Messier 15
Encyclopedia
Messier 15 or M15 is a globular cluster
in the constellation
Pegasus
. It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier
's catalogue of comet
-like objects in 1764. At an estimated 13.2 billion years old, it is one of the oldest known globular clusters.
s from Earth
, and 175 light years in diameter. It has an absolute magnitude
of -9.2, which translates to a total luminosity
of 360,000 times that of the Sun
. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. 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
s (112) and pulsar
s (8), including one double neutron star
system, M15 C. M15 also contains Pease 1
, the first planetary nebula
discovered within a globular cluster in 1928. Just three others have been found in globular clusters since then. http://www.seds.org/messier/more/m015_h2.html
+12.6. The cluster appears 18 arc minutes in size.
s Uhuru
and Chandra X-ray Observatory
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.
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...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Pegasus
Pegasus (constellation)
Pegasus is a constellation in the northern sky, named after the winged horse Pegasus in Greek mythology. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations.-Stars:...
. It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier
Charles Messier
Charles Messier was a French astronomer most notable for publishing an astronomical catalogue consisting of deep sky objects such as nebulae and star clusters that came to be known as the 110 "Messier objects"...
's catalogue of comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
-like objects in 1764. At an estimated 13.2 billion years old, it is one of the oldest known globular clusters.
Characteristics
M15 is about 33,600 light-yearLight-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, and 175 light years in diameter. It has an absolute magnitude
Absolute magnitude
Absolute magnitude is the measure of a celestial object's intrinsic brightness. it is also the apparent magnitude a star would have if it were 32.6 light years away from Earth...
of -9.2, which translates to a total luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
of 360,000 times that of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as 'core collapse
Core collapse
Core collapse can refer to:* The collapse of the stellar core of a massive star, such as the core collapse that produces a Type II supernova.* The dynamic process that leads to a concentration of stars at the core of a Globular cluster....
' 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
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
s (112) and pulsar
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
s (8), including one double neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
system, M15 C. M15 also contains Pease 1
Pease 1
Pease 1 is a planetary nebula located within the globular cluster M15 33,600 light years away in the constellation Pegasus. It was the first planetary nebula known to exist within a globular cluster when it was discovered in 1928, and just three more have been found since. At magnitude 15.5, it...
, the first planetary nebula
Planetary nebula
A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
discovered within a globular cluster in 1928. Just three others have been found in globular clusters since then. http://www.seds.org/messier/more/m015_h2.html
Amateur astronomy
At magnitude 6.2, M15 approaches naked eye 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 diameter) will start to reveal individual stars, the brightest of which are of magnitudeApparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
+12.6. The cluster appears 18 arc minutes in size.
X-ray sources
Earth-orbiting satelliteSatellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
s Uhuru
Uhuru
Uhuru may refer to:, a Lake Victoria ferry in East Africa*Uhuru , campaigns for and achievement of national independence in Africa especially in Kenya, Uganda and Tanzania*Uhuru Kenyatta , Kenyan politician...
and Chandra X-ray Observatory
Chandra X-ray Observatory
The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
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.