Hubble Examines a Galaxy of the Late Type

About 85 million light-years away from Earth, NGC 2814 is an irregular galaxy that can be seen in this image taken with the NASA Hubble Space Telescope. The galaxy appears to be fairly isolated in this image, which was taken with Hubble’s Advanced Camera for Surveys. It resembles a haphazardly applied bright paint stroke on a dark background. But appearances can be deceiving. In fact, NGC 2814 has three close-by (astronomically speaking) neighboring galaxies that are not visible in this picture: NGC 2820, a side-on spiral galaxy; IC 2458, an irregular galaxy; and NGC 2805, a face-on non-barred spiral galaxy. The four galaxies together comprise the galaxy group known as Holmberg 124. Sometimes, a collection of these galaxies is referred to as “late-type galaxies.”

“Early-type” describes elliptical galaxies, whereas “late-type” refers to spiral and irregular galaxies. The astronomy community has a widespread misconception as a result of this rather perplexing terminology. A common misconception persists in the belief that Edwin Hubble classified elliptical galaxies as early-type and spiral and irregular galaxies as late-type galaxies because ellipticals were the evolutionary forerunners of spiral and irregular galaxies.

This misperception stems from the Hubble tuning fork of galactic classification, which graphically depicts galaxy types moving from spiral to elliptical in a series that is readily understood to represent a temporal evolution. Hubble did not intend to imply that elliptical galaxies were the direct evolutionary progenitors of spiral and irregular galaxies; rather, he adopted the terms early-type and late-type from much older astronomical terminology for characterizing stars. Indeed, he stated clearly that “the nomenclature… [early and late]… refers to position in the sequence, and temporal connotations are made at one’s ” in a 1927 paper.

The misperception endures nearly a century after Hubble’s strongly worded discussion on the subject, which may serve as a useful illustration of the benefits of categorizing things using simple terms right away!