太美了！

麒麟座V838

What caused this outburst of V838 Mon? For reasons unknown, star V838 Mon’s outer surface suddenly greatly expanded with the result that it became one of the brighter stars in the Milky Way Galaxy in early 2002. Then, just as suddenly, it shrunk and faded. A stellar flash like this had never been seen before — supernovas and novas expel matter out into space. Although the V838 Mon flash appears to expel material into space, what is seen in the featured image from the Hubble Space Telescope is actually an outwardly expanding light echo of the original flash. In a light echo, light from the flash is reflected by successively more distant surfaces in the complex array of ambient interstellar dust that already surrounded the star. V838 Mon lies about 20,000 light years away toward the constellation of the unicorn (Monoceros), while the light echo above spans about six light years in diameter.

是什么導(dǎo)致麒麟座V838星（V838 Mon）發(fā)生爆發(fā)？因某些未知的原因，麒麟座V838星的外層突然急遽擴(kuò)張，讓它在2002年初成為銀河系的亮星之一。然后，它的變暗就如變亮一樣突然快速。這種恒星亮閃前所未見(jiàn)。超新星或新星會(huì)把物質(zhì)拋入太空中，而乍看之下，麒麟座V838星的爆發(fā)也像是有物質(zhì)被拋入太空。不過(guò)，如這幅由哈伯太空望遠(yuǎn)鏡所拍攝的主題影像所示，實(shí)際向外傳播的只是亮閃外傳所造成的回光而已。所謂回光，是指亮閃從環(huán)拱恒星、距離漸增的數(shù)個(gè)星際塵埃殼層反射之現(xiàn)象。V838星位在南天的麒麟座內(nèi)，距離我們約20,000光年遠(yuǎn)，而上面影像的回光直徑約為6光年。