Hadar, also known as Beta Centauri, is the second-brightest object in the constellation of Centaurus. It is the 11th brightest star in the night sky though it is actually a triple star system.
Key Facts & Summary
- Beta Centauri has an apparent magnitude of 0.61, and an absolute magnitude of – 4.53, being around 390 light-years / 120 parsecs away from the Sun.
- The Beta Centauri star system is composed out of three stars. Two of them – Beta Centauri Aa and Ab are of the spectral class B1 III, while the third one, Beta Centauri B is of spectral type B1V.
- Beta Centauri Aa and Ab are blue giant stars that are evolving away from the main sequence. Both stars are also Beta Cephei Variable stars – thus they have multiple pulsations of just a few hours.
- Beta Centauri B has been determined to be a blue-white dwarf.
- Beta Centauri Aa is the biggest star out of the Centauri system. It has around 10.7 solar masses and a radius of around 13 times that of the sun.
- Beta Centauri Ab appears to be the second biggest star, with an estimated 10.3 solar masses, though its radius is unknown.
- Beta Centauri B has been estimated to have around 4.61 solar masses.
- All the stars in the Beta Centauri system appear to be several times bigger than our sun.
- Both Beta Centauri A and B appear to have similar surface temperatures. It has been estimated that they have around 2.500 K with a margin of minus or plus 2.000 K.
- The Beta Centauri system is estimated to be around 14.1 million years old. It is quite young, much younger than our sun.
- Both Beta Centauri Aa and Ab are expected to end their life in a supernova explosion. This is quite rare, few other stars have been discovered to be supernova candidates and also be in the same star system.
- Hadar/Beta Centaurus and Rigil Kent/Alpha Centaurus form the Southern Pointer Stars.
The traditional name of Beta Centauri was Hada and Agena. Both names are derived from the Arabic language. The root’s meaning is “to be present” or “on the ground” or “settled, civilized area.” It is believed to be named as such because the star appears near to the horizon as viewed from low altitudes.
The name Agena is believed to be derived from the Latin genua – which translates to knees. It has been named as such since the star seems to be located in the left knee of the celestial centaur depicted in the constellation Centaurus.
The Beta Centauri system is estimated to be around 14.1 million years old. It is quite young, much younger than our sun. Its origin is unknown, it may have formed from either a molecular cloud of dust and gas or a nebula. Gravity pulled the swirling gas and dust together to form the stars of the Beta Centauri System.
Distance, Size, and Mass
Hadar /Beta Centauri is around 390 light-years / 120 parsecs away from the Sun. It is located in the famous Centaurus constellation. The primary star, Beta Centauri Aa, is the biggest star out of the Centauri system.
It has around 10.7 solar masses and a radius of around 13 times that of the sun. This means that its diameter is around 16 times bigger than that of the suns.
The secondary star, Beta Centauri Ab appears to be the second biggest star, with an estimated 10.3 solar masses, though its radius is not yet certainly established. Both these stars are speculated to be at least 10 times bigger than our sun.
The third star, Beta Centauri B, is the smallest. It has been estimated to have around 4.61 solar masses.
The first two stars – Beta Centauri Aa and Ab are of the spectral class B1 III. The star system as a whole has an apparent magnitude of 0.61 and an absolute magnitude of -4.53.
Both Beta Centauri Aa and Ab are variable stars. They are classified as Beta Cephei variable stars. Since their luminosity is of class III, it indicates that both stars are evolving away from the main sequence.
Their brightness varies through multiple pulsation periods of just a few hours. The full range of variability has bot been identified, but it is no more than a few hundredths of a magnitude.
The Hadar/Beta Centauri system is around 41.700 times brighter than our sun. Beta Centauri Aa and Ab have been estimated to have surface temperatures of around 25.000 K, this means that both stars are 4.3 times hotter than our sun.
The third component, a white dwarf, is a B1 star with an apparent magnitude of 4. Its spectral type has been classified as a B1V.
The two blue giants, Beta Centaurus Aa and Ab, are 4 AU away from one another and orbit each other once every 357 days in a highly eccentric orbit. The third component, Beta Centauri B, is at around 100 AU away from the primary pair. Beta Centauri B orbits the primary pair once every 1.500 or so.
The stars forming the primary pair, Beta Centauri Aa and Ab, are very close to each other. Because of this, their system is considered a spectroscopic binary system.
The Hadar/Beta Centaurus star system is located in the constellation of Centaurus. It is the second-brightest object in the constellation after Alpha Centauri.
The Centaurus constellation is one of the Greek constellations and it is located in the southern hemisphere. It represents the centaur, the half-man, half-horse creature in Greek mythology.
The Centaurus constellation contains two of the top ten brightest stars in the night sky, one of the brightest galaxies in the night sky Centaurus A, the globular cluster Omega Centauri, the blue planetary nebula, and also the Boomerang Nebula is also located here.
Hadar/Beta Centaurus along with Alpha Centaurus, serve as pointers to the Southern Cross asterism, which lies under the centaur’s rear legs.
Both Beta Centaurus Aa and Ab are in their giant phases, and will most likely end their lives in a double supernova explosion. It is unlikely that both stars will explode at the same time, though it is clear that no matter what star goes off first, it will strongly affect the other, possibly even prompting the other’s supernova explosion.
Did you know?
- For the Chinese, Hadar was known as the First Star of the Horse’s Abdomen – referring to the celestial centaur.
- The Boorang people of northwestern Victoria in Australia knew Beta Centaurus and Alpha Centaurus as Bermbermgle – two brothers from folklore, who were known in ages past both for their daring, and their penchant for destroying things. They are commemorated for killing Tchingal – represented by the Coalsack Nebula.
- Even though Ptolemy catalogued the constellation of Centaurus in the 2nd century, the constellation was known by others before him such as the astronomer Eudoxus, and the poet Aratus.
- The Centaurus constellation contains 11 stars with confirmed exoplanets orbiting them. This constellation also doesn’t have any Messier objects.