科学家发现最冷恒星 表面温度像地球夏天

The temperature of the surface is like a hot summer's day in Arizona or Seville - and would be quite pleasant for humans. It's the coldest object ever photographed outside our solar system.

But WD 0806-661 B is not a planet - it's a very small star. Its mass is just six to nine times the gas giant Jupiter.

Penn State Associate Professor of Astronomy and Astrophysics Kevin Luhman, who discovered the object said, "It is a very small star with an atmospheric temperature about as cool as the Earth's."

The astronomers used Nasa's Spitzer space telescope - the most sensitive space telescope on Earth - to find the cold star, scanning 600 near-earth stars for objects orbiting them. Infrared telescopes are used because cold objects "shine out" brightly in the images. The record-breaking star is 63 million light years from Earth and orbits a dense, collapsed "white dwarf" star.

The star is a brown dwarf - and formed, like other stars, out of a cloud of dust and gas.

But because it failed to accumulate enough mass from the dust cloud, the thermonuclear reaction that "lights up" normal stars fail to ignite.

The new brown dwarf's surface is between 27 and 80 degrees centigrade - so in places, it's a temperature humans might enjoy.

Ever since brown dwarfs first were discovered in 1995, astronomers have been trying to find new record holders for the coldest brown dwarfs - the objects are seen as valuable laboratories to help us understand the atmospheres of extrasolar planets with Earth-like temperatures.

Astronomers have named the brown dwarf "WD 0806-661 B". It orbits the "white dwarf" core of a star . The white dwarf would have shone like our sun until its outer layers were expelled into space in the final stages of a star's life.

"The distance of this white dwarf from the Sun is 63 light-years, which is very near our solar system compared with most stars in our galaxy", Luhman said.

The orbit of the brown dwarf is huge, about 2,500 times the distance between Earth and the sun.

据英国《每日邮报》10月21日报道，这颗星球表面的温度就像是在亚利桑那州或是塞利维亚的夏天——非常宜人。这也是目前拍摄到的太阳系外温度最低的星体。

但是WD 0806-661 B号星球并不是一颗行星——而是一颗非常小的恒星。它的质量仅仅是巨大的气体行星木星的6-9倍。

美国宾夕法尼亚州立大学天文与天体物理学副教授凯文·卢迈发现了这一星体，他说：“这是一颗非常小的恒星，它的大气温度和地球的一样凉爽。”

科学家们利用美国宇航局斯皮策太空望远镜——世界上灵敏度最高的太空望远镜——来寻找较冷的恒星，通过环绕的天体扫描到了600颗恒星。运用红外望远镜是因为寒冷的星体在图像中会明亮地“闪耀”。这颗破纪录的恒星距离地球6300万光年，围绕着一颗高密度的白矮星运动。

这颗恒星是褐矮星——像其他恒星一样，外部由尘埃和气体云构成。

但是因为它没能通过尘埃云累积足够的质量，所以也没有激起“点亮”一般恒星的核聚变。

这颗新发现的褐矮星地表温度在27到80度之间——在这些地方，温度很适宜人类居住。

褐矮星第一次被发现是在1995年，天文学家一直在试图寻找最冷褐矮星的新纪录保持者——这一星体被视为是有价值的实验点，可以帮助我们了解太阳系外与地球温度类似的星球的大气状况。

天文学家将这颗“褐矮星”命名为“WD 0806-661 B”号。它环绕着一颗恒星的白矮星内核运动。这颗白矮星就像太阳照射地球一样照射这颗星球，直到它走到生命尽头，外层逐渐冷却。

“这颗白矮星距离太阳63光年，与银河系中大多数星球相比，它距离我们的太阳系非常近。”卢迈说。

这颗褐矮星的运行轨道相当庞大，大约是地球到太阳距离的2500倍。