group is moving away from the others at a velocity nearly five times that at which the others are receding from each other.