本帖最后由 gohomeman1 于 2009-5-11 10:42 编辑
http://hubblesite.org/newscenter/archive/releases/2009/08/full/
The full news release story:
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Whatever dark energy is, explanations for it have less wiggle room following a Hubble Space Telescope observation that has refined the measurement of the universe's present expansion rate to a precision where the error is smaller than five percent. The new value for the expansion rate, known as the Hubble constant, or H0 (after Edwin Hubble who first measured the expansion of the universe nearly a century ago), is 74.2 kilometers per second per megaparsec (error margin of ± 3.6). The results agree closely with an earlier measurement gleaned from Hubble of 72 ± 8 km/sec/megaparsec, but are now more than twice as precise.
无论暗能量是什么，对它的解释总是不能离开当前宇宙的膨胀速率的，而根据哈勃太空望远镜的观测数据，这个数据的测量精度误差已经小于5%。最新的宇宙膨胀速率数值——我们称为哈勃常数H0，是(74.2± 3.6)km/(s*Mpc),即每百万秒差距下（74.2± 3.6）km/s。此数据离埃德温.哈勃首次测量宇宙膨胀速率都快一个世纪了。此数据与此前哈勃数据测定的（72±8）km/s/Mpc相当一致，但现在的精度提高了一倍。
The Hubble measurement, conducted by the SHOES (Supernova H0 for the Equation of State) Team and led by Adam Riess, of the Space Telescope Science Institute and the Johns Hopkins University, uses a number of refinements to streamline and strengthen the construction of a cosmic "distance ladder," a billion light-years in length, that astronomers use to determine the universe's expansion rate.
亚当·瑞斯，（马里兰州）约翰霍普金斯大学教授、太空望远镜科学研究所研究员。由他牵头的超新星H0状态方程式（简称SHOES）测量团队，运用许多简化方法和加强精度的手法处理哈勃望远镜的观测数据，构建了宇宙“距离台阶”，（精确测量了）10亿光年的距离，从而确定了宇宙膨胀速度。
Hubble observations of pulsating stars called Cepheid variables in a nearby cosmic mile marker, the galaxy NGC 4258, and in the host galaxies of recent supernovae, directly link these distance indicators.The use of Hubble to bridge these rungs in the ladder eliminated the systematic errors that are almost unavoidably introduced by comparing measurements from different telescopes.
哈勃望远镜观测了一个近距离的星系NGC 4258中一类被称为造父变星的脉动变星和当前的超新星，直接比对了这些距离指示器。使用哈勃望远镜构建这些距离台阶的好处是能消除使用不同望远镜比较数据时几乎必然产生的系统误差。
Riess explains the new technique: "It's like measuring a building with a long tape measure instead of moving a yard stick end over end.You avoid compounding the little errors you make every time you move the yardstick. The higher the building, the greater the error."
亚当.瑞斯解释了这个新手法：“这就像测量一个建筑，用长卷尺取代短码尺一段又一段的量（，精度高多了）。你避免了每次移动短尺时的小误差的累积。建筑越高，累积误差越大。”
Lucas Macri, professor of physics and astronomy at Texas A&M,and a significant contributor to the results, said, "Cepheids are the backbone of the distance ladder because their pulsation periods, which are easily observed, correlate directly with their luminosities.Another refinement of our ladder is the fact that we have observed the Cepheids in the near-infrared parts of the electromagnetic spectrum where these variable stars are better distance indicators than at optical wavelengths."
本文的另一位重要撰稿人，美国德克萨斯A&M大学教授卢卡斯.马克里说：“造父变星成为距离台阶的支柱，是因为它们的脉动周期很容量测定，而且与它们的绝对光度有直接的关系。我们这些距离台阶的另一个改进是：我们已经观测了造父变星的近红外波谱，这些变星在红外电磁波段的量天尺性能比可见光波段更好”。
This new, more precise value of the Hubble constant was used to test and constrain the properties of dark energy, the form of energy that produces a repulsive force in space, which is causing the expansion rate of the universe to accelerate.
新的更精确的哈勃常数用于测试和约束暗能量的属性：一种导致（当前）宇宙加速膨胀、能产生斥力的（未知）能量。
By bracketing the expansion history of the universe between today and when the universe was only approximately 380,000 years old, the astronomers were able to place limits on the nature of the dark energy that is causing the expansion to speed up. (The measurement for the far, early universe is derived from fluctuations in the cosmic microwave background, as resolved by NASA's Wilkinson Microwave Anisotropy Probe, WMAP, in 2003.)
对比宇宙当前与年仅38万岁时的膨胀速率，天文学家能够界定正是暗能量的性质导致宇宙加速膨胀。对遥远的早期宇宙的测量源自宇宙背景微波辐射的微小起伏，数据来自2003年NASA的威尔金森宇宙微波各向异性探测卫星（WMAP）的观测结果。
Their result is consistent with the simplest interpretation of dark energy: that it is mathematically equivalent to Albert Einstein'shypothesized cosmological constant, introduced a century ago to push on the fabric of space and prevent the universe from collapsing under the pull of gravity. (Einstein, however, removed the constant once the expansion of the universe was discovered by Edwin Hubble.)
他们的结果与对暗能量的最简单解释一致：它与阿尔伯特.爱因斯坦的宇宙学常数猜想在数学上相当，一个世纪前他引入斥力概念以对抗万有引力的收缩作用，维持宇宙的结构。（当埃德温.哈勃发现宇宙膨胀后，爱因斯坦就放弃了宇宙学常数。）
"If you put in a box all the ways that dark energy might differ from the cosmological constant, that box would now be three times smaller,"says Riess. "That's progress, but we still have a long way to go to pindown the nature of dark energy."
亚当·瑞斯说：“如果你一直用盒子来表示暗能量与宇宙学常数的区别，那么现在盒子已经缩小了3倍。这是一个进步，但离彻底确定暗能量的属性还有很长的路要走。”
Though the cosmological constant was conceived of long ago,observational evidence for dark energy didn't come along until 11 years ago, when two studies, one led by Riess and Brian Schmidt of MountStromlo Observatory, and the other by Saul Perlmutter of Lawrence Berkeley National Laboratory, discovered dark energy independently, inpart with Hubble observations. Since then astronomers have been pursuing observations to better characterize dark energy.
虽然宇宙学常数已经提出许多年，暗能量的观测证据却姗姗来迟。直到11年前，两个研究团队各自独立发现了暗能量；此后，天文学家持续观测以更好的描述暗能量。这2个团队是：由约翰霍普金斯大学教授、太空望远镜科学研究所研究员的亚当·瑞斯和（澳洲）史创罗峰天文台的布莱．施米兹牵头的国际团队，以及（加州）劳伦斯·伯克利国家实验室的索尔‧普密特团队。
Riess's approach to narrowing alternative explanations for darkenergy—whether it is a static cosmological constant or a dynamical field (like the repulsive force that drove inflation after the big bang)—is to further refine measurements of the universe's expansion history.
亚当·瑞斯团队已经缩小了暗能量解释的选择面——无论它是一个固定的宇宙学常数还是有个动态范围（就像宇宙大爆炸后驱使宇宙膨胀的斥力那样）——都更精准地测量了宇宙膨胀历史。
Before Hubble was launched in 1990, the estimates of the Hubble constant varied by a factor of two. In the late 1990s the Hubble Space Telescope Key Project on the Extragalactic Distance Scale refined the value of the Hubble constant to an error of only about ten percent.This was accomplished by observing Cepheid variables at optical wavelengths out to greater distances than obtained previously and comparing those to similar measurements from ground-based telescopes.
在哈勃望远镜1990年发射前，哈勃常数的估值受计算因子该取1还是2的影响而各不相同。20世纪90年代，哈勃太空望远镜重点项目——外银河系距离标尺工程把哈勃常数的误差缩小到10%左右。这是通过观测比先前远得多的造父变星的可见光谱实现的，结果与地面望远镜观测结论类似。
The SHOES team used Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) and the Advanced Camera for Surveys (ACS) to observe 240 Cepheid variable stars across seven galaxies. One of these galaxies was NGC 4258, whose distance was very accurately determined through observations with radio telescopes. The other six galaxies recently hosted Type Ia supernovae that are reliable distance indicators for even farther measurements in the universe. Type Ia supernovae all explode with nearly the same amount of energy and therefore have almost the same intrinsic brightness.
SHOES团队使用哈勃望远镜的近红外相机和多目标光谱仪（NICMOS）、高级巡天相机（ACS）观测了综括7个星系的240颗造父变星。其中的一个星系是NGC 4258，它的距离已经由射电望远镜阵列非常精确的测量过。其他6个星系最近都爆发了Ia型超新星——测量遥远宇宙距离时更可靠的量天尺。Ia超新星爆发时辐射的能量几乎相等，因而具有几乎相同的本征亮度。（Ia超新星的光谱特征非常明显，其最大光度约-19.3等——译注)
By observing Cepheids with very similar properties at near-infrared wavelengths in all seven galaxies, and using the same telescope and instrument, the team was able to more precisely calibrate the luminosity of supernovae. With Hubble's powerful capabilities, the team was able to side step some of the shakiest rungs along the previous distance ladder involving uncertainties in the behavior of Cepheids.
通过很相似的方法，在全部7个星系中用相同的（哈勃）望远镜和仪器，在近红外波段观测造父变星和超新星，团队能够更加精确地校准Ia超新星的光度。有了哈勃望远镜的强大能力，团队就能直接跨过某些不稳定的台阶：（由于清晰度不够，）先前对这些造父变星行为的观测不是很准确。
Riess would eventually like to see the Hubble constant refined to a value with an error of no more than one percent, to put even tighter constraints on solutions to dark energy.
最后，亚当·瑞斯很想看到未来哈勃常数的精度误差小于1%，从而尽可能逼近暗能量的真实解答。
CONTACT
联系人
Ray Villard
雷·维兰德
Space Telescope Science Institute, Baltimore, Md.
马里兰州 巴尔的摩市 太空望远镜科学研究所
410-338-4514
villard@stsci.edu
Adam Riess
亚当·瑞斯
Space Telescope Science Institute/Johns Hopkins University, Baltimore, Md.
马里兰州 巴尔的摩市 太空望远镜科学研究所/约翰霍普金斯大学
410-516-4474
ariess@stsci.edu |
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