设为首页收藏本站加入QQ群

天之文天文论坛

 找回密码
 用户注册——开始天之文生活

QQ登录

只需一步,快速开始

扫一扫,访问微社区

查看: 1758|回复: 5

[E文大家看]对M15中心存在“中等质量黑洞”的质疑(译文已发布,请看跟贴)

[复制链接]
发表于 2003-1-14 16:33 | 显示全部楼层 |阅读模式
分享到:
[这个贴子最后由Shea在 2003/01/28 04:49pm 编辑]

对M15中心存在“中等质量黑洞”的质疑
节选自文献:
Irion R., "The Milky Way's Restless Swarms of Stars", Science, 2003, 299, 5603, 60-62.
Another cluster mystery lies at the center of a swirling debate: What lurks at the innermost core? NASA alluded to this in a press conference in September touting a major discovery by HST: "intermediate-mass black holes" at the centers of two clusters, M15 in our Milky Way and G1 in the neighboring Andromeda galaxy. Weighing in at thousands of times the mass of our sun, these black holes were a putative steppingstone between smaller black holes formed by supernovas and titanic ones at the cores of galaxies. Today, astronomers are standing by their claim for a black hole in G1, but the M15 result has eroded into statistical insignificance.
To identify the suspected midsize black holes, astronomers used HST to measure the orbital speeds of stars at the clusters' cores. Rapid orbits suggested that the gravity of some dark, hidden mass was pulling stars into unexpectedly fast whirls around the centers. But there's a catch: Other compact objects at the center could produce the same dynamics--for example, thousands of neutron stars within a small volume of space. Such nests are improbable in most places. However, they could arise in globular clusters, where massive objects quickly settle to the center like heavier molecules at the base of Earth's atmosphere.
For M15, the HST astronomers relied on an earlier estimate of the number of neutron stars in the cluster. The relatively low figure allowed them to state with confidence that neutron stars alone could not explain the star motions they saw. Only later did the researchers determine that the figure they had adopted was three to five times too low. "We could no longer rule out the no-black-hole case" with the extra neutron stars, says astronomer Karl Gebhardt of the University of Texas, Austin.
That backtracking didn't surprise Hut, Portegies Zwart, and their colleagues, who conducted GRAPE simulations of an M15-like cluster with 128,000 particles. In the 1 January issue of Astrophysical Journal Letters, the team reports that M15 probably contains a dense warren of small black holes and neutron stars, all orbiting near the center. For an intermediate-mass black hole to arise, they claim, a cluster's giant stars must merge quickly in their youths, when they are bloated and more likely to crash. Once the stars blow up after about 10 million years to forge black holes and neutron stars, assembling a bunch of them becomes much more difficult. "Compact objects are so tiny that they almost never collide once they form," Portegies Zwart says. "They kick each other out of the cluster rather than merge into something bigger."
The debate is far from over. Gebhardt has data in hand from a ground-based survey of star motions in about 15 other Milky Way clusters, most of them easier to study than the crowded heart of M15. His analysis, forthcoming within a few months, suggests that intermediate-mass black holes may yet prove to be the best explanation. "I'm getting much more convinced now that this is a reality," he says. "But I realize it will be an uphill battle for me to convince others."
 楼主| 发表于 2003-1-23 14:01 | 显示全部楼层

[E文大家看]对M15中心存在“中等质量黑洞”的质疑(译文已发布,请看跟贴)

此贴作为“E文大家看”的试点,如果有问题还请大家踊跃提问,
译文将于1月30日公布。
发表于 2003-1-24 18:55 | 显示全部楼层

[E文大家看]对M15中心存在“中等质量黑洞”的质疑(译文已发布,请看跟贴)

我知道m87有个20亿个太阳质量的黑洞!!!!
 楼主| 发表于 2003-1-26 09:52 | 显示全部楼层

[E文大家看]对M15中心存在“中等质量黑洞”的质疑(译文已发布,请看跟贴)

但是值得注意的是,M87是一个星系,而M15是一个球状星团。
 楼主| 发表于 2003-1-28 16:46 | 显示全部楼层

[E文大家看]对M15中心存在“中等质量黑洞”的质疑(译文已发布,请看跟贴)

译文:
另一个谜是,球状星团的核心到底是什么?NASA9月份公布的哈勃空间望远镜的发现认为球状星团M15和G1的核心是“中等质量黑洞”。这些黑洞的质量大约是太阳质量的书千倍,介于恒星质量黑洞和超大质量黑洞之间。现在,天文学家对于G1中心有黑洞没有异议,但是对于有关M15的结论择优一些疑义。
为了认证中等质量黑洞的存在,天文学家使用哈勃空间望远镜来测量星团核心区域恒星的运动速度。极高的轨道速度预示着一些不可见的物质加速了恒星。但是还有一个问题,其他位于中心的致密天体也能产生同样效果,例如在小范围内的上千颗中子星。这么多的中子星未必会在其他地方出现,但是在球状星团中则是完全可能的。因为在球状星团中大质量的天体很快就会进入星团的核心区域,就橡较重的分子总是位于地球大气层的底部一样。
对于M15,哈勃空间望远镜的结论建立在早期对其中中子星数量的估计之上。相对少的数量使得他们很有信心的认为中子星不足以解释观测到的现象。直到后来,其他天文学家发现这一估计值偏小了3-5倍。“我们无法排除只有大量中子星而没有黑洞的情况了,”德克萨斯大学的天文学家卡尔·吉布哈特(Karl Gebhardt) 说。
这一反复到并没有使得哈特、波特杰斯·兹瓦尔特和他们的同事感到吃惊。他们使用GRAPE,对于M15这一类型的球状星团进行了模拟。在1月1日出版的《天体物理学报通信》上,他们的小组报告,M15核心处可能会有大量的小黑洞和中子星。若要存在一个中等质量黑洞,他们认为,星团中的巨星必须在年轻时就快速的合并。一旦恒星爆发形成了黑洞和中子星就很难在发生碰撞合并。“致密天体非常的少,他们形成之后几乎不可能发生碰撞,”波特杰斯·兹瓦尔特说,“他们会把其他的天体抛射出星团,而不是与他们合并形成更大的天体。”
争论还远没有结束。吉布哈特手中有地面观测的其他15个球状星团中恒星运动的数据资料,其中大部分的核心没有M15那么稠密。他的分析(将于几个月之后公布)显示中等质量黑洞将是最好的解释。“我现在越来越相信这是事实,”他说,“但是我意识到这很难让别人相信。”
发表于 2003-1-30 15:32 | 显示全部楼层

[E文大家看]对M15中心存在“中等质量黑洞”的质疑(译文已发布,请看跟贴)

这么长的文章我即使是全神贯注的搞没两三个小时还是搞不定的!看来我还是要努力啊!

本版积分规则

小黑屋|手机版|Archiver|中国天文科普网-天之文天文论坛-中国科学院优秀科普网站 ( 沪ICP备05005481号-2   点击这里加入此群

GMT+8, 2019-9-20 09:57 , Processed in 0.277146 second(s), 12 queries , Xcache On.

Powered by Discuz! X3.2 Licensed

© 2001-2013 Comsenz Inc.

快速回复 返回顶部 返回列表