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plxzb4bljxuptdmu37y6This strange object which resembles a bottle gourd is actually a depiction of the largest yellow star known to science. HR5171A is located 11,700 light years from Earth in the heart of Centaurus (a southern constellation).  Actually the image above is two stars: HR5171A is part of a binary system and its companion star is so close that the topology of the hypergiant is affected. The smaller companion is not visible.  To quote Universe Today, “what we see is not the companion itself, but the regions gravitationally controlled and filled by the wind from the hypergiant.” It is uncanny how the giant star looks like a 1930s cartoon character’s head!  The combined system has a total mass 39 times that of our own sun, but their volume is vastly larger—nearly 1,300 times greater that that of the sun (and the luminosity of the star is a million times greater).  Although HR5171A is much less large than the true giants (like the astonishing Eta Carinae which has 120 solar masses), its ultimate fate is still not happy.  Yellow hypergiant stars are passing through a transitional phase on the way to going supernova (so enjoy it now, while you can).


Eta Carinae is a star system 8,000 light years from the solar system.  It contains a luminous blue hypergiant star which probably has about 100 times the mass of the sun and shines 4 million times more brightly.  For those of you keeping tally, that gives the star approximately the same mass as 33 million earths!

Eta Carinae was originally cataloged by Edmond Halley in 1677 (hence its stylish Latin name) as a comparatively dim 4th magnitude star, however astronomers noticed that its brightness varied greatly over the decades.  In 1827 it began to become significantly more luminous and by 1843 it was the second brightest star in the night sky (after Sirius, our next door stellar neighbor which is only 8.6 light years away).  The star then dimmed down to the eighth magnitude—becoming invisible to the naked eye.  Today it is believed that this strange occurrence was a supernova impostor event in which the star nearly exploded.  Looking at Eta Carinae now through the Hubble telescope reveals two huge hemispheres of material ejected from the star.   Scientists have named this cloud the Homunculus nebula and it is nearly a light year in diameter.

Eta Carinae and the Homunculus Nebula as photographed by the Hubble Space Telescope

Stars as massive as Eta Carinae are very rare.  At this stage of galactic development there are perhaps a dozen in a galaxy the size of the Milky Way (which contains 200 billion to 400 billion stars).  Eta Carinae is probably fated to die in a hypernova explosion (an immense supernova event).  A similar impostor event to Eta Carinae’s 1843 flare-up was witnessed on SN 2006jc, a star within galaxy UGC 4904 (perhaps you now appreciate the Latin and Arabic names of familiar nearby astronomical objects).  SN 2006jc went hypernova two years after its impostor nova event.  It is very possible that Eta Carinae no longer exists but was destroyed a long time ago.  The light we see now is eight thousand years old.  Who knows what happened since then?

When Eta Carinae goes hypernova it will destroy star systems nearby.  Additionally,  a massive gamma ray burst will shoot from both of its poles as its center collapses into a black hole. Any living, earth-like world caught in such a beam would be sterilized completely–although we are mercifully not currently in Eta Carinae’s polar vector…

Eta Carinae’s Fate? A Hypothetical Illustration of a Hypernova Event with Gamma Ray Burst (Credit: Nicolle Rager Fuller/NSF)

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January 2023