“哈勃”发现了一个特别而又强大的星系英文原文
译:Jack

   
    就像巫婆的一个大炉子向外呼呼的冒漩涡状的热气一样,这个活跃的星系的中心仿佛黑洞一样的强大。这个星系座落在距我们1300万光年的圆规座内。这个星系向我们展示了第二类赛费特星系:这一类星系即有紧密中心一类的星系,人们相信,它们的中心存在大量的黑洞。其实,赛费特星系本身就是被称作是有AGN(活跃的星系中心)的一类星系的一部分。AGN有以高速将气体吹出星系中心的能力。研究圆规座星系的天文学家们同样也发现图片中显示的这个星系有AGN。

    在圆规座的漩涡星系中的大部分气体都与两个具体的“环”有密切的联系。那个较大的,直径大约有1,300光年,它已经被地基望远镜观测到了。而先前,我们没有观测到的那个小“环”,直径大约有260光年。

    从图片上看来,那个直径较小的、较不明显的环,处于那个黑色的“盘”地内部,而大的那个则在星系盘面上延伸。(点击到大图片)
                                 

    当然,两个“环”和那些主要的星体爆发(下简称“星爆”)的区域一样,都是大量的气体和灰尘的依附之处。那些星爆区域中,恒星快速地形成,例如在4,000万年~15,000万年之间(虽然这样的时间对我们来说是太长了,但是这个时间和星系的年龄比起来,是在是太短了)。

    人们相信,在赛费特星系的中心,存在黑洞,依据就是环绕着星系的气体和灰尘。黑洞和它依附的盘正在将气体排出星系盘,直到将它们推到“晕”(处于星系盘上边和下边的部分)中。气体的详细的结构则可以在图片中的紫色的、向上延伸的部分看清。

    星系的中心或者说是内部的星爆环是一个“V”字形的气体结构。这个气体结构在这张复合而成的图片中显略带白色的粉红色。我们所以说这张图片是复合而成的,是因为它是经四个滤镜处理过的。其中的两个滤镜滤掉了氧和氢原子在电子跃迁的过程中,发出的窄线。而另外两个宽滤镜则是消去了绿光和接近红外线的射线。通过狭窄的滤镜,“V”字形的结构显得十分清晰:一个三维锥体的投影的区域从这个星系的中心一直延伸到星系的晕,当然,在这个锥体里,包含着被依附着的黑洞的辐射所加热的气体。人们相信,所谓的“反锥体”的存在,但是,它由于灰尘的影响,在星系盘中显得很模糊。在星系的中心所发射出的紫外辐射激发了中心附近的气体,使其增长。就像巨大两盏探照灯,激发后的气体被定向发射到反锥体中。

    由于靠近银盘的附近,圆规座星系就被灰尘部分的遮挡了。结果,我们从前未对这个星系大加注意,知道约25年以前。

   译自 摘自哈勃网站(http://oposite.stsci.edu

A Hubble Captures an Extraordinary and Powerful Active Galaxy
Chinese Version


  Resembling a swirling witch's cauldron of glowing vapors, the black hole-powered core of a nearby active galaxy appears in this colorful NASA Hubble Space Telescope image. The galaxy lies 13 million light-years away in the southern constellation Circinus.

  This galaxy is designated a type 2 Seyfert, a class of mostly spiral galaxies that have compact centers and are believed to contain massive black holes. Seyfert galaxies are themselves part of a larger class of objects called Active Galactic Nuclei or AGN. AGN have the ability to remove gas from the centers of their galaxies by blowing it out into space at phenomenal speeds. Astronomers studying the Circinus galaxy are seeing evidence of a powerful AGN at the center of this galaxy as well.

  Much of the gas in the disk of the Circinus spiral is concentrated in two specific rings -- a larger one of diameter 1,300 light-years, which has already been observed by ground-based telescopes, and a previously unseen ring of diameter 260 light-years.

  In the Hubble image, the smaller inner ring is located on the inside of the green disk. The larger outer ring extends off the image and is in the plane of the galaxy's disk. Both rings are home to large amounts of gas and dust as well as areas of major "starburst" activity, where new stars are rapidly forming on timescales of 40 - 150 million years, much shorter than the age of the entire galaxy.

  At the center of the starburst rings is the Seyfert nucleus, the believed signature of a supermassive black hole that is accreting surrounding gas and dust. The black hole and its accretion disk are expelling gas out of the galaxy's disk and into its halo (the region above and below the disk). The detailed structure of this gas is seen as magenta-colored streamers extending towards the top of the image.

  In the center of the galaxy and within the inner starburst ring is a V-shaped structure of gas. The structure appears whitish-pink in this composite image, made up of four filters. Two filters capture the narrow lines from atomic transitions in oxygen and hydrogen; two wider filters detect green and near-infrared light. In the narrow-band filters, the V-shaped structure is very pronounced. This region, which is the projection of a three-dimensional cone extending from the nucleus to the galaxy's halo, contains gas that has been heated by radiation emitted by the accreting black hole. A "counter-cone," believed to be present, is obscured from view by dust in the galaxy's disk. Ultraviolet radiation emerging from the central source excites nearby gas causing it to glow. The excited gas is beamed into the oppositely directed cones like two giant searchlights.

  Located near the plane of our own Milky Way Galaxy, the Circinus galaxy is partially hidden by intervening dust along our line of sight. As a result, the galaxy went unnoticed until about 25 years ago. This Hubble image was taken on April 10, 1999 with the Wide Field Planetary Camera 2.

  The research team, led by Andrew S. Wilson of the University of Maryland, is using these visible light images along with near-infrared data to further understand the dynamics of this powerful galaxy.

   Copied From Hubble Web(http://oposite.stsci.edu

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