本帖最后由 gohomeman1 于 2010-1-16 12:35 编辑
http://hubblesite.org/newscenter/archive/releases/2010/05/full/
The full news release story:
新闻全文
Galaxies throughout the universe are ablaze with star birth. But for a nearby, small spiral galaxy, the star-making party is almost over.
遍及宇宙的星系因星暴现象（疯狂诞生恒星的现象）而闪耀，但在我们附近的小型涡旋星系中，星暴盛宴已经快结束了。
Astronomers were surprised to find that star-formation activities in the outer regions of NGC 2976 have been virtually asleep because they shut down millions of years ago. The celebration is confined to a few die-hard partygoers huddled in the galaxy's inner region.
天文学家惊讶地发现，在NGC 2976的外缘，恒星诞生活动已经停顿了数百万年；星暴焰火仅发生在星系内部的少数“顽固”区域中。
The explanation, astronomers say, is that a raucous interaction with a neighboring group of hefty galaxies ignited star birth in NGC 2976. Now the star-making fun is beginning to end. Images from NASA's Hubble Space Telescope show that star formation in the galaxy began fizzling out in its outskirts as some of the gas was stripped away and the rest collapsed toward the center. With no gas left to fuel the party, more and more regions of the galaxy are taking a much-needed nap.
天文学家说，NGC2976中的这些“焰火”是被M81星系团中邻近星系粗暴的引力扰动激发的，现在造星活动已近尾声了。根据哈勃太空望远镜图像，随着气体耗尽，星系中外缘的恒星诞生在5亿年前就逐渐熄灭了，并且迅速向中心传导。由于缺乏新气体点燃恒星焰火，星系中越来越多的区域亟需休眠。
"Astronomers thought that grazing encounters between galaxies can cause the funneling of gas into a galaxy's core, but these Hubble observations provide the clearest view of this phenomenon," explains astronomer Benjamin Williams of the University of Washington in Seattle, who directed the Hubble study, which is part of the ACS Nearby Galaxy Survey Treasury (ANGST) program. "We are catching this galaxy at a very interesting time. Another 500 million years and the party will be over."
ACS邻近星系巡天财政资金项目（ANGST）负责人、华盛顿大学西雅图分校的天文学家本杰明.威廉姆斯解释道：“天文学家认为，星系之间擦身而过将导致气体如漏斗般灌入星系核心，而哈勃图像特别清晰地显示了此现象。我们在一个非常有趣的时间观测了此星系，始于5亿年前的盛宴即将结束。”
NGC 2976 does not look like a typical spiral galaxy. It has a star-forming disk, but no obvious spiral pattern. Its gas is centrally concentrated, but it does not have a central bulge of stars. The galaxy resides on the fringe of the M81 group of galaxies, located about 12 million light-years away in the constellation Ursa Major.
NGC 2976不像典型的涡旋星系：它有一个星暴盘，但看不到旋臂；它的气体浓缩在中心，但中心又没有核球。 它位于大熊星座，离我们约1200万光年，位于M81星系团的边缘。
"The galaxy looks weird because an interaction with the M81 group about a billion years ago stripped some gas from the outer parts of the galaxy, forcing the rest of the gas to rush toward the galaxy's center, where it is has little organized spiral structure," Williams says.
威廉姆斯又说道：“NGC 2976看似比较特异，因为在10亿年前与M81的相互作用，星系外缘的气体被剥离，剩余气体就落向星系中心，因此它几乎没有旋臂结构。”
The tsunami of gas racing toward the center has fueled rapid star birth for at least the past 500 million years in the relatively armless disk. At the same time, star birth ended in the galaxy's outer regions because the gas ran out. Now, the inner disk is running out of gas as new stars burst to life, shrinking the star-birth zone to a 5,000-light-year-wide area around the core.
大约5亿年前，落向中心的气体洪流在缺乏旋臂的星盘中点燃了恒星诞生的风暴；与此同时，星系外缘则因耗尽气体而终止了恒星诞生过程。现在，内盘的气体也渐趋耗尽，星暴区域已经局限于核心附近5000光年范围。
"At one point during this process, the density of gas in the inner regions of this galaxy was very high, about five times higher than it is today," explains Julianne Dalcanton of the University of Washington, and leader of the ANGST team. "The gas vanished incredibly fast, and the galaxy now appears to be settling down."
ANGST团队领队、华盛顿大学的Julianne Dalcanton说：“在这个过程中，星系内部区域的气体密度曾经很高，比现在的高5倍。气体以令人难以置信的速度消耗，星系现在看来已经处于休眠状态。”
Astronomers pieced together this star-formation story with the help of Hubble's sharp vision. The galaxy's relatively close distance to Earth allowed Hubble's Advanced Camera for Surveys (ACS) to resolve hundreds of thousands of individual stars. By studying those stars, the astronomers determined their color and brightness, which provided information about when the stars formed. The astronomers combined the Hubble results with a map, made from radio observations, showing the current distribution of hydrogen across the galaxy. The map is part of The HI Nearby Galaxy Survey by the National Radio Astronomy Observatory's Very Large Array in New Mexico. By analyzing the combined data, Williams and the team then reconstructed the star-making history for large areas of the galaxy.
借助哈勃的高分辨率图像，天文学家拼合了此星系的恒星诞生故事。NGC 2976离地球足够近，哈勃的高级巡天相机（ACS）能够解析出数十万的单个恒星。天文学家研究这些恒星，测定它们的颜色、亮度，从而推断它们的形成信息。然后他们把哈勃数据与该星系的射电图像结合，确定星系中的氢云分布情况。星系的射电图是邻近星系中性氢分布射电巡天图的一部分，由位于新墨西哥州国家射电天文台（NRAO）的甚大射电阵列（VLA）实施。通过对组合数据的分析，威廉姆斯团队重建了此星系大范围的恒星形成历史图像。
"This type of observation is unique to Hubble," Williams says. "If we had not been able to pick out individual stars, we would have known that the galaxy is weird, but we would not have dug up evidence for a significant gas rearrangement in the galaxy, which caused the stellar birth zone to shrink toward the galaxy's center."
威廉姆斯说：“哈勃在这类研究上特别有优势。如果我们不能解析单个恒星，我们就难于了解星系演化（觉得它怪异）。不过我们还没有发掘出星系中气体重新排列的有效证据，是它导致了恒星诞生区收缩到核心区。”
Simulations predict that the same "gas-funneling" mechanism may trigger starbursts in the central regions of other dwarf galaxies that interact with larger neighbors. The trick to studying the effects of this process in detail, Williams says, is being able to resolve many individual stars in galaxies to create an accurate picture of their evolution.
模型预测：当矮星系受到大邻居星系的引力扰动时，类似“气体漏斗”机制会导致核心区的星暴现象。威廉姆斯最后说，随着我们研究这些过程效应渐趋详细，我们能分辨星系中单个恒星的数量越多，星系的演化图像就越精确。
Williams' results will appear in the January 20, 2010 issue of The Astrophysical Journal.
威廉姆斯团队的研究报告将刊登在2010.1.20出版的《天体物理学》期刊上。
CONTACT
相关联系人
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
马里兰州巴尔的摩市，太空望远镜科研所
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Benjamin Williams
University of Washington, Seattle, WA
华盛顿州，华盛顿大学西雅图分校
206-543-9849
ben@astro.washington.edu |
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