Canis Major Dwarf - Milky Way's Latest Conquest

The dwarf galaxy is located in the center of Canis Major, the constellation that's home to the Dog Star - Sirius, the brightest star in the night sky. To the ancient Greeks, Canis Major, in particular Sirius, represents a hunting dog following Orion, helping the hunter in pursuit of Lepus the Hare.

Discovered just recently in 2003 by an international team of astronomers from France, Italy, the UK, and Australia, the Canis Major Dwarf is only 25,000 light years away from earth. Just across town by comparison to Sagittarius at 50,000 light years from earth. The team sifted though data on millions of stars collected by 2MASS (the Two-Micron All Sky Survey) and discovered an unusually dense area of M Giants (a class of star). The 2MASS survey scanned the entire sky at three near-infrared wavelengths with 1.3-meter telescopes in Chile and Arizona to "look through" clouds of dust and gas in our Milky Way Galaxy to get a clearer, more accurate picture of it's makeup.

The Canis Major Dwarf, classified as an irregular galaxy, went undetected for many years because of this dust in the Milky Way's atmosphere. The decaying galaxy lies very close to our galaxy's galactic plane where it's most dense and difficult to see and was hidden from view with normal viewing methods.

If you're wondering how they can measure the distance of something that's so far away, astronomers have found that M Giants of a given infrared color have nearly the same luminosity. With knowledge of a stars' mass, they can calculate its true luminosity, or how bright it would appear if it was nearby. The difference between the true luminosity and the observed luminosity gives the distance between the stars and Earth. You know they stayed up late a few nights figuring that one out!

Computer simulations show this galaxy is being torn apart by our galaxy's gravitational pull and remnants are slowly merging to become part of the Milky Way. At one time it's believed to have contained about one billion stars but has, over the course of a billion years or so, been gobbled up by our galaxy contributing a relatively significant amount to the Milky Way's matter (about 1 percent). That the Milky Way has been growing by devouring smaller galaxies has been a consensus among astronomers for years and this discovery definetly supports that assumption. It suggests that the Milky Way is still growing and not middle-aged as contended by some. Middle aged or infancy, the Milky Way will last a lot longer than hundreds of generations of humans on Earth.

The team also believes there must be remnants of other galaxies dotted throughout the Milky Way but they would be nearly impossible to detect because of an advanced state of decay and without more details from the Canis Major Dwarf's destruction.

The discover is of interest to another team of astronomers from the Rensselaer Polytechnic Institute. They found a ring of stars encircling the Milky Way and theorized that its origin was in fact the disruption of a galaxy that drifted too close to our own. They are excited to hear of this new dwarf's fate because it supports their theory.

About The Author-- Ron Berry is an amateur astronomer and freelance journalist who writes for Essay Street - For astronomy news and other stories visit ScopeDoggie

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