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HADAR

(Beta Centauri). Residents of the southern hemisphere see a grand parade as Crux (the Southern Cross) rises and is followed by the two luminaries of Centaurus, Hadar and Rigel Kentaurus, the pair more commonly known as Beta and Alpha Centauri. The two named appropriately in order of brightness, Hadar (bright first magnitude, 0.61) is the sky's 11th brightest star. Hadar is a proper name of unknown meaning, and has been paired with the name "Wezen," the two applied to the two bright stars in Centaurus as well as to stf unknown meaning, and has been paired with the name "Wezen," the two applied to the two bright stars in Centaurus as well as to stars in Columba, "Wezen" now commonly used for Delta Canis Majoris. Hadar, less often known as Agena (from the "knee" of the Centaur), is quite the magnificent star: rather, stars. Alpha Centauri is notably brighter than Hadar, but only because (ignoring Proxima) it is the closest star (really a pair of stars) to the Earth. At a distance of 525 light years, blue class B (B1) Hadar is 130 times farther away, and is bright because it is truly and very generously luminous, shining (accounting for the ultraviolet radiated from the 25,500 Kelvin surface) 112,000 times more brightly than the Sun. Hadar, however, is not one star, but two. Sophisticated observations that rely on the interference properties of light show that the single point of light actually consists of a pair of nearly identical stars each some 55,000 times more luminous than the Sun separated (from our perspective) by only 2.5 astronomical units. The temperature and luminosity show each to contain 15 solar masses. Spectra suggest a an orbital period of not quite a year, this and the masses rendering them an actual 3 astronomical units apart. Twin Hadar also has a fourth magnitude sibling 1.3 seconds of arc away that, because of the brightness difference, is difficult to see and study. A class B dwarf, Hadar- B is a grand star in its own right, a star of 5 solar masses 1500 times more luminous than the Sun; it only pales by comparison with Hadar (or the Hadars) proper. Hadar-B orbits the close pair at a minimum distance of 210 astronomical units, taking at least 600 years to make the trip. Conjure a hypothetical planet orbiting Hadar-B. For us to survive, it would have to be as far from the star as Pluto is from the Sun. From there, the distant twins (each 12 solar diameters across) would appear as tiny disks two minutes of arc across separated by half a degree (the angular diameter of the Moon), each shining as much energy on the mythical planet as the Sun does upon us. The twins of Hadar appear to at the edge of shutting down their internal hydrogen fusion (if they have not done so already), and are beginning to evolve and die. Now some 12 million years old, they will quickly expand to become red supergiants and will surely affect each other quite profoundly. Within the next million or so years at least one may explode as a grand supernova. If it were to go off where it is today (which it will not), it would shine in our sky with nearly the brightness of the full Moon. One of the twins is also a variable of the "Beta Cephei" type (whose greatest exponent is Mirzam), the star subtlety chattering away with multiple periods of less than a day. Finally, Hadar is an X-ray source with a 2 million Kelvin wind
ltiple periods of less than a day. Finally, Hadar is an X-ray source with a 2 million Kelvin wind