Terzan 5
Encyclopedia
Terzan 5 is a heavily obscured globular cluster
belonging to the bulge
(the central star concentration) of the Milky Way
galaxy. It was one of six globulars discovered by French astronomer Agop Terzan
in 1968 and was initially labeled Terzan 11. The cluster was cataloged by the Two-Micron Sky Survey
as IRC–20385. It is situated in the Sagittarius constellation in the direction of the Milky Way
's center. Terzan 5 probably follows an unknown complicated orbit around the center of the galaxy, but currently it moves towards the Sun with the speed of around 90 km/s.
The absolute magnitude
of Terzan 5 is at least , meaning that its luminosity is about 100,000 times more than that of the Sun, and is close to the average absolute magnitude for galactic globular clusters. The small core of Terzan 5 has one of the highest star densities in the galaxy. Its volume mass density exceeds , while its volume luminosity density exceeds , where M☉ and L☉ are the Sun's mass and luminosity, respectively. The cluster also has one of the highest metallicities
among Milky Way's globular clusters—[Fe/H] =−0.21.
In 2009 it was discovered that Terzan 5 consists of at least two generations of stars with ages of 12 and 6 billion years and slightly different metallicities, possibly indicating that it is the core of a disrupted dwarf galaxy
, not a true globular cluster. There are only a few other globular clusters in Milky Way that contain stars with different ages. Among them are M54
and Omega Centauri
, the former being the core of Sagittarius Dwarf Elliptical Galaxy
. The cluster also contains around 1300 core helium
burning horizontal branch
(HB) stars, including at least one RR Lyrae variable
star.
s. The first such object, PSR B1744-24A, discovered in 1990, has the period of 11.56 ms
. The population of pulsars inside Terzan 5 includes PSR J1748–2446ad, the fastest known millisecond pulsar, which is spinning at 716 Hz (the rotation period is 1.40 ms).
Terzan 5 also contains an X-ray burster
, discovered in 1980, known as Terzan 5 or XB 1745-25. It also contains around 50 weaker X-ray sources, many of which are likely Low-mass X-ray binaries (LXMB) or cataclysmic variables.
The large number of X-ray source
s and millisecond pulsars may be a direct consequence of the high density of the cluster's core, which leads to a high rate of star collisions, and to formation of close binaries, including binary systems which contain a neutron star
.
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...
belonging to the bulge
Bulge (astronomy)
In astronomy, a bulge is a tightly packed group of stars within a larger formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies...
(the central star concentration) of 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...
galaxy. It was one of six globulars discovered by French astronomer Agop Terzan
Agop Terzan
Agop Terzan is a French–Armenian astronomer. Born in Istanbul, he received his BA in Mathematical and Astronomical Science in 1945. He received a Master's degree in Astronomy in 1949, and a PhD from Lyon University in 1965....
in 1968 and was initially labeled Terzan 11. The cluster was cataloged by the Two-Micron Sky Survey
Two-Micron Sky Survey
Two-Micron Sky Survey, or IRc, or Infrared compact, or Caltech infrared catalog is the astronomical catalogue of the infrared sources published in the 1969 by Neugebauer and Leighton....
as IRC–20385. It is situated in the Sagittarius constellation in the direction of 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...
's center. Terzan 5 probably follows an unknown complicated orbit around the center of the galaxy, but currently it moves towards the Sun with the speed of around 90 km/s.
The 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 Terzan 5 is at least , meaning that its luminosity is about 100,000 times more than that of the Sun, and is close to the average absolute magnitude for galactic globular clusters. The small core of Terzan 5 has one of the highest star densities in the galaxy. Its volume mass density exceeds , while its volume luminosity density exceeds , where M☉ and L☉ are the Sun's mass and luminosity, respectively. The cluster also has one of the highest metallicities
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
among Milky Way's globular clusters—
In 2009 it was discovered that Terzan 5 consists of at least two generations of stars with ages of 12 and 6 billion years and slightly different metallicities, possibly indicating that it is the core of a disrupted dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...
, not a true globular cluster. There are only a few other globular clusters in Milky Way that contain stars with different ages. Among them are M54
Messier 54
Messier 54 is a globular cluster in the constellation Sagittarius. It was discovered by Charles Messier in 1778 and subsequently included in his catalog of comet-like objects....
and Omega Centauri
Omega Centauri
Omega Centauri or NGC 5139 is a globular clusterin the constellation of Centaurus, discovered by Edmond Halley in 1677 who listed it as a nebula. Omega Centauri had been listed in Ptolemy's catalog 2000 years ago as a star. Lacaille included it in his catalog as number I.5...
, the former being the core of 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...
. The cluster also contains around 1300 core helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
burning horizontal branch
Horizontal branch
The horizontal branch is a stage of stellar evolution which immediately follows the red giant branch in stars whose masses are similar to the Sun's...
(HB) stars, including at least one RR Lyrae variable
RR Lyrae variable
RR Lyrae variables are periodic variable stars, commonly found in globular clusters, and often used as standard candles to measure galactic distances.This type of variable is named after the prototype, the variable star RR Lyrae in the constellation Lyra....
star.
Pulsars and X-ray sources
Terzan 5 is known to contain at least 25 millisecond radio pulsarMillisecond pulsar
A millisecond pulsar is a pulsar with a rotational period in the range of about 1-10 milliseconds. Millisecond pulsars have been detected in the radio, X-ray, and gamma ray portions of the electromagnetic spectrum. The origin of millisecond pulsars is still unknown...
s. The first such object, PSR B1744-24A, discovered in 1990, has the period of 11.56 ms
Millisecond
A millisecond is a thousandth of a second.10 milliseconds are called a centisecond....
. The population of pulsars inside Terzan 5 includes PSR J1748–2446ad, the fastest known millisecond pulsar, which is spinning at 716 Hz (the rotation period is 1.40 ms).
Terzan 5 also contains an X-ray burster
X-ray burster
X-ray bursters are one class of X-ray binary stars exhibiting periodic and rapid increases in luminosity peaked in the X-ray regime of the electromagnetic spectrum...
, discovered in 1980, known as Terzan 5 or XB 1745-25. It also contains around 50 weaker X-ray sources, many of which are likely Low-mass X-ray binaries (LXMB) or cataclysmic variables.
The large number of X-ray source
Astrophysical X-ray source
Astrophysical X-ray sources are astronomical objects with physical properties which result in the emission of X-rays.There are a number of types of astrophysical objects which emit X-rays, from galaxy clusters, through black holes in active galactic nuclei to galactic objects such as supernova...
s and millisecond pulsars may be a direct consequence of the high density of the cluster's core, which leads to a high rate of star collisions, and to formation of close binaries, including binary systems which contain a 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...
.