科学家捕捉到特大黑洞内部拔河大战（图）

2009年04月08日 09:38  新浪科技

                               
登录/注册后可看大图

科学家发现黑洞靠与热辐射风拔河调节能量

新浪科技讯 北京时间4月8日消息，据美国太空网报道，科学家发现，通过与其“碎片盘”吹来的一股炽热辐射风上演拔河大战，相当于数十亿个太阳的特大质量黑洞能够调节自身能量。

   经过长达10年的观测，钱德拉X射线天文台最终发现了第一个有关发生于质量只相当于14个太阳的小黑洞内的这种神秘现象的明显证据。哈佛大学天体物理学家约瑟夫·尼尔逊(Joseph Nielson)表示：“特大质量黑洞附近存在数千颗恒星，可以‘摆布’整个星系的物质。也就是说，特大质量黑洞可能拥有更多自我调节机会。”
　　
怪异的“病态”天体
　　
黑洞拥有可怕的力量，一旦被其俘虏，任何物质——甚至于光线都无法逃离。但在黑洞周围，一系列活动产生的高能辐射——包括无线电波和X射线——却可以进入太空。有时候，这种能量“流失”显得非常杂乱，部分能量可导入聚焦喷射流，喷射流沿着黑洞的旋转轴朝两个方向射出。
　
　钱德拉X射线天文台一直对无法预知的黑洞GRS 1915+105进行观测，这颗黑洞拥有14种不同的亮度状态，其中包括一种“心跳”状态——亮度会周期性增大，如同心脏监视器描绘出的心电图。20多年来，这些未知状态让对GRS 1915+105系统的观测变得异常复杂，虽然每一个大型地面及太空观测台都曾一瞥这种现象。
　
　尼尔森在接受太空网(SPACE.com)采访时说：“由于这种怪异的光变曲线，黑洞被形象地称之为‘病态’天体。能够发现辐射风和喷射流的基本物理学原理，我们都感到非常兴奋。”在偶尔的能量喷射以及其它活动之后，绝大多数黑洞通常都拥有较长的“平静期”，但GRS 1915显然是个另类。这颗黑洞体积虽小，但却异常活跃，已经拥有长达17年的喷射史。
　
　与热辐射风上演拉锯战
　
　钱德拉X射线天文台观测结果显示，GRS 1915的能量喷射一直与热辐射风上演拉锯战，热辐射风来自黑洞周围尘埃与气体增长盘炙热的内部区域。尼尔逊说：“外部增长盘实际上吸收了部分能量，并且本质上开始蒸发。随着能量流出增长盘，它会吸收更多辐射和动量，直至辐射风的速度达到每秒1000公里以上。”与此同时，外部增长盘的蒸发作用则剥夺了黑洞的质量喷射流，并将其作为燃料，直至蒸发殆尽。但质量喷射流却会再次出现，其中的原因仍旧是一个不解之谜。
　
　相比之下，科学家更多地了解操纵热辐射风的可能机制，其中包括除与GRS 1915这个例子有关的热量驱动或X射线加热以外的因素。磁场也能够驱动小黑洞(也被称之为“微型类星体”)周围的辐射风。尼尔逊指出：“我们面临着一个新的谜团——为何一些微型类星体产生磁场驱动下的辐射风，而其它成员却产生热量驱动下的辐射风？迄今为止，我们还不知道这个问题的答案。”
　
　一个处于进行时的迷
　　
任何情况下，喷射流的维持时间都存在差异。尼尔逊说：“可能只有短短几分钟，也可能持续几天或者几周时间。有时候，喷射流和辐射风会全部停止，只有一个安静的增长盘慢慢给这个黑洞输送能量。”
　
　现在的GRS 1915继续提供有用信息，研究人员可利用这些信息了解其超大质量黑洞“兄弟”，与后者有关的观测将进行相当长时间。据悉，这个小黑洞发生的持续一小时的变化相当于一个超大质量黑洞长达一万年的变化，如果后者的质量是太阳的10亿倍。
　
　钱德拉X射线天文台的大部分观测数据只与这个小黑洞有关，研究人员的数据分析工作尚未结束。尼尔逊说：“这有点像回头去看每一块拼图上的图案，钱德拉非常胜任这份工作，为我们提供了大量宝贵数据。”(秋凌)

中国的媒体总是不给原始的出处，费了一番功夫，终于找到了给文的英文原文：

Black Holes Caught in Tug-of-War
By Jeremy Hsu
Staff Writer
posted: 06 April 2009
10:28 am ET

Supermassive black holes that pack the heft of billions of suns have the capacity to regulate their energy during a tug-of-war with a hot radiation wind that blows in from their debris disks.

Now 10 years worth of observations from the Chandra X-ray Observatory have uncovered the first clear evidence of this mysterious phenomenon occurring in a small black hole just 14 times the mass of the sun.

"The supermassive black hole has thousands of stars nearby, a whole galaxy of matter to push around," said Joseph Nielson, an astrophysicist at the Harvard University. "So it's more like supermassive black holes have more opportunity to self-regulate."

The difficult patient
Black holes are so powerful that matter and even light cannot get out once trapped. But around black holes, a flurry of activity creates high-energy radiation — including radio waves and X-rays — that does flow out into space. Sometimes it all gets pretty messy, and some of the energy can be channeled into focused jets that shoot out in both direction along the axis of the black hole's rotation.

Chandra has kept an eye on a notoriously unpredictable black hole that has 14 states of varying brightness, including a "heartbeat" state where periodic spikes in brightness resemble an EKG reading on a heart monitor.

Those unknown fluttering states have complicated observations of the GRS 1915+105 system for more than two decades, even though every major ground and space observatory has taken a peek at one time or another.

"These light curves are so bizarre that the black hole has been described as 'pathological,'" Nielson told SPACE.com "So the fact that we can see past all that, to the fundamental physics of winds and jets, is very exciting."

Most black holes ordinarily have long periods of quiet followed by occasional outbursts of jets and other activity, and so GRS 1915 is not unusual in that respect. But the small and feisty black hole does stand out by having had active outbursts for 17 years.

On and off again
The black hole's energy jet continually fights a seesaw battle with the hot radiation wind, as revealed in Chandra's X-ray observations. That wind flows in from the hot inner regions of the dusty, gaseous accretion disk surrounding the black hole.

"The outer disk actually absorbs some of that energy, and essentially begins to evaporate," Nielson said. "As it flows away from the disk, it absorbs even more of that radiation and its momentum, until the wind attains speeds of 1000 km/s [621 mi/s] or more."

Evaporation of the outer disk deprives the black hole jet of the mass that serves as its fuel, and eventually chokes it off. But the jets start up again. How the jets start up again remains a mystery.

Scientists know more about possible mechanisms driving the hot wind, which can include factors beyond the thermal driving or X-ray heating in the case of GRS 1915. Magnetic fields can also drive such winds around small black holes, also known as micro-quasars.

"So our paper kind of raises a new mystery: why do some micro-quasars produce magnetically-driven winds and others produce thermally-driven winds?" Nielson noted. "Right now, we just don't know the answer."

An ongoing enigma
In any case, the jet appearances can also differ greatly in terms of how long they keep going.

"Maybe it's just for a few hours, but it could be for days or weeks," Nielson noted. "And some day, it will stop altogether -- no jets, no winds, just a quiet accretion disk slowly feeding the black hole."

But for now, GRS 1915 continues to provide useful information that researchers can apply to understanding its super-massive black hole cousins, which can defy observation for timescale reasons. An hour-long change in the small black hole would be equivalent to a timescale of 10,000 years in a super-massive black hole, if the latter weighed a billion times the mass of the sun.

Much more Chandra data also remains for just this one black hole, and researchers have yet to analyze it all.

"It's sort of like going back to see what's on each puzzle piece," Nielson said. "Chandra is great for this sort of thing, and we've got lots of data to pore over."
引自：http://www.space.com/scienceastronomy/090406-mm-black-hole.html

此文中，完全没有说什么“黑洞内部”。根据现有理论，黑洞内部是完全不可见的，此文译者的水平，差强人意。

我貌似翻译过江涛发的文章。我个人看法是黑洞附近的吸积盘会周期性的产生一种旋风一样的东西，并把吸积盘吹掉一部分。此时，黑洞的喷流就会停止。这就是黑洞的自我调节功能。很显然，黑洞喷流的燃料就是吸积盘，与新浪所翻译的完全相反。

ls已经升华到哲学高度了

真是有趣啊！