Eta Carinae

Eta Carinae may be about to explode. But no one knows when - it may be next year, it may be one million years from now. Eta Carinae's mass - about 100 times greater than our Sun - makes it an excellent candidate for a full blown supernova. Historical records do show that about 150 years ago Eta Carinae underwent an unusual outburst that made it one of the brightest stars in the southern sky. Eta Carinae, in the Keyhole Nebula, is the only star currently thought to emit natural LASER light. This image, taken in 1996, resulted from sophisticated image-processing procedures designed to bring out new details in the unusual nebula that surrounds this rogue star. Now clearly visible are two distinct lobes, a hot central region, and strange radial streaks. The lobes are filled with lanes of gas and dust which absorb the blue and ultraviolet light emitted near the center. The streaks remain unexplained. (Text adapted from NASA.)

Eta Carinae可能即将爆炸。但没人知道具体时间——可能是一年后，也可能是一百万年后。Eta Carinae的质量——大约是太阳的100倍——使其成为一颗很可能爆发超新星的候选星。历史记录显示，大约150年前，Eta Carinae曾发生过异常的爆发，使其成为南天最亮的恒星之一。位于Keyhole星云中的Eta Carinae，是目前唯一被认为能够发出自然激光光的恒星。这张1996年拍摄的图像，是通过复杂的图像处理程序制作的，目的是突出星云中不寻常细节。现在可以清楚地看到两个明显的云团，一个炽热的中心区域，以及奇怪的径向条纹。云团中充满了气体和尘埃的通道，它们吸收了中心区域发出的蓝光和紫外光。这些条纹仍无法解释。（文本改编自NASA。）

"This star was first cataloged by Edmond Halley in 1677, as a star of fourth magnitude. Since, its brightness has varied in a most remarkable way: In 1730, its brightness reached mag 2, and again fell to mag 4 in about 1782. It brightened again about 1801 and faded back to 4th magnitude in 1811. In 1820, Eta began to brighten steadily, reaching 2nd magnitude in 1822 and 1st mag in 1827. After this first preliminary maximum, the star faded back to mag 2 for about 5 years, then rose again to about mag 0. After a further slight decline, Eta's brightness increased once more and reached its maximal brilliance of nearly -1.0 in April 1843, when it outshone all stars in the sky but Sirius. After this brilliant show, the star slowly faded continuously, and became invisible in 1868. Interrupted by two minor outbursts around 1870 and 1889, Eta Carinae faded to about 8th magnitude around 1900, where it remained until 1941. At that time, the star began to brighten again, and reached 7th magnitude about 1953. Slowly and steadily, Eta Carinae became brighter until about 6th magnitude in the early 1990s - the star reached naked-eye visibility again at that time. Then in 1998-99, the star suddenly brightened by about a factor two."(SEDS)

这颗星最早于1677年由埃德蒙·哈雷编入星表，列为四等星。此后，它的亮度变化异常显著：1730年，其亮度达到2等，随后又在约1782年降至4等。1801年，它再次变亮，1811年又降至4等。1820年，Eta开始稳步变亮，1822年达到2等，1827年达到1等。在第一次初步峰值之后，这颗星又暗淡下来，持续了大约5年，之后又回升到约0等。在进一步轻微下降后，Eta的亮度再次增加，并在1843年4月达到接近-1.0的峰值亮度，当时它比天空中所有其他恒星都更亮，甚至超过了天狼星。在这一辉煌时期之后，这颗星逐渐变暗，直至1868年消失。1870年和1889年之间曾有两次小爆发，Eta在1900年左右降至约8等，此后一直保持到1941年。此时，这颗星再次变亮，1953年达到7等。此后，Eta Carinae逐渐变亮，直到20世纪90年代初达到约6等，此时它再次变得肉眼可见。然后在1998-1999年，这颗星突然变亮了约两倍。

Eta Carinae is about 7500 light years from the Earth. NASA's Far Ultraviolet Spectroscopic Explorer detected a partner of Eta Carinae in 2005. The companion was detected by the eclipsing of Eta Carinae's X-rays with a period of 5.5 years.