Tuesday, October 13, 2009

NGC 2623's Galactic Merger

NGC 2623 is one of those deep-sky objects recorded in the 19th-century compendium called “A New General Catalogue of Nebulae and Clusters of Stars,” or for short, the “New General Catalogue” (NGC). Danish-Irish astronomer J. L. E. Dreyer published the NCG for the Royal Astronomical Society using primarily the recorded observations from William Herschel, is son, John Herschel.

NGC 2623, as recently imaged by ESA/NASA Hubble Space Telescope. Image Credit: ESA/NASA

The object NGC 2623 is located in the direction of the constellation Cancer, the Crab, about 250 million light-years away. When viewed in dark skies with a medium-sized telescope, with about a 12-inch aperture or so, the object has a strange, swirling shape. It has the appearance of a bird flying head-on at the observer, with one wing sweeping up, the other wing sweeping down, and the main mass of the body clumped in the center. This object is a galaxy. Or more accurately, two galaxies which are still in the process of merging into one.

Over the last century of study, astronomers have learned that it is not so uncommon for galaxies to collide and merge into larger galaxies. In fact, our own Milky Way galaxy has a date with the Andromeda galaxy in about 3 billion years. But that's another story…

Galaxies that merge do not just bump into each other. They contain lots of space between their stars, after all. But the interaction process does have a dramatic effect on each of the galaxies. Studies show that as galaxies approach one another massive amounts of gas are pulled from each galaxy toward the center of the other, until the two ultimately merge into one massive galaxy. NGC 2623 is in the late stages of the merging process. The centers of the original galaxies are combined, but stretching out from the center are two curling tails of young stars—these are the “wings” I referenced in my shape description earlier. The curling tails are a telltale sign that a galactic merger has occurred. During one of these mergers, the dramatic exchange of mass and gases initiates the process of star formation. The young stars visible in the two tails were created by this process.

Some of the galactic mergers, like that of NGC 2623, can result in an active galactic nucleus, where one of the super-massive black holes—from the center of one of the two original galaxies—is stirred into action. Matter is pulled toward the black hole, forming an accretion disc. The energy released by this activity heats up the disc, causing it to emit across a wide range of the electromagnetic spectrum.

NGC 2623 is so bright in the infrared that it has become a member of the group of very luminous infrared galaxies (LIRG) and it has been extensively studied as the part of the Great Observatories All-sky LIRG Survey (GOALS) project. The GOALS project combines data from some of the most advanced space-based telescopes, including Hubble. Additional data from infrared and X-ray telescopes can further characterize objects like active galactic nuclei and nuclear star formation by revealing what is unseen at visible wavelengths.

The GOALS project includes data from NASA/ESA's Hubble Space Telescope, NASA's Spitzer Space Telescope, NASA's Chandra X-ray Observatory and NASA's Galaxy Evolution Explorer (GALEX). The joint efforts of these powerful observing facilities have provided a clearer picture of our local Universe. To learn more about NGC 2326 and the Hubble Space Telescope, check out these links:

NGC 2326, at the European Home Page for the NASA/ESA Hubble Space Telescope

NASA’s Home Page for the Hubble Space Telescope

The Space Telescope Science Institute (STScI)


No comments: