Monoceros Ring
Encyclopedia
The Monoceros
Ring is a ring of star
s around the Milky Way
which is proposed to consist of a stellar stream
torn from the Canis Major Dwarf Galaxy
as it merges with the Milky Way over the course of billions of years. It is a complex ringlike structure which wraps around our galaxy
three times, formed from the long filament of stars pulled from the Canis Major Dwarf Galaxy by tidal
forces as it orbits the Milky Way. The ring has a mass of 100 million solar masses and is 200,000 light years long.
The stream of stars was first reported in 2002 by astronomers conducting the Sloan Digital Sky Survey
. It was in the course of investigating this ring of stars, and a closely spaced group of globular cluster
s similar to those associated with the Sagittarius Dwarf Elliptical Galaxy
, that the Canis Major Dwarf Galaxy was discovered. In 2006, a study using 2MASS
data cast doubts on the nature of the "Ring", arguing that the data is suggestive of the fact that the ring is actually part of the warped galactic disc of the Milky Way. However, observations using the Anglo-Australian Telescope
published in 2007 suggest that a warped disc cannot create the observed structure, which must therefore be formed either by a flare of the Galactic disc or have an extra-Galactic origin.
Monoceros
Monoceros is a faint constellation on the celestial equator. Its name is Greek for unicorn. Its definition is attributed to the 17th-century Dutch cartographer Petrus Plancius. It is bordered by Orion to the west, Gemini to the north, Canis Major to the south and Hydra to the east...
Ring is a ring of star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s around the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
which is proposed to consist of a stellar stream
Stellar stream
This is a list of stellar streams. A stellar stream is an association of stars orbiting a galaxy that was once a globular cluster or dwarf galaxy that has now been torn apart and stretched out along its orbit by tidal forces...
torn from the Canis Major Dwarf Galaxy
Canis Major Dwarf Galaxy
The Canis Major Dwarf Galaxy is located in the same part of the sky as the constellation Canis Major. The galaxy contains a relatively high percentage of red giant stars, and is thought to contain an estimated one billion stars in all....
as it merges with the Milky Way over the course of billions of years. It is a complex ringlike structure which wraps around our galaxy
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
three times, formed from the long filament of stars pulled from the Canis Major Dwarf Galaxy by tidal
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
forces as it orbits the Milky Way. The ring has a mass of 100 million solar masses and is 200,000 light years long.
The stream of stars was first reported in 2002 by astronomers conducting the Sloan Digital Sky Survey
Sloan Digital Sky Survey
The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project was named after the Alfred P...
. It was in the course of investigating this ring of stars, and a closely spaced group of globular cluster
Globular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
s similar to those associated with the Sagittarius Dwarf Elliptical Galaxy
Sagittarius Dwarf Elliptical Galaxy
The Sagittarius Dwarf Elliptical Galaxy is an elliptical loop-shaped satellite galaxy of the Milky Way Galaxy. It consists of four globular clusters, the main cluster being discovered in 1994...
, that the Canis Major Dwarf Galaxy was discovered. In 2006, a study using 2MASS
2MASS
Observations for the Two Micron All-Sky Survey began in 1997 and were completed in 2001 at two telescopes located one each in the northern and southern hemispheres to ensure coverage of the entire sky...
data cast doubts on the nature of the "Ring", arguing that the data is suggestive of the fact that the ring is actually part of the warped galactic disc of the Milky Way. However, observations using the Anglo-Australian Telescope
Anglo-Australian Telescope
The Anglo-Australian Telescope is a 3.9 m equatorially mounted telescope operated by the Australian Astronomical Observatory and situated at the Siding Spring Observatory, Australia at an altitude of a little over 1100 m...
published in 2007 suggest that a warped disc cannot create the observed structure, which must therefore be formed either by a flare of the Galactic disc or have an extra-Galactic origin.
External links
- Monoceros Ring at Space Wiki
- The Ghost of Sagittarius and Lumps in the Halo of the Milky Way Newberg H. J., et al., 2002, ApJAstrophysical JournalThe Astrophysical Journal is a peer-reviewed scientific journal covering astronomy and astrophysics. It was founded in 1895 by the American astronomers George Ellery Hale and James Edward Keeler. It publishes three 500-page issues per month....
, 569, 245 - Deriving The Shape Of The Galactic Stellar Disc (SkyNightly) March 17, 2006
- Deriving the shape of the Galactic stellar disc, A&A press release, March 16, 2006
- Outer structure of the Galactic warp and flare: explaining the Canis Major over-density, Astronomy & Astrophysics, 2006
- The AAT/WFI survey of the Monoceros Ring and Canis Major Dwarf galaxy: I. from l = (193 - 276)°, Conn, Blair C., et al., 2007, MNRASMonthly Notices of the Royal Astronomical SocietyMonthly Notices of the Royal Astronomical Society is one of the world's leading scientific journals in astronomy and astrophysics. It has been in continuous existence since 1827 and publishes peer-reviewed letters and papers reporting original research in relevant fields...
, in press