Eta Carinae: The Strange Case Of A Star That Refused To Die


Dazzling in its fierce, fiery brilliance, Eta Carinae is a stellar system composed of at least two stars sporting a combined luminosity that is greater than five million suns. The primary star inhabiting this system is also extremely unstable and probably doomed to go supernova sometime in the foreseeable future. However, this bright system of stars is a trickster. In fact, the Eta Carinae primary star should have died long ago, but didn’t. Almost 170 years ago, this glaring stellar behemoth experienced an enormous outburst that liberated almost as much energy as a typical supernova blast, that heralds the demise of a massive star. Yet that powerful eruption wasn’t enough to send that enormous star screaming into eternity, and astronomers have been hunting for clues to explain this enormous outburst ever since.

While there is no way to travel back in time to the mid-1800s, and observe first hand the giant eruption in all of its original glory, astronomers can now enjoy a fiery encore performance of that dramatic stellar blast. This rebroadcast comes courtesy of some wayward light streaming out from the explosion. Instead of traveling straight to our planet, some of the emitted light from the outburst rebounded–or “echoed”–off of interstellar dust, and is now first arriving at Earth. The term for this phenomenon is a light echo.

This “time machine”, that Mother Nature has generously provided, is based on the lucky fact that light travels at a finite speed through space–and instead of zipping straight to our planet, some the light streaming from the outburst apparently took a detour. The wayward light rebounded, and this light echo is behaving like a love letter written 170 years ago that is only now first arriving at its destination.

A Mysterious Star

Eta Carinae is situated approximately 7,500 light-years from Earth in the constellation Carina, which makes it a relatively nearby star. Nevertheless, there is no definite evidence showing that Eta Carinae was observed before the 17th century. However, the German navigator, Pieter Keyser (1540-1596) did describe seeing a fourth-magnitude star that well may have been Eta Carinae. The star that Pieter Keyser observed around 1595-1596, was at the correct position for it to have been this mysterious star. In turn, Keyser’s observations were copied onto the celestial globes of the Dutch-Flemish astronomer Petras Plancius (1552-1622) and the French engraver and cartographer Jodocus Hondius (1563-1612), as well as the 1603 Uranometricia of the German lawyer and astronomer Johann Bayer (1572-1625). The Dutch explorer Frederick de Houtman’s (1571-1627) independent star catalogue, also produced in 1603, does not include Eta Carinae among the other 4th magnitude stars located in that region.

The first known reliable observation was produced by the English astronomer Edmond Halley (1656-1742) in 1677, when he recorded the star dismissively as Sequens–meaning “following” relative to another star within a newly discovered constellation then dubbed Robur Carolinum. Halley’s Catalogus Stellarum Australium was published in 1679. The mysterious star was also recognized and named Eta Roboris Caroli, Eta Argus, or Eta Navis. Eta was observed in what was later to be known as the constellation Carina. However, it was not generally known as Eta Carinae until 1879, when the stars of Argo Navis were finally designated as the daughter constellations situated in the Uranometria Argentina of the American astronomer Benjamin Apthorp Gould (1824-1896).

Halley determined an approximate apparent magnitude for Eta Carinae of “4” at the time of his discovery, which was later calculated to be magnitude 3.3 on the scale used by astronomers today. Several possible earlier observations indicate that Eta Carinae did not grow much brighter than this for most of the 17th century. 바카라사이트

However, Eta Carinae brightened in 1837 from a 4th magnitude star to become brighter than the star Rigel. This proved to be the beginning of what is called its Great Eruption. Indeed, Eta Carinae became the second-brightest star in the sky between March 11 and March 14 1843. After 1856, it began to fade well below what the unaided human eye is able to see. A smaller eruption followed soon thereafter, when Eta Carinae reached 6th magnitude in 1892, before growing dim again. Since 1940, it has brightened consistently, growing brighter than magnitude 4.5 by 2014.

The blue-white star Rigel (Beta Orionis) is usually the 7th brightest star suspended in the dark night sky above our planet, as well as the brightest star in the Orion Constellation. However, it is occasionally out-dazzled within its constellation by the variable star Betelgeuse.

The duo of main stars within the Eta Carinae system display an eccentric orbit with a period of 5.54 years. The primary star is a true “oddball”, similar to a luminous blue variable, that started out at a hefty 150-250 solar-masses. However, the primary has shed at least 30 solar-masses already, and it is expected to go supernova in the near future. The behemoth star has the distinction of being the only one of its gigantic searing-hot kind known to produce ultraviolet laser emission. The secondary star of the fiery duo is extremely luminous–and very hot. This star is probably of spectral class O, and it weighs-in at an impressive 30 to 80 times solar-mass. The system is heavily blanketed by the Homunculus Nebula, which is composed of material hurled out from the primary during the Great Eruption. It is a dazzling denizen of the Trumpfer 16 open stellar cluster situated within the considerably larger Carina Nebula.

 


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