主题：【科普知识】黑洞原来在唱歌 -- 杨不过

Black Holes Sing Bass, But Humans Can't Hear Them

Tue September 9, 2003 01:55 PM ET

By Deborah Zabarenko

WASHINGTON (Reuters) - Big black holes sing bass.

One particularly monstrous black hole has probably been humming B flat for billions of years, but at a pitch no human could hear, let alone sing, astronomers said on Tuesday.

"The intensity of the sound is comparable to human speech," said Andrew Fabian of the Institute of Astronomy at Cambridge, England. But the pitch of the sound is about 57 octaves below middle C, roughly the middle of a standard piano keyboard.

This is far, far deeper than humans can hear, the researchers said, and they believe it is the deepest note ever detected in the universe.

The sound is emanating from the Perseus Cluster, a giant clump of galaxies some 250 million light-years from Earth. A light-year is about 6 trillion miles, the distance light travels in a year.

Fabian and his colleagues used NASA's orbiting Chandra X-Ray Observatory to investigate X-rays coming from the cluster's heart. Researchers presumed that a supermassive black hole, with perhaps 2.5 billion times the mass of our sun, lay there, and the activity around the center bolstered this assumption.

Black holes are powerful matter-sucking drains in space, and astronomers believe most galaxies, including our own Milky Way, may contain black holes at their centers. Black holes have not been directly observed, because their gravitational pull is so strong that nothing, not even light, can escape it.

SOUND WAVES

So researchers have concentrated on what happens around the edges of black holes, just before matter is pulled in. When scientists trained the Chandra observatory on the center of Perseus last year, they saw concentric ripples in the cosmic gas that fills the space between the galaxies in the cluster.

"We're dealing with enormous scales here," Fabian said in a telephone interview. "The size of these ripples is 30,000 light-years."

Fabian said the ripples were caused by the rhythmic squeezing and heating of the cosmic gas by the intense gravitational pressure of the jumble of galaxies packed together in the cluster. As the black hole pulls material in, he said, it also creates jets of material shooting out above and below it, and it is these powerful jets that create the pressure that creates the sound waves.

To scientists, he said, pressure ripples equate to sound waves. By calculating how far apart the ripples were, and how fast sound might travel there, the team of researchers determined the musical note of the sound.

Fabian said the notion of singing black holes might well be extrapolated to other galaxies, but not necessarily to the Milky Way.

Chandra has looked at X-ray emissions from the Milky Way's center, and astronomers believe there is a black hole there, but because it is a young, rambunctious galaxy with lots of activity at its heart, this may interfere with any note our black hole might sing, Fabian said.

好像没有加成啊？不知道是怎么回事？

〖华盛顿〗天文学家首次发现黑洞也会“唱歌”。不过，黑洞发出的天籁之音凡人的耳朵根本无法欣赏。它过于低沉，频率只有人耳所能听到的最低声音的上千万亿分之一，是迄今在宇宙中探测到的最低沉的声音。

　　据《华盛顿邮报》１０日报道，英国剑桥天文学研究所费边教授领导的一个小组，利用美国宇航局的“钱德拉”Ｘ射线太空望远镜，探测到了英仙座星系团ＮＧＣ１２５７星系中央一个超大质量黑洞所发出的声波。这个星系团距离地球约２．５亿光年。有关消息发表在英国《皇家天文学会每月通报》上。

　　天文学家们说，如果用音乐术语来表述，这个黑洞发出的是降Ｂ音。它与钢琴上比键盘中央Ｃ音略高的最近一个降Ｂ音键的声音音名相同，但音高却低了５７个八度，或者说频率只及钢琴发出的降Ｂ音的约３００万亿分之一。

　　黑洞是一种体积极小、质量极大的天体，其强大的引力，使得在它周围的区域里连光都无法逃逸。黑洞在吸进物质的同时，也会从中心向外产生两股方向分别相反的物质射流。天文学家们说，正是这些射流导致黑洞发出声波。

　　“钱德拉”望远镜的观测结果显示，来自黑洞的射流压迫英仙座星系团中的气体，结果形成了两个泡沫状的巨大空洞。每个空洞直径约５万光年，它们从黑洞出发向外扩张，像活塞一样不断把星系团中的气体往旁边推，最终形成由空洞向外扩散的巨大声波波纹。

　　“钱德拉”望远镜共观测到这个黑洞产生的多道声波波纹。天文学家们分析后发现，这些波纹间相隔１０００万年的周期。也就是说，该黑洞发出的声波每１０００万年振动一周。据此，天文学家们推算出了黑洞“歌声”的音调等特征。

　　新结果为破解困扰天文学界多年的一个谜团提供了线索。英仙座等星系团中心所包含的高温气体，为什么在近百亿年中一直温度很高，不会冷却，长期以来一直让天文学家们不得其解。费边教授等基于新结果推测说，星系团中的高温气体可能吸收了声波中的能量，从而使高温得以维持。他们说，如果这一推测属实，那将意味着英仙座星系团中央的这个黑洞所“哼唱”出的降Ｂ音，在长达２５亿年中可能都没有发生过什么变化。

　　References:

　　1. 外链出处,Nature Science Update