Direct detection of pulsations of the Cepheid star zeta Gem and an independent calibration of the period-luminosity relation

Cepheids are a class of variable (pulsating) stars whose absolute luminosities are related in a simple manner to their pulsational periods. By measuring the period and using the 'period-luminosity' relationship, astronomers can use the observed visual brightness to determine the distance to the star. Because these stars are very luminous, they can be observed in other galaxies, and therefore can be used to help determine the expansion rate of the Universe (the Hubble constant). Calibration of the period-luminosity relation is a necessary first step, but the small number of sufficiently nearby Cepheids has forced the use of a number of indirect means, with associated systematic uncertainties. Here we present a distance to the Cepheid zeta Geminorum, determined using a direct measurement (by an optical interferometer) of its changes in diameter as it pulsates. Within our uncertainty of 15 per cent, our distance is in agreement with previous indirect determinations. Planned improvements to the instrument will allow us to calibrate directly the period-luminosity relation to better than a few per cent.     

The dynamical mass of a classical Cepheid variable star in an eclipsing binary system

Stellar pulsation theory provides a means of determining the masses of pulsating classical Cepheid supergiants-it is the pulsation that causes their luminosity to vary. Such pulsational masses are found to be smaller than the masses derived from stellar evolution theory: this is the Cepheid mass discrepancy problem, for which a solution is missing. An independent, accurate dynamical mass determination for a classical Cepheid variable star (as opposed to type-II Cepheids, low-mass stars with a very different evolutionary history) in a binary system is needed in order to determine which is correct. The accuracy of previous efforts to establish a dynamical Cepheid mass from Galactic single-lined non-eclipsing binaries was typically about 15-30% (refs 6, 7), which is not good enough to resolve the mass discrepancy problem. In spite of many observational efforts, no firm detection of a classical Cepheid in an eclipsing double-lined binary has hitherto been reported. Here we report the discovery of a classical Cepheid in a well detached, double-lined eclipsing binary in the Large Magellanic Cloud. We determine the mass to a precision of 1% and show that it agrees with its pulsation mass, providing strong evidence that pulsation theory correctly and precisely predicts the masses of classical Cepheids.     

Three classical Cepheid variable stars in the nuclear bulge of the Milky Way

The nuclear bulge is a region with a radius of about 200 parsecs around the centre of the Milky Way. It contains stars with ages ranging from a few million years to over a billion years, yet its star-formation history and the triggering process for star formation remain to be resolved. Recently, episodic star formation, powered by changes in the gas content, has been suggested. Classical Cepheid variable stars have pulsation periods that decrease with increasing age, so it is possible to probe the star-formation history on the basis of the distribution of their periods. Here we report the presence of three classical Cepheids in the nuclear bulge with pulsation periods of approximately 20?days, within 40 parsecs (projected distance) of the central black hole. No Cepheids with longer or shorter periods were found. We infer that there was a period about 25 million years ago, and possibly lasting until recently, in which star formation increased relative to the period of 30-70 million years ago.     

Discovery of the short gamma-ray burst GRB 050709

Gamma-ray bursts (GRBs) fall into two classes: short-hard and long-soft bursts. The latter are now known to have X-ray and optical afterglows, to occur at cosmological distances in star-forming galaxies, and to be associated with the explosion of massive stars. In contrast, the distance scale, the energy scale and the progenitors of the short bursts have remained a mystery. Here we report the discovery of a short-hard burst whose accurate localization has led to follow-up observations that have identified the X-ray afterglow and (for the first time) the optical afterglow of a short-hard burst; this in turn led to the identification of the host galaxy of the burst as a late-type galaxy at z = 0.16 (ref. 10). These results show that at least some short-hard bursts occur at cosmological distances in the outskirts of galaxies, and are likely to be caused by the merging of compact binaries.     

A close nuclear black-hole pair in the spiral galaxy NGC 3393

The current picture of galaxy evolution advocates co-evolution of galaxies and their nuclear massive black holes, through accretion and galactic merging. Pairs of quasars, each with a massive black hole at the centre of its galaxy, have separations of 6,000 to 300,000 light years (refs 2 and 3; 1 parsec = 3.26 light years) and exemplify the first stages of this gravitational interaction. The final stages of the black-hole merging process, through binary black holes and final collapse into a single black hole with gravitational wave emission, are consistent with the sub-light-year separation inferred from the optical spectra and light-variability of two such quasars. The double active nuclei of a few nearby galaxies with disrupted morphology and intense star formation (such as NGC 6240 with a separation of about 2,600 light years and Mrk 463 with a separation of about 13,000 light years between the nuclei) demonstrate the importance of major mergers of equal-mass spiral galaxies in this evolution; such mergers lead to an elliptical galaxy, as in the case of the double-radio-nucleus elliptical galaxy 0402+379 (with a separation of about 24 light years between the nuclei). Minor mergers of a spiral galaxy with a smaller companion should be a more common occurrence, evolving into spiral galaxies with active massive black-hole pairs, but have hitherto not been seen. Here we report the presence of two active massive black holes, separated by about 490 light years, in the Seyfert galaxy NGC 3393 (50 Mpc, about 160 million light years). The regular spiral morphology and predominantly old circum-nuclear stellar population of this galaxy, and the closeness of the black holes embedded in the bulge, provide a hitherto missing observational point to the study of galaxy/black hole evolution. Comparison of our observations with current theoretical models of mergers suggests that they are the result of minor merger evolution.     

A candidate redshift z ≈ 10 galaxy and rapid changes in that population at an age of 500 Myr

Searches for very-high-redshift galaxies over the past decade have yielded a large sample of more than 6,000 galaxies existing just 900-2,000?million years (Myr) after the Big Bang (redshifts 6?>?z?>?3; ref. 1). The Hubble Ultra Deep Field (HUDF09) data have yielded the first reliable detections of z?≈?8 galaxies that, together with reports of a γ-ray burst at z?≈?8.2 (refs 10, 11), constitute the earliest objects reliably reported to date. Observations of z?≈?7-8 galaxies suggest substantial star formation at z?>?9-10 (refs 12, 13). Here we use the full two-year HUDF09 data to conduct an ultra-deep search for z?≈?10 galaxies in the heart of the reionization epoch, only 500?Myr after the Big Bang. Not only do we find one possible z?≈?10 galaxy candidate, but we show that, regardless of source detections, the star formation rate density is much smaller (～10%) at this time than it is just ～200?Myr later at z?≈?8. This demonstrates how rapid galaxy build-up was at z?≈?10, as galaxies increased in both luminosity density and volume density from z?≈?10 to z?≈?8. The 100-200?Myr before z?≈?10 is clearly a crucial phase in the assembly of the earliest galaxies.     

Galaxy mass deduced from the structure of Einstein ring MG1654+1346

ELLIPTICAL galaxies acting as gravitational lenses occasionally produce spectacular images-Einstein rings-of distant objects. Giant arcs(1) and radio rings(2) have been observed. A wide variety of image morphologies is possible, the generation of which is qualitatively understood in terms of large magnifications at caustic and critical lines in the lensing geometry(3-5). From the angular size of the image, and with knowledge of the distances of the lensed and lensing object, rough estimates of the mass of the lensing galaxy can be obtained. We have made high-resolution radio-interferometric observations of MG1654 + 1346 (ref. 6) a radio quasar in near-perfect alignment with an elliptical galaxy, and show that radio emission is distorted into a narrow Einstein ring that lies within a diamond-shaped region bounded by caustic lines. From the details of the ring structure, a new model for the lensing geometry is deduced which leads to a more accurate estimate of the mass of the lensing galaxy.     

土压实度的瞬态冲击法测试

为寻找一种无损、快速和准确地检测土压实度的新方法,基于振动能量在土壤中衰减的基本原理,使用重锤冲击压实度不同、含水质量分数不同的土壤,在与冲击点一定距离处的土壤中测取振动响应信号,并对测取的信号在时域和频域上进行分析。试验结果表明:在测试距离一定、含水质量分数相同时,在同一脉冲宽度内振动加速度信号的幅值、有效值均随压实度的增加而增大;在最佳含水质量分数附近的范围内,土壤中含水质量分数对压实度计算结果的影响不大,误差小于1%;在冲击距离为200~400 mm时的测量和计算结果,比较接近真实测量值,距离较近、较远时误差均较大。     

关于宇宙膨胀的密度时间曲线的经典理论计算

按宇宙在大尺度上均匀、各向同性的假设,运用经典力学理论,由质量连续性定理和牛顿第二定律,计算哈勃常数与宇宙膨胀时间的关系以及宇宙质量密度、宇宙尺度与宇宙膨胀时间的关系.哈勃常数的计算结果与观察结果相符.     

超新星的最新统计分析

用最新的Ａｓｉａｇｏ超新星表和ＲＣ３星系表分析了各类超新星在不同哈勃型星系中的分布;考虑了Ｉａ型超新星的峰值光度同光变曲线下降率的关系后,得出的哈常数值误差较小,表明近星系Ｉａ型超新星仍是一个较好的距离指示器;分析了高红移超新星宇宙学的紧密联系。     

A measurement of the cosmological mass density from clustering in the 2dF Galaxy Redshift Survey

The large-scale structure in the distribution of galaxies is thought to arise from the gravitational instability of small fluctuations in the initial density field of the Universe. A key test of this hypothesis is that forming superclusters of galaxies should generate a systematic infall of other galaxies. This would be evident in the pattern of recessional velocities, causing an anisotropy in the inferred spatial clustering of galaxies. Here we report a precise measurement of this clustering, using the redshifts of more than 141,000 galaxies from the two-degree-field (2dF) galaxy redshift survey. We determine the parameter beta = Omega0.6/b = 0.43 +/- 0.07, where Omega is the total mass-density parameter of the Universe and b is a measure of the 'bias' of the luminous galaxies in the survey. (Bias is the difference between the clustering of visible galaxies and of the total mass, most of which is dark.) Combined with the anisotropy of the cosmic microwave background, our results favour a low-density Universe with Omega approximately 0.3.     

Suppression of dwarf galaxy formation by cosmic reionization

A large number of faint galaxies, born less than a billion years after the Big Bang, have recently been discovered. Fluctuations in the distribution of these galaxies contributed to a scatter in the ionization fraction of cosmic hydrogen on scales of tens of megaparsecs, as observed along the lines of sight to the earliest known quasars. Theoretical simulations predict that the formation of dwarf galaxies should have been suppressed after cosmic hydrogen was reionized, leading to a drop in the cosmic star-formation rate. Here we report evidence for this suppression. We show that the post-reionization galaxies that produced most of the ionizing radiation at a redshift z approximately 5.5 must have had a mass in excess of approximately 10(10.9 +/- 0.5) solar masses (M(o)) or else the aforementioned scatter would have been smaller than observed. This limiting mass is two orders of magnitude larger than the galaxy mass that is thought to have dominated the reionization of cosmic hydrogen (approximately 10(8) M(o)). We predict that future surveys with space-based infrared telescopes will detect a population of smaller galaxies that reionized the Universe at an earlier time, before the epoch of dwarf galaxy suppression.     

对宇观天体和微观粒子质量-半径统一计算的注记

 以宇观天体、“多成分宇宙”中稳定粒子质量和半径的统一计算结果为基础,进而对Dirac大数D;中微子“反常荷”和“反常磁矩”;最重的玻色子与最轻的费米子相互关联;混沌理论的菲根鲍姆常数δ以及哈勃常数H作了分析计算,所得结果与实验数据或惯用值很好相符.说明由宇宙演化的两类自由流阻尼标度导出的宇观天体、微观粒子的质量和半径统一计算公式是正确的.     

传输距离对实际量子密钥分发系统的影响

基于BB84协议原理,搭建偏振编码的长距离点对点实际量子密钥分发实验系统.利用该实验平台完成了5,10,15km 3种不同传输距离的量子密钥分发实验,并对系统主要参数实时采集进行数据分析.实验结果表明:随着发送端与接收端量子光纤信道距离的增加,在统计时间内,系统分段成码率降低,信号态和诱骗态误码率上升,系统产生的密钥量降低.     

总星系中“暗质量”形成和分布的基本规律及与“真空背景微波辐射”、“宇宙常数”的因果关联

本文应用相对论性牛顿万有引力定律和非黎曼几何的传统力学分析方法,定量导出和证明了总星系中场"暗质量""、暗能量"的形成、演化和各向同性均匀分布的基本规律,得到了场"暗质量"密度"、暗能量"密度理论值;定量导出了总星系中场"暗质量"密度"、暗能量"密度与"真空背景微波辐射""、宇宙常数"的因果关联,求得了真空背景微波辐射温度和宇宙常数理论值,所得系列理论结果,与已有观测事实极相吻合.     

Cosmological tests of general relativity

General relativity theory could be tested on a cosmological scale by measuring the Hubble constant and the deceleration parameter, if, in addition, everything could be known about the matter filling the universe. If, on the other hand, nothing could be presupposed about the matter content of the universe, general relativity could not be tested by measuring any number of time derivatives of the scale factor. But upon making the assumption of a universe filled with a non-interacting mixture of non-relativistic matter and radiation we can in principle test general relativity by measuring the first five derivatives of the scale factor. In the following, some general relations are presented using this assumption.     

Mitochondria1 cytochromeb sequences variation of Protura and molecular systematics of Apterygota

Mitochondrial cytochromeb genes of about 450 bp fragments from 3 proturan species, 5 collembolan species and 2 dipluran species have been sequenced. The number of nucleotide substitutions and Kimura 2-parameter distances have also been calculated, and a series of molecular phylogenetic trees reconstructed by using parsimony and distance methods. The proturan, collembolan and dipluran species have evolved monophyletic groups. The results suggest that Protura and Collembola are sister groups, while Diplura is more or less demonstrating a closer phylogenetic relationship to the pterygotan insects. The phylogeny and their systematic position of protura and other groups are also discussed.     

Two ten-billion-solar-mass black holes at the centres of giant elliptical galaxies

Observational work conducted over the past few decades indicates that all massive galaxies have supermassive black holes at their centres. Although the luminosities and brightness fluctuations of quasars in the early Universe suggest that some were powered by black holes with masses greater than 10 billion solar masses, the remnants of these objects have not been found in the nearby Universe. The giant elliptical galaxy Messier 87 hosts the hitherto most massive known black hole, which has a mass of 6.3 billion solar masses. Here we report that NGC 3842, the brightest galaxy in a cluster at a distance from Earth of 98 megaparsecs, has a central black hole with a mass of 9.7 billion solar masses, and that a black hole of comparable or greater mass is present in NGC 4889, the brightest galaxy in the Coma cluster (at a distance of 103 megaparsecs). These two black holes are significantly more massive than predicted by linearly extrapolating the widely used correlations between black-hole mass and the stellar velocity dispersion or bulge luminosity of the host galaxy. Although these correlations remain useful for predicting black-hole masses in less massive elliptical galaxies, our measurements suggest that different evolutionary processes influence the growth of the largest galaxies and their black holes.     

Rapid evolution of the most luminous galaxies during the first 900 million years

The first 900 million years (Myr) to redshift z approximately 6 (the first seven per cent of the age of the Universe) remains largely unexplored for the formation of galaxies. Large samples of galaxies have been found at z approximately 6 (refs 1-4) but detections at earlier times are uncertain and unreliable. It is not at all clear how galaxies built up from the first stars when the Universe was about 300 Myr old (z approximately 12-15) to z approximately 6, just 600 Myr later. Here we report the results of a search for galaxies at z approximately 7-8, about 700 Myr after the Big Bang, using the deepest near-infrared and optical images ever taken. Under conservative selection criteria we find only one candidate galaxy at z approximately 7-8, where ten would be expected if there were no evolution in the galaxy population between z approximately 7-8 and z approximately 6. Using less conservative criteria, there are four candidates, where 17 would be expected with no evolution. This demonstrates that very luminous galaxies are quite rare 700 Myr after the Big Bang. The simplest explanation is that the Universe is just too young to have built up many luminous galaxies at z approximately 7-8 by the hierarchical merging of small galaxies.