A galaxy at a redshift z = 6.96

When galaxy formation started in the history of the Universe remains unclear. Studies of the cosmic microwave background indicate that the Universe, after initial cooling (following the Big Bang), was reheated and reionized by hot stars in newborn galaxies at a redshift in the range 6 < z < 14 (ref. 1). Though several candidate galaxies at redshift z > 7 have been identified photometrically, galaxies with spectroscopically confirmed redshifts have been confined to z < 6.6 (refs 4-8). Here we report a spectroscopic redshift of z = 6.96 (corresponding to just 750 Myr after the Big Bang) for a galaxy whose spectrum clearly shows Lyman-alpha emission at 9,682 A, indicating active star formation at a rate of approximately 10M(o) yr(-1), where M(o) is the mass of the Sun. This demonstrates that galaxy formation was under way when the Universe was only approximately 6 per cent of its present age. The number density of galaxies at z approximately 7 seems to be only 18-36 per cent of the density at z = 6.6.     

Spectroscopic confirmation of a galaxy at redshift z = 8.6

Galaxies had their most significant impact on the Universe when they assembled their first generations of stars. Energetic photons emitted by young, massive stars in primeval galaxies ionized the intergalactic medium surrounding their host galaxies, cleared sightlines along which the light of the young galaxies could escape, and fundamentally altered the physical state of the intergalactic gas in the Universe continuously until the present day. Observations of the cosmic microwave background, and of galaxies and quasars at the highest redshifts, suggest that the Universe was reionized through a complex process that was completed about a billion years after the Big Bang, by redshift z?≈?6. Detecting ionizing Lyman-α photons from increasingly distant galaxies places important constraints on the timing, location and nature of the sources responsible for reionization. Here we report the detection of Lyα photons emitted less than 600?million years after the Big Bang. UDFy-38135539 (ref. 5) is at a redshift of z = 8.5549?±?0.0002, which is greater than those of the previously known most distant objects, at z = 8.2 (refs 6 and 7) and z = 6.96 (ref. 8). We find that this single source is unlikely to provide enough photons to ionize the volume necessary for the emission line to escape, requiring a significant contribution from other, probably fainter galaxies nearby.     

An optical spectrum of the afterglow of a gamma-ray burst at a redshift of z = 6.295

The prompt gamma-ray emission from gamma-ray bursts (GRBs) should be detectable out to distances of z > 10 (ref. 1), and should therefore provide an excellent probe of the evolution of cosmic star formation, reionization of the intergalactic medium, and the metal enrichment history of the Universe. Hitherto, the highest measured redshift for a GRB has been z = 4.50 (ref. 5). Here we report the optical spectrum of the afterglow of GRB 050904 obtained 3.4 days after the burst; the spectrum shows a clear continuum at the long-wavelength end of the spectrum with a sharp cut-off at around 9,000 A due to Lyman alpha absorption at z approximately 6.3 (with a damping wing). A system of absorption lines of heavy elements at z = 6.295 +/- 0.002 was also detected, yielding the precise measurement of the redshift. The Si ii fine-structure lines suggest a dense, metal-enriched environment around the progenitor of the GRB.     

A large neutral fraction of cosmic hydrogen a billion years after the Big Bang

The fraction of ionized hydrogen left over from the Big Bang provides evidence for the time of formation of the first stars and quasar black holes in the early Universe; such objects provide the high-energy photons necessary to ionize hydrogen. Spectra of the two most distant known quasars show nearly complete absorption of photons with wavelengths shorter than the Lyman alpha transition of neutral hydrogen, indicating that hydrogen in the intergalactic medium (IGM) had not been completely ionized at a redshift of z approximately 6.3, about one billion years after the Big Bang. Here we show that the IGM surrounding these quasars had a neutral hydrogen fraction of tens of per cent before the quasar activity started, much higher than the previous lower limits of approximately 0.1 per cent. Our results, when combined with the recent inference of a large cumulative optical depth to electron scattering after cosmological recombination therefore suggest the presence of a second peak in the mean ionization history of the Universe.     

A flat Universe from high-resolution maps of the cosmic microwave background radiation

The blackbody radiation left over from the Big Bang has been transformed by the expansion of the Universe into the nearly isotropic 2.73 K cosmic microwave background. Tiny inhomogeneities in the early Universe left their imprint on the microwave background in the form of small anisotropies in its temperature. These anisotropies contain information about basic cosmological parameters, particularly the total energy density and curvature of the Universe. Here we report the first images of resolved structure in the microwave background anisotropies over a significant part of the sky. Maps at four frequencies clearly distinguish the microwave background from foreground emission. We compute the angular power spectrum of the microwave background, and find a peak at Legendre multipole Ipeak = (197 +/- 6), with an amplitude delta T200 = (69 +/- 8) microK. This is consistent with that expected for cold dark matter models in a flat (euclidean) Universe, as favoured by standard inflationary models.     

Black hole growth in the early Universe is self-regulated and largely hidden from view

The formation of the first massive objects in the infant Universe remains impossible to observe directly and yet it sets the stage for the subsequent evolution of galaxies. Although some black holes with masses more than 10(9) times that of the Sun have been detected in luminous quasars less than one billion years after the Big Bang, these individual extreme objects have limited utility in constraining the channels of formation of the earliest black holes; this is because the initial conditions of black hole seed properties are quickly erased during the growth process. Here we report a measurement of the amount of black hole growth in galaxies at redshift z = 6-8 (0.95-0.7 billion years after the Big Bang), based on optimally stacked, archival X-ray observations. Our results imply that black holes grow in tandem with their host galaxies throughout cosmic history, starting from the earliest times. We find that most copiously accreting black holes at these epochs are buried in significant amounts of gas and dust that absorb most radiation except for the highest-energy X-rays. This suggests that black holes grew significantly more during these early bursts than was previously thought, but because of the obscuration of their ultraviolet emission they did not contribute to the re-ionization of the Universe.     

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.     

总星系局爆宇宙理论

大爆炸宇宙理论是一个非常成功的宇宙理论,它在经过古斯等人提出的暴涨理论修正后日趋完善。但即使这样也还存在几个难题无法解决：（1）欧洲普朗克望远镜揭示的宇宙背景辐射的不对称性;（2）宇宙中所有物质来源于大爆炸没有实验依据;（3）存在暴涨中宇宙膨胀的超光速问题。为了解释上述难题,本文提出了一种建立在大爆炸宇宙理论基础上的多宇宙模型：总星系局爆宇宙模型。该模型可以很好地解决上述难题,文中提出了检验理论模型新的实验方法,通过实验可以最终确认真实的宇宙到底更符合哪个模型。、     

The intense starburst HDF 850.1 in a galaxy overdensity at z ≈ 5.2 in the Hubble Deep Field

The Hubble Deep Field provides one of the deepest multiwavelength views of the distant Universe and has led to the detection of thousands of galaxies seen throughout cosmic time. An early map of the Hubble Deep Field at a wavelength of 850?micrometres, which is sensitive to dust emission powered by star formation, revealed the brightest source in the field, dubbed HDF?850.1 (ref. 2). For more than a decade, and despite significant efforts, no counterpart was found at shorter wavelengths, and it was not possible to determine its redshift, size or mass. Here we report a redshift of z = 5.183 for HDF?850.1, from a millimetre-wave molecular line scan. This places HDF?850.1 in a galaxy overdensity at z?≈?5.2, corresponding to a cosmic age of only 1.1?billion years after the Big Bang. This redshift is significantly higher than earlier estimates and higher than those of most of the hundreds of submillimetre-bright galaxies identified so far. The source has a star-formation rate of 850 solar masses per year and is spatially resolved on scales of 5 kiloparsecs, with an implied dynamical mass of about 1.3?×?10(11) solar masses, a significant fraction of which is present in the form of molecular gas. Despite our accurate determination of redshift and position, a counterpart emitting starlight remains elusive.     

Cosmic gamma-ray background from structure formation in the intergalactic medium

The Universe is filled with a diffuse background of gamma-ray radiation, the origin of which remains one of the unsolved puzzles of cosmology. Less than one-quarter of the gamma-ray flux can be attributed to unresolved discrete sources, such as active galactic nuclei; the remainder appears to constitute a truly diffuse background. Here we show that the shock waves induced by gravity in the gas of the intergalactic medium, during the formation of large-scale structures like filaments and sheets of galaxies, produce a population of highly relativistic electrons. These electrons scatter a small fraction of the cosmic microwave background photons in the local Universe up to gamma-ray energies, thereby providing the gamma-ray background. The predicted diffuse flux agrees with the observed background across more than four orders of magnitude in photon energy, and the model predicts that the gamma-ray background, though generated locally, is isotropic to better than five per cent on angular scales larger than a degree. Moreover, the agreement between the predicted and observed background fluxes implies a mean cosmological density of baryons that is consistent with Big Bang nucleosynthesis.     

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.     

宇宙模型的探究

介绍牛顿宇宙模型、奥伯斯佯谬、哈勃定律与大爆炸宇宙模型的认知历史;分析证明牛顿宇宙模型和奥伯斯佯谬无必然的因果关系;指出奥伯斯佯谬的隐含错误和大爆炸宇宙模型的证据尚不充分;提出零密度宇宙模型并证明该模型可以解析宇宙学红移现象.     

星光红移的碰撞解释

首先提出了星光光子与宇宙背景辐射光子碰上互作用引起了星光红移的假设,再用简化光子模型推导出了星光频率红移量与星体距离的正确关系式,将此结构与天文观测比较符合甚好,从而对宇宙中星光工移现象提出了另一种解释。     

A characteristic size of approximately 10 Mpc for the ionized bubbles at the end of cosmic reionization

The first galaxies to appear in the Universe at redshifts z > 20 created ionized bubbles in the intergalactic medium of neutral hydrogen left over from the Big Bang. The ionized bubbles grew with time, surrounding clusters of dwarf galaxies and eventually overlapped quickly throughout the Universe over a narrow redshift interval near z approximately 6. This event signalled the end of the reionization epoch when the Universe was a billion years old. Measuring the size distribution of the bubbles at their final overlap phase is a focus of forthcoming programmes to observe highly redshifted radio emission from atomic hydrogen. Here we show that the combined constraints of cosmic variance and light travel time imply an observed bubble size at the end of the overlap epoch of approximately 10 physical Mpc, and a scatter in the observed redshift of overlap along different lines-of-sight of approximately 0.15. This scatter is consistent with observational constraints from recent spectroscopic data on the farthest known quasars. This implies that future radio experiments should be tuned to a characteristic angular scale of 0.5 degrees and have a minimum frequency bandwidth of approximately 8 MHz for an optimal detection of 21-cm flux fluctuations near the end of reionization.     

Earth-mass dark-matter haloes as the first structures in the early Universe

The Universe was nearly smooth and homogeneous before a redshift of z = 100, about 20 million years after the Big Bang. After this epoch, the tiny fluctuations imprinted upon the matter distribution during the initial expansion began to collapse because of gravity. The properties of these fluctuations depend on the unknown nature of dark matter, the determination of which is one of the biggest challenges in present-day science. Here we report supercomputer simulations of the concordance cosmological model, which assumes neutralino dark matter (at present the preferred candidate), and find that the first objects to form are numerous Earth-mass dark-matter haloes about as large as the Solar System. They are stable against gravitational disruption, even within the central regions of the Milky Way. We expect over 10(15) to survive within the Galactic halo, with one passing through the Solar System every few thousand years. The nearest structures should be among the brightest sources of gamma-rays (from particle-particle annihilation).     

Gamma-ray bursts: huge explosion in the early Universe

Long gamma-ray bursts (GRBs) are bright flashes of high-energy photons that can last for tens of minutes; they are generally associated with galaxies that have a high rate of star formation and probably arise from the collapsing cores of massive stars, which produce highly relativistic jets (collapsar model). Here we describe gamma- and X-ray observations of the most distant GRB ever observed (GRB 050904): its redshift (z) of 6.29 means that this explosion happened 12.8 billion years ago, corresponding to a time when the Universe was just 890 million years old, close to the reionization era. This means that not only did stars form in this short period of time after the Big Bang, but also that enough time had elapsed for them to evolve and collapse into black holes.     

A massive protocluster of galaxies at a redshift of z ≈ 5.3

Massive clusters of galaxies have been found that date from as early as 3.9 billion years (3.9 Gyr; z = 1.62) after the Big Bang, containing stars that formed at even earlier epochs. Cosmological simulations using the current cold dark matter model predict that these systems should descend from 'protoclusters'-early overdensities of massive galaxies that merge hierarchically to form a cluster. These protocluster regions themselves are built up hierarchically and so are expected to contain extremely massive galaxies that can be observed as luminous quasars and starbursts. Observational evidence for this picture, however, is sparse because high-redshift protoclusters are rare and difficult to observe. Here we report a protocluster region that dates from 1 Gyr (z = 5.3) after the Big Bang. This cluster of massive galaxies extends over more than 13 megaparsecs and contains a luminous quasar as well as a system rich in molecular gas. These massive galaxies place a lower limit of more than 4 × 10(11) solar masses of dark and luminous matter in this region, consistent with that expected from cosmological simulations for the earliest galaxy clusters.     

The state of the Universe

The past 20 years have seen dramatic advances in cosmology, mostly driven by observations from new telescopes and detectors. These instruments have allowed astronomers to map out the large-scale structure of the Universe and probe the very early stages of its evolution. We seem to have established the basic parameters describing the behaviour of our expanding Universe, thereby putting cosmology on a firm empirical footing. But the emerging 'standard' model leaves many details of galaxy formation still to be worked out, and new ideas are emerging that challenge the theoretical framework on which the structure of the Big Bang is based. There is still a great deal left to explore in cosmology.     

从语用预设视角看言语幽默的产生—— 以《生活大爆炸》第十一季为例

以《生活大爆炸》第十一季为研究对象,从语用预设的视角,运用语用预设的共识性、合适性、可撤销性特征分析该剧日常会话,得出结论:违背语用预设的共识性和合适性,遵循语用预设的可撤销性对于日常会话中幽默的产生至关重要。     

暴涨宇宙与宇宙学常数问题

假设在宇宙暴涨时期,宇宙学"常数"不再是一个常数而是一个变化的量,并且由于它与暴涨场之间具有的相互作用,解决了宇宙学常数的精细调节问题.同时,这种相互作用也使得暴涨宇宙模型不仅能够预言大的张标比、正确的扰动谱,而且能预言大的谱指数跑动.此外,暴涨所需要的e-folding数也大到足够解决大爆炸宇宙学中的视界、平坦性等问题.