Friday, March 6, 2015

What is the closest Galaxy to the Milky Way?

By Matt Williams via Universe Today, 4 March 2015

Illustration of the Canis Dwarf Dwarf Galaxy and its associated tidal (shown in red) in relation to our Milky Way. Credit: R. Ibata (Strasbourg Observatory, ULP) et al./2MASS/NASA

Scientists have known for some time that the Milky Way Galaxy is not alone in the Universe. In addition to our galaxy being part of the Local Group — a collection of 54 galaxies and dwarf galaxies — we are also part of the larger formation known as the Virgo Supercluster. So you could say the Milky Way has a lot of neighbors.

Of these, most people consider the Andromeda Galaxy to our closest galactic cohabitant. But in truth, Andromeda is the closest spiral galaxy, and not the closest galaxy by a long shot. This distinction falls to a formation that is actually within the Milky Way itself, a dwarf galaxy that goes by the name of the Canis Major Dwarf Galax (aka. the Canis Major Overdensity).

This stellar formation is about 42,000 light years from the galactic center, and a mere 25,000 light years from our Solar System. This puts it closer to us than the center of our own galaxy, which is 30,000 light years away from the Solar System.

Prior to its discovery, astronomers believed that the Sagittarius Dwarf Galaxy was the closest galactic formation to our own. At 70,000 light years from Earth, this galaxy was determined in 1994 to be closer to us than the the Large Magellanic Cloud (LMC), the irregular dwarf galaxy 180,000 light years away which previously held the title of our closest neighbor.

Image showing nearly 50,000 galaxies in the nearby universe detected by the Two Micron All Sky Survey (2MASS) in infrared light. Credit: 2MASS/T. H. Jarrett/J. Carpenter/R. Hurt

All of that changed in 2003 when The Canis Major Dwarf Galaxy was discovered by the Two Micron All-Sky Survey (2MASS), a collaborative astronomical mission that took place between 1997 and 2001.

Using the telescopes located at the Mt. Hopkins Observatory in Arizona (for the Northern Hemisphere) and the Cerro Tololo Inter-American Observatory in Chile for the southern hemisphere, astronomers were able to conduct a comprehensive survey of the sky in infrared light, which is not blocked by gas and dust as severely as visible light.

Because of this technique, the astronomers were able to detect a very significant over-density of class M giant stars in a part of the sky occupied by the Canis Major constellation, along with several other related structures composed of this type of star, two of which form broad, faint arcs (as seen in the image at top).

The prevalence of M-class stars is what made the formation easy to detect. These cool, “Red Dwarfs” are not very luminous compared to other classes of stars, and cannot even be seen with the naked eye. However, they shine very brightly in the infrared, and appeared in great numbers.

Continue to the full article,

No comments: