Astronomers have discovered that a strange ring of distant stars may actually be part of our galaxy, making it 50% bigger at 150,000 light-years wide. This is based on re-analysis of a distant ring that surrounds our galaxy, which the astronomers think is now actually part of the Milky Way.
The team of scientists from Rensselaer Polytechnic Institute in New York studied the Monoceros Ring, which is a long ring-like filament of stars that ‘wraps’ around our galaxy three times. It is located 65,000 light-years from our galaxy’s centre, and in total is 200,000 light-years in length. Previously it was thought to be a stream of stars torn from the nearby Canis Major Dwarf Galaxy due to interactions with the Milky Way. Now, however, it seems that the ring may actually be part of our own galaxy, and could have been disturbed by other dwarf galaxies. ‘It looks to me like maybe these patterns are following the spiral structure of the Milky Way, so they may be related,’ Dr Heidi Newberg, from the Rensselaer Polytechnic Institute in New York. ‘It now looks to me like it’s part of the disk,’ she added.
In this image, we estimate the stellar density of stars 8 kpc away from the sun. The image is in galactic coordinates, and the plane of the Milky Way is clearly visible, although some areas are too crowded with stars or obscured by dust to be measured accurately. Between longitude 8 hours and 16 hours, there is a grey, wispy cloud that extends 30 degrees (4 kpc: white patch) away from the galactic plane in either direction. This is the Monoceros Ring. The high density of stars so far away from the plane of the galaxy is not explained by simple galactic models. Note that because the image is not in galctocentric coordinates, we would not expect to the Monoceros Ring wrap all the way around the image even if it does wrap around the Milky Way.
The latest discovery was made using the Sloan Digital Sky Survey, a projecting to map parts of the universe in three dimensions. The results will be published in the Astrophysical Journal. Another ring, known as the TriAnd Ring, may also be part of the Milky Way, further increasing its size. To verify their theory, astronomers will use data from Europe’s Gaia telescope, which is also mapping stars in the Milky Way.
The Milky Way (the New Scientist poster is magnified by clicking it) is thought contain more than 200 billion stars. This makes it a ‘middleweight’ galaxy with the largest galaxy known, IC 1101, containing more than 100 trillion stars. On a clear night, when you look up into the night sky the most you can see from any one point on the Earth is about 2,500 stars. Like more than two-thirds of the known galaxies, the Milky Way has a spiral shape. At the centre of the spiral, a lot of energy and, occasionally, vivid flares are created. Astronomers believe the Milky Way wasn’t always a stunning barred spiral. It formed into its current size by ‘eating’ other galaxies.
Credit: Mail Online (11 March 2015), New Scientist.