PSR B1620−26 is a
binary star
A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...
system located at a distance of 3,800
parsec
The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...
s (12,400
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) in the
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 ...
of
Messier 4
Messier 4 or M4 (also known as NGC 6121 or the Spider Globular Cluster) is a globular cluster in the constellation of Scorpius. It was discovered by Philippe Loys de Chéseaux in 1745 and catalogued by Charles Messier in 1764. It was the first g ...
(M4, NGC 6121) 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 ...
of
Scorpius
Scorpius is a zodiac constellation located in the Southern celestial hemisphere, where it sits near the center of the Milky Way, between Libra to the west and Sagittarius to the east. Scorpius is an ancient constellation whose recognition pred ...
.
The system is composed of a
pulsar
A pulsar (''pulsating star, on the model of quasar'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its Poles of astronomical bodies#Magnetic poles, magnetic poles. This radiation can be obse ...
(PSR B1620−26 A) and a
white dwarf
A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
star (WD B1620−26, or PSR B1620−26 B). As of 2000, the system is also confirmed to have an
exoplanet
An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...
orbiting the two stars.
History
The double system (''triple'' including the substellar companion) is just outside the core of the globular cluster. The age of the cluster has been estimated to be about 12.2 billion years.
Hence this is the age estimate for the birth of the planet, and two stars.
There is a minor dispute about the proper nomenclature rules to use for this unusual star system. One side regards the A/B convention of naming binary stars as having priority, so that the pulsar is PSR B1620−26 A, the white dwarf companion is PSR B1620−26 B and the planet is
PSR B1620−26 c
PSR may refer to:
Organizations
* Pacific School of Religion, Berkeley, California, US
* Palestinian Center for Policy and Survey Research
* Payment Systems Regulator in the United Kingdom
* Physicians for Social Responsibility, US
Political pa ...
. The other side considers PSR to apply only to stars which are pulsars, not their companions, so the white dwarf should be named using the WD convention, making the pulsar PSR B1620−26, the white dwarf "WD J1623−266", and the planet "PSR B1620−26 b." Early articles used the first convention, but star catalogs have been using the second.
The most recent proposal
provides a nomenclature like PSR B1620−26 (AB)b, including capital letters A and B in parentheses to identify inner stellar components of binary system, followed by italic letter b referred to outer planetary companion. In practice, context makes it clear whether the pulsar, the white dwarf, the planet, or the system as a whole is being referred to.
White dwarf
The mass of the white dwarf is 0.34
solar mass
The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...
es and orbits at a period of 191 days with an inclination of 55° relative to its pulsar companion.
[
]
Its age is approximately years.
Planetary system
PSR B1620−26 b
PSR B1620-26 b is an exoplanet located approximately 12,400 light-years from Earth in the constellation of Scorpius. It bears the unofficial nicknames "Methuselah" and "the Genesis planet" (named after the Biblical character Methuselah, who, acco ...
was originally detected through the Doppler shifts its orbit induces on signals from the star it orbits (in this case, changes in the apparent pulsation period of the pulsar).
In the early 1990s, a group of astronomers led by Donald Backer, studying what they thought was a binary pulsar, determined that a third object was needed to explain the observed Doppler shifts. Within a few years, the gravitational effects of the planet on the orbit of the pulsar and white dwarf had been measured, giving an estimate of the mass of the third object that was too small for it to be a star. The conclusion that the third object was a planet was announced by
Stephen Thorsett
Stephen Erik Thorsett (born December 3, 1964) is an American academic and astronomer serving as the president of Willamette University. His research interests include radio pulsars and gamma-ray bursts. He is known for measurements of the masses o ...
and his collaborators in 1993.
See also
*
PSR B1257+12
PSR B1257+12, alternatively designated PSR J1300+1240, is a millisecond pulsar, from the Sun, in the constellation Virgo, rotating at about 161 times per second (faster than the blade of a blender). It is also named Lich, after a powerf ...
*
Delta Trianguli
Delta Trianguli, also named Deltoton, is a spectroscopic binary star system approximately away in the constellation of Triangulum. The primary star is a yellow dwarf, while the secondary star is thought to be an orange dwarf. It has a ...
*
Pulsar planet
Pulsar planets are planets that are orbiting pulsars. The first such planets to be discovered were around a millisecond pulsar in 1992 and were the first extrasolar planets to be confirmed as discovered. Pulsars are extremely precise clocks and ...
*
List of exoplanets discovered before 2000
This is a list of exoplanets discovered before 2000.
For exoplanets detected only by radial velocity, the mass value is actually a lower limit. (See Minimum mass for more information.)
While the existence of a substellar companion to Gamma Cephei ...
- PSR B1620-26 b
References
External links
SolStation: PSR B1620−26
Binary stars
Pulsars
White dwarfs
Scorpius
2
Planetary systems with one confirmed planet
{{DEFAULTSORT:PSR B1620-26