Up Close: Dwarf Galaxy NGC 147 in Cassiopeia | Hubble Space Telescope

Up Close: Dwarf Galaxy NGC 147 in Cassiopeia | Hubble Space Telescope

NGC 147, also known as Caldwell 17, is a dwarf galaxy located roughly 2.5 million light-years from Earth. It is a member of the Local Group of galaxies. It is dominated by our Milky Way and the Andromeda galaxy. NGC 147, like its neighbor NGC 185, is a distant satellite of the Andromeda galaxy. Just as the planets in the solar system are gravitationally bound to the Sun, so are these smaller galaxies bound to their much more massive galactic host. While many classes of galaxies can exist as satellites, dwarf spheroidal galaxies (small, dim, spherical-shaped galaxies) like NGC 147 have been observed in this role more frequently than any other type of galaxy.

Dwarf satellite galaxies tend to appear very diffuse and dim, so they can be difficult to spot (especially in light-polluted or hazy skies). NGC 147 is no exception. It has an apparent magnitude of 9.5, and observers will need a small telescope set up in a dark location to detect the faint galaxy. NGC 147 is located in the southern edge of the constellation Cassiopeia, between the constellation’s “W” pattern and the Andromeda galaxy. (The neighboring NGC 185 is brighter and less diffuse, so it is easier to see.) The best time of year to spot NGC 147 from the Northern Hemisphere is the autumn. It can also be seen in northern latitudes of the Southern Hemisphere in the spring. The galaxy was discovered by the English astronomer John Herschel in September of 1829.

This image of NGC 147 is a composite of observations made in visible and infrared light by Hubble’s Wide Field Camera 3. The image captures an area near the core of the galaxy, notable for its elderly stellar population. Astronomers used Hubble’s observations to investigate the properties of NGC 147’s many globular star clusters.

Image Credit: NASA, ESA, and A. Ferguson (University of Edinburgh, Institute for Astronomy)

Image Processing: Gladys Kober (NASA/Catholic University of America)
Date: June 26, 2020

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