The Galactic Center is the rotational center of the Milky Way galaxy. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply A galaxy is a massive gravitationally bound system consisting of Stars an Interstellar medium of gas and dust, and Dark matter It is located about 7. 6 kiloparsecs (24,800 LY) away from the Earth,^[1] in the direction of the constellation Sagittarius, where the Milky Way appears brightest. History The first direct measurements of an object at interstellar distances were undertaken by German Astronomer Friedrich Wilhelm Bessel in 1838 A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 In common usage a constellation is a group of celestial bodies that are connected together in some arrangement typically stars to form a visible figure or picture There is a supermassive black hole at the Galactic Center of the Milky Way. A supermassive black hole is a Black hole with a Mass of an order of magnitude between 105 and 1 The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply ^[2]

The Galactic Center as seen by one of the 2MASS infrared telescopes.

Proof of existence and location

Because of cool interstellar dust along the line of sight, the Galactic Center cannot be studied at visible, ultraviolet or soft X-ray wavelengths. Interstellar cloud is the generic name given to an accumulation of gas plasma and dust in our and other galaxies. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays X-radiation (composed of X-rays) is a form of Electromagnetic radiation. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. The available information about the Galactic Center comes from observations at gamma ray, hard X-ray, infrared, sub-millimetre and radio wavelengths. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Radio waves are electromagnetic waves occurring on the Radio frequency portion of the Electromagnetic spectrum.

Coordinates of Galactic Center were first found by Harlow Shapley in his 1918 study of the distribution of the globular clusters. Harlow Shapley ( November 2 1885 &ndash October 20 1972) was an American Astronomer. A globular cluster is a spherical collection of Stars that orbits a galactic core as a Satellite. In the Equatorial coordinate system they are: RA 17h45m40. The equatorial coordinate system is probably the most widely used Celestial coordinate system, whose equatorial coordinates are Declination (\delta Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere 04s, Dec -29° 00' 28. In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either 1" (J2000 epoch). In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body.

The complex radio source Sagittarius A appears to be located almost exactly at the Galactic Center, and contains an intense compact radio source, Sagittarius A*, which coincides with a supermassive black hole at the center of our Galaxy. Sagittarius A (or Sgr A) is a complex radio source at the center of our Galaxy, the Milky Way. Sagittarius A* (pronounced "A-star" standard abbreviation Sgr A*) is a bright and very compact source of Radio emission at the center of A supermassive black hole is a Black hole with a Mass of an order of magnitude between 105 and 1 Accretion of gas onto the black hole, probably involving a disk around it, would release energy to power the radio source, itself much larger than the black hole. A black hole is a theoretical region of space in which the Gravitational field is so powerful that nothing not even Electromagnetic radiation (e An accretion disc (or accretion disk) is a structure (often a Circumstellar disk) formed by diffuse material in orbital motion around a central body The latter is too small to see with present instruments.

Stellar population

The central parsec around Sagittarius A* contains thousands of stars. History The first direct measurements of an object at interstellar distances were undertaken by German Astronomer Friedrich Wilhelm Bessel in 1838 A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth Although most of them are old red main sequence stars, the Galactic Center is also rich in massive stars. The main sequence is the name for a continuous and distinctive band of stars that appear on a plot of stellar color versus brightness A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth More than 100 OB and Wolf-Rayet stars have been identified there so far. OB stars are hot massive Stars of spectral types O or B which form in loosely organized groups called OB associations They are short lived and They seem to have all been formed in a single star formation event a few million years ago. Star Formation is the process by which dense parts of Molecular clouds collapse into a ball of plasma to form a Star. The existence of these relatively young (though evolved) stars there was of a surprise to experts, who would have expected the tidal forces from the central black-hole to prevent their formation. The tidal force is a secondary effect of the Force of Gravity and is responsible for the Tides It arises because the gravitational acceleration experienced This paradox of youth is even more remarkable for stars that are on very tight orbits around Sagittarius A*, such as S2. S2 (also known as S0—2 is a star that is located close to the radio source Sagittarius A*, orbiting it with an orbital period of 15 The scenarios invoked to explain this formation involve either star formation in a massive star cluster offset from the Galactic Center that would have migrated to its current location once formed, or star formation within a massive, compact gas accretion disk around the central black-hole. Star clusters are groups of Stars which are gravitationally bound An accretion disc (or accretion disk) is a structure (often a Circumstellar disk) formed by diffuse material in orbital motion around a central body It is interesting to note that most of these 100 young, massive stars seem to be concentrated within one (according to the UCLA group) or two (according to the MPE group) disks, rather than randomly distributed within the central parsec. This observation however does not allow definite conclusions to be drawn at this point.

Star formation does not seem to be occurring currently at the Galactic center, although the Circumnuclear Disk of molecular gas that orbits the Galactic center at two parsecs seems a fairly favorable site for star formation. Work presented in 2002 by Antony Stark and Chris Martin mapping the gas density in a 400 light year region around the galactic center has revealed an accumulating ring with a mass several million times that of the Sun and near the critical density for star formation. A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by The Sun (Sol is the Star at the center of the Solar System. Star Formation is the process by which dense parts of Molecular clouds collapse into a ball of plasma to form a Star. They predict that in approximately 200 million years there will be an episode of starburst in the galactic center, with many stars forming rapidly and undergoing supernovae at a hundred times the current rate. The starburst may also be accompanied by the formation of galactic jets as matter falls into the central black hole. The lower-energy non-relativistic version of this phenomenon is described at Polar jet. A black hole is a theoretical region of space in which the Gravitational field is so powerful that nothing not even Electromagnetic radiation (e It is thought that the Milky Way undergoes a starburst of this sort every 500 million years.

See also

• Galactic anticenter
• Galactic coordinate system
• Sagittarius B2

Further reading

• Melia, Fulvio, The Black Hole in the Center of Our Galaxy, Princeton U Press, 2003
• Eckart, A. The Galactic anticenter is the point in the sky that lies in the direction opposite the center of the Milky Way galaxy. The galactic coordinate system is a Celestial coordinate system which is centered on the Sun and is aligned with the apparent center of the Milky Way galaxy Sagittarius B2 (Sgr B2 is a giant Molecular cloud of gas and dust that is located about 120 Parsecs from the center of the Milky Way. Fulvio Melia (born 2 August 1956) is an Italian - American Physicist / Astrophysicist and Author. , Schödel, R. , Straubmeier, C. , The Black Hole at the Center of the Milky Way, Imperial College Press, London, 2005
• Melia, Fulvio, The Galactic Supermassive Black Hole, Princeton U Press, 2007

References

External links

• UCLA Galactic Center Group
• Max Planck Institute for Extraterrestrial Physics Galactic Center Group
• The Galactic Supermassive Black Hole
• The Black Hole at the Center of the Milky Way
• The dark heart of the Milky Way
• Dramatic Increase in Supernova Explosions Looms
• APOD:
  • Journey to the Center of the Galaxy
  • A Galactic Cloud of Antimatter
  • Fast Stars Near the Galactic Center
  • At the Center of the Milky Way
  • Galactic Centre Starscape