A dwarf galaxy with double identity

By Kathy Li
August 27, 2017


Image Credit: Nasa

On November 3, 1885 (that’s 132 years ago), American astronomer Ormond Stone discovered a dwarf galaxy -- a diminutive, starburst galaxy dubbed NGC 178. The NGC 178 is a spiral galaxy in the constellation of Cetus.

Unfortunately, at the time, the galaxy’s position was recorded incorrectly. As a result of the mistake, the area where NGC 178 should have been was still deemed unoccupied.

Some years later, French astronomer Stéphane Javelle spotted NGC 178 in the sky. Believing that he had discovered a new galaxy, Javelle published it in the Index Catalog under a new name -- IC 39.

New General Catalog

In case you were wondering: NGC represents the New General Catalog of Nebulae and Clusters of Stars -- a catalog of deep-sky objects compiled by Danish-Irish astronomer John Louis Emil Dreyer in 1888.

NGC is the new version of Sir John Herschel's General Catalog of Nebulae and Clusters of Stars. The NGC contains 7,840 objects, which are also known as the NGC objects. It is one of the largest comprehensive catalogues, as it includes all types of deep-space objects and is not confined to, say, galaxies.

Dreyer also published two supplements to the NGC in 1895 and 1908, known as the Index Catalogs, describing a further 5,386 astronomical objects.

Now what about IC?

Index Catalog

The Index Catalog of Nebulae and Clusters of Stars (abbreviated as IC) is the first major update to the NGC, published in two parts by Dreyer in 1895 (IC I, containing 1,520 objects) and 1908 (IC II containing 3,866 objects). It serves as a supplement to the NGC, and contains an additional 5,386 objects, collectively known as the IC objects. It summarizes the discoveries of galaxies, clusters and nebulae between 1888 and 1907, most of them made possible by astronomical photography. A list of corrections to the IC was published in 1912.

So what ends up happening to the double-named galaxy?

When American astronomer Herbert Howe observed the galaxy, he was able to identify and correct Stone’s initial mistake made on its position.

It wasn’t until many years later that astronomers realized that both NGC 178 and IC 39 referred to the same object!

With a diameter of approximately 40,000 light-years, the NGC 178 is much smaller than the Milky Way. Hence its classification as a dwarf galaxy. Nevertheless, it is known to be forming new stars left, right, and center! That is why it is also labelled as a starburst galaxy.

In the New General Catalog, John Louis Emil Dreyer noted that the NGC 178 was "faint, small, much extended 0°, brighter middle" -- a description that matches what we can see in the following picture quite nicely!

NGC 178

This image of NGC 178 comprises data gathered by the Wide Field Planetary Camera 2 aboard the NASA/ESA Hubble Space Telescope. (Image Credit: ESA/Hubble & NASA)

Other than that, not much further information of the dwarf galaxy has been unearthed yet. What with its double identity and all, I couldn’t help but wonder: If there were any intelligent living creatures in the NGC 178, what would they name us? What name would they give the Milky Way -- the galaxy in which our Earth is located?