Messier 15 or M15 (also designated NGC 7078) is a
globular cluster
A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of memb ...
in the
constellation Pegasus
Pegasus ( grc-gre, Πήγασος, Pḗgasos; la, Pegasus, Pegasos) is one of the best known creatures in Greek mythology. He is a winged divine stallion usually depicted as pure white in color. He was sired by Poseidon, in his role as hor ...
. It was discovered by
Jean-Dominique Maraldi
Giovanni Domenico () Maraldi (17 April 1709 – 14 November 1788) was an Italian-born astronomer, nephew of Giacomo F. Maraldi.
Born at Perinaldo, Liguria, Maraldi came to Paris in 1727 and became a member of the French Academy of Sciences in 173 ...
in 1746 and included in
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''. Messier's purpose f ...
's catalogue of
comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or Coma (cometary), coma, and sometimes also a Comet ta ...
-like objects in 1764. At an estimated 12.5±1.3 billion years old, it is one of the oldest known globular clusters.
Characteristics
M 15 is about 35,700
light-year
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 101 ...
s from
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...
,
[ and 175 light-years in diameter.] It has an absolute magnitude
Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it we ...
of −9.2, which translates to a total luminosity
Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a s ...
of 360,000 times that of the Sun. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy
The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked ey ...
. Its core has undergone a contraction known as " core collapse" and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole.[
]
Home to over 100,000 stars, the cluster is notable for containing a large number of variable star
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...
s (112) and pulsar
A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward E ...
s (8), including one double neutron star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...
system, M15-C. It also contains Pease 1, the first planetary nebula
A planetary nebula (PN, plural PNe) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives.
The term "planetary nebula" is a misnomer because they are unrelate ...
discovered within a globular cluster in 1928. Just three others have been found in globular clusters since then.
Amateur astronomy
At magnitude 6.2, M15 approaches naked eye
Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...
visibility under good conditions and can be observed with binoculars or a small telescope, appearing as a fuzzy star. Telescopes with a larger aperture (at least 6 in. (150 mm)) will start to reveal individual stars, the brightest of which are of magnitude +12.6. The cluster appears 18 arc minutes in size (three tenths of a degree across). M15 is 4.2° WNW of the brightest star of Pegasus, Epsilon Pegasi.
X-ray sources
Earth-orbiting satellites Uhuru
Uhuru (a Swahili word meaning ''freedom'') may refer to:
People
* Uhuru Hamiter (born 1973), American football player
* Uhuru Kenyatta (born 1961), President of Kenya since 2013
Places
*Uhuru (Tanzanian ward), an administrative ward in the Dodoma ...
and Chandra X-ray Observatory
The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources ...
have detected two bright X-ray sources in this cluster: Messier 15 X-1 (4U 2129+12) and Messier 15 X-2.[
][
] The former appears to be the first astronomical X-ray source detected in Pegasus.
Gallery
Image:M15 core lucky 10pc.gif, The central square arcminute of M15 imaged using the lucky imaging
Lucky imaging (also called lucky exposures) is one form of speckle imaging used for astrophotography. Speckle imaging techniques use a high-speed camera with exposure times short enough (100 ms or less) so that the changes in the Earth's atm ...
technique
Image:M15map.png, Map showing the location of M15
Image:New Hubble image of star cluster Messier 15.jpg, M15 photographed by HST. The planetary nebula
A planetary nebula (PN, plural PNe) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives.
The term "planetary nebula" is a misnomer because they are unrelate ...
Pease 1 can be seen as a small blue object to the upper left of the core of the cluster.
See also
* List of Messier objects
The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ''Catalogue des Nébuleuses et des Amas d'Étoiles'' (''Catalogue of Nebulae and Star Clusters'').
Because Messier was only in ...
* X-ray astronomy
References
External links
Messier 15, SEDS Messier pages
Messier 15, Galactic Globular Clusters Database page
Globular Cluster Photometry With the Hubble Space Telescope. V. WFPC Study of M15's Central density Cusp
Wikisky.org SDSS image of M15
*
*
{{Sky, 21, 29, 58.38, , 12, 10, 00.6, 33600
Messier 015
Messier 015
015
Fifteen or 15 may refer to:
*15 (number), the natural number following 14 and preceding 16
*one of the years 15 BC, AD 15, 1915, 2015
Music
*Fifteen (band), a punk rock band
Albums
* ''15'' (Buckcherry album), 2005
* ''15'' (Ani Lorak album ...
Messier 015
Astronomical X-ray sources
X-ray astronomy
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