Anne’s Image of the Day: Barred Spiral Galaxy UGC 12158

June 17, 2014

UGC 12158, a barred spiral galaxy in Pegasus

Image Credit: ESA/Hubble & NASA

UGC 12158 is a barred spiral galaxy of about 140,000 light-years across, located some 400 million light-years away from Earth in the northern constellation of Pegasus (the Winged Horse). It is speeding away from us at approximately 9,289 kilometers per second. This galaxy looks like our Milky Way’s identical twin in its structure, only it is almost 40% (!!) larger than our home galaxy, so it is really huge.

UGC 12158 is an excellent example of a barred spiral galaxy. Barred spirals, as the name suggest, feature spectacular swirling arms of stars that emanate from a bar-shaped center. Such bar structures are common, being found in about two thirds of spiral galaxies, and are thought to act as funnels, guiding gas to their galactic centers where it accumulates to form newborn stars. These aren’t permanent structures: astronomers think that they slowly disperse over time, so that the galaxies eventually evolve into regular spirals.

In this image we can also see a bright blue star just to the lower left of the center of the galaxy. This star is in fact a Type Ia supernova, called SN 2004ef, which was first spotted by the two British amateur astronomers Mark Armstrong and Tom Boles on September 4, 2004. The Hubble data shown here form part of the follow-up observations.

A Type Ia supernova is a result from the violent explosion of a white dwarf star (a compact star that has ceased fusion in its core). The white dwarf increases its mass beyond a critical limit (the Chandrasekhar limit) by gobbling up matter from a companion star. A runaway nuclear explosion then makes the star suddenly as bright as a whole galaxy, before gradually fading from view.

This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through blue (F475W, coloured blue), yellow (F606W, coloured green) and red (F814W, coloured red) as well as a filter that isolates the light from glowing hydrogen (F658W, also coloured red) have been included. The exposure times were 1160 s, 700 s, 700 s and 1200 s respectively.