Messier 2 or M2 (also designated NGC 7089) is a

globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Aquarius, five degrees north of the

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

Beta Aquarii Beta Aquarii is a single yellow supergiant star in the constellation of Aquarius. It has the official name Sadalsuud () and the Bayer designation β Aquarii, abbreviated Beta Aqr or β Aqr. Based upon parallax measurements obtained duri ...

. It was discovered by Jean-Dominique Maraldi in 1746, and is one of the largest known globular clusters.

Discovery and Visibility

M2 was discovered by the French astronomer Jean-Dominique Maraldi in 1746 while observing a comet with

Jacques Cassini Jacques Cassini (18 February 1677 – 16 April 1756) was a French astronomer, son of the famous Italian astronomer Giovanni Domenico Cassini. He was known as Cassini II. Biography Cassini was born at the Paris Observatory. He was first admitted ...

Charles Messier Charles Messier (; 26 June 1730 – 12 April 1817) was a French astronomer. He published an astronomical catalogue consisting of 110 nebulae and star clusters, which came to be known as the ''Messier objects'', referred to with th ...

rediscovered it in 1760, but thought that it is a

nebula A nebula (; or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral, or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regions, such as in the Pillars of Creation in ...

without any stars associated with it.

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

, in 1783, was the first to resolve individual stars in the cluster. M2 is, under extremely good conditions, just visible to the naked eye.

Binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...

or a

small telescope A small telescope is generally considered by professional astronomers to be any reflecting telescope with a primary mirror that is less than in diameter. By amateur standards, a small telescope can have a primary mirror/aperture less than in dia ...

will identify this cluster as non-stellar, while larger telescopes will resolve individual stars, of which the brightest are of

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

6.5.

Characteristics

M2 is about 55,000

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s distant from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. At 175 light-years in diameter, it is one of the larger globular clusters known. The cluster is rich, compact, and significantly elliptical. It is 12.5 billion years old and one of the older globular clusters associated with the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

galaxy. M2 contains about 150,000 stars, including 21 known

variable stars A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

. Its brightest stars are

red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–750 nanometres. It is a primary color in the RGB color model and a seconda ...

and

yellow giant A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzspru ...

stars. The overall

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

is F4. M2 is part of the

Gaia Sausage The Gaia Sausage or Gaia Enceladus is the remains of a dwarf galaxy (known as the Sausage Galaxy, Gaia-Enceladus-Sausage, or Gaia-Sausage-Enceladus) that merged with the Milky Way about 8–11 billion years ago. At least eight globular cluste ...

, the hypothesized remains of a merged dwarf galaxy. Data from ''

Gaia In Greek mythology, Gaia (; , a poetic form of ('), meaning 'land' or 'earth'),, , . also spelled Gaea (), is the personification of Earth. Gaia is the ancestral mother—sometimes parthenogenic—of all life. She is the mother of Uranus (S ...

'' has led to the discovery of an extended tidal

stellar stream In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as ...

, about 45 degrees long and 300 light-years (100 pc) wide, that is likely associated with M2. It was possibly perturbed due to the presence of the

Large Magellanic Cloud The Large Magellanic Cloud (LMC) is a dwarf galaxy and satellite galaxy of the Milky Way. At a distance of around , the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal Galaxy, Sagittarius Dwarf ...

. Messier 2 is located within our Milky Way galaxy, and is one of the oldest clusters of stars designated to the Milky Way. Like most globular clusters, M2 is found within the

galactic halo A galactic halo is an extended, roughly spherical component of a galaxy which extends beyond the main, visible component. Several distinct components of a galaxy comprise its halo: * the stellar halo * the galactic corona (hot gas, i.e. a plas ...

, specifically in the southern galactic cap. This places it right below the southern pole of the Milky Way.

Oosterhoff Classification

M2 is defined as an Oosterhoff type II globular cluster. Oosterhoff type is a classification system of globular clusters originally observed by

Pieter Oosterhoff Pieter Theodorus Oosterhoff (30 March 1904, Leeuwarden - 14 March 1978, Leiden) was a Dutch astronomer. He was the co-administrator, along with Jan Oort, of the Leiden Observatory in the Netherlands. His published papers are primarily in regard ...

in where globular clusters are generally separated into two types. Oosterhoff type is determined by

metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

, age, and average pulsation period of type ab RR Lyrae variable stars of the cluster. A cluster metallicity below −1.6, an age above 13 billion years, and an average RRab Lyrae pulsation period around .64 days indicates a type II cluster. This .64 day value, coupled with a metallicity of −1.65, provides evidence that M2 follows the Oosterhoff Gap phenomena. This is an observed gap in the grouping of type I and type II clusters in the Milky Way on a metallicity vs average RRab pulsation period plot. M2 is a bit of an anomaly in reference to Oosterhoff type. While it satisfies the metallicity and RRab Lyrae pulsation period conditions, it actually has an age of 12.5 Gyr, well below the cutoff age of 13 Gyr normal for a Oosterhoff type II cluster. This is unexpected because age of a cluster is generally determined from metallicity. However, this abnormality is explained in an article by Marín-Franch.

References

External links

M2,SEDS Messier pages

M2, Galactic Globular Clusters Database page
* {{DEFAULTSORT:Messier 002 Globular clusters NGC objects

002 002, 0O2, O02, OO2, or 002 may refer to: Airports *0O2, Baker Airport *O02, Nervino Airport Astronomy *1996 OO2, the minor planet 7499 L'Aquila *1990 OO2, the asteroid 9175 Graun Fiction *002, fictional British 00 Agent *''002 Operazione Luna'' ...

Gaia-Enceladus Aquarius (constellation) 17460911

Discovery and Visibility

Characteristics

Oosterhoff Classification

References

See also

External links