nov 272013

November 27, 2013

NGC 3982, a spiral galaxy in Ursa Major

UGC 6918

Image Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA); Acknowledgment: A. Riess (STScI)

NGC 3982 (also known as UGC 6918) is an intermediate spiral galaxy of some 30,000 light-years across, located approximately 68 million light-years away in the constellation of Ursa Major (the Great Bear), while it is receding from us at about 1109 kilometers per second. It is a member of the M109 Group, a group that contains over 50 galaxies.

Although it is about one-third of the size of our Milky Way galaxy, NGC 3982 is a typical spiral galaxy, quite similar to our own Milky Way. Its spiral arms are filled with bright stars, blue star clusters, massive pink star-forming regions of glowing hydrogen, and obscuring dust lanes that provide the raw material for future generations of stars. It harbors a supermassive black hole at its core.

NGC 3982 has a high rate of star birth within its spiral arms, and has also active star formation in the circumnuclear region, estimated at 0.52 solar masses per year. Its bright nucleus is home to older populations of stars, which grow more densely packed toward the center.

This image shows a mini-spiral between the circumnuclear star-forming region and the galaxy’s nucleus, which could be the channel through which gas is transported to the supermassive black hole from the star-forming region.

In April 1998, a Type Ia supernova – later called SN 1998aq – was discovered in NGC 3982 by British amateur astronomer Mark Armstrong. It was discovered when it had an apparent magnitude of 14.9 and it had grown considerably brighter by two days after its initial sighting (it reached a maximum magnitude of 14.0). The explosion resulted from a binary system where a white dwarf star was capturing mass from its companion star. When the white dwarf had gathered enough mass and was no longer able to support itself, the star detonated in a violent and extremely bright explosion.

At an apparent magnitude of 12.0, this face-on galaxy needs a telescope to be viewed. Using small telescopes, the galaxy appears as a very faint, diffuse patch of light with its central region appearing as a slightly brighter diffuse ball.

This color image is composed of exposures taken by the Hubble Space Telescope’s Wide Field Planetary Camera 2 (WFPC2), the Advanced Camera for Surveys (ACS), and the Wide Field Camera 3 (WFC3). The observations were taken between March 2000 and August 2009. The rich color range comes from the fact that the galaxy was photographed in visible and near-infrared light. Also used was a filter that isolates hydrogen emission that emanates from bright star-forming regions dotting the spiral arms.

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