Explore the vast range of titles available.

An early look at a galactic cluster A 'protocluster' of massive galaxies at a redshift z = 5.3, dating to only a billion years after the Big Bang, has been discovered in data from the Cosmological Evolution Survey (COSMOS), a project combining the power of the Hubble Space Telescope and ground-based telescopes on 2 square degrees of sky in the constellation Sextans. The protocluster occupies an overdense region more than 13 megaparsecs (40 million light years) across, rich in molecular gas and young stars. Its properties match the predictions of galaxy formation simulations, suggesting that the protocluster will evolve into a massive galaxy cluster typical of those seen at lower redshifts. Massive clusters of galaxies have been found as early as 3.9 billion years after the Big Bang. Cosmological simulations predict that these systems should descend from 'protoclusters' — early overdensities of massive galaxies that merge hierarchically to form a cluster. Observational evidence for this picture, however, is sparse because high-redshift protoclusters are rare and difficult to observe. Here, a protocluster region 1 billion years ( z = 5.3) after the Big Bang is reported. This cluster extends over >13 megaparsecs, contains a luminous quasar as well as a system rich in molecular gas. A lower limit of >4 × 10 11 solar masses of dark and luminous matter in this region is placed, consistent with that expected from cosmological simulations. Massive clusters of galaxies have been found that date from as early as 3.9 billion years 1 (3.9 Gyr; z = 1.62) after the Big Bang, containing stars that formed at even earlier epochs 2 , 3 . 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 4 , 5 . 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 4 , 5 , 6 . Observational evidence for this picture, however, is sparse because high-redshift protoclusters are rare and difficult to observe 6 , 7 . 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 8 . 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 4 , 5 , 7 .

L-line route to black holes The emission line arising from a transition of an electron from the iron K shell to the ground state (the K line) is prominent in the reflection spectrum of the hard X-ray continuum irradiating dense accreting matter around a black hole. The corresponding iron L-line emission should be detectable when iron abundance is high. That's the theory, and now broad iron L-line emission has been observed, together with the broad K line in the narrow-line Seyfert galaxy 1H0707. There is a reverberation lag of about 30 s between the direct X-ray continuum and its reflection from matter falling into the hole, a timescale comparable to the light-crossing time of the innermost radii around a supermassive black hole. This discovery opens a window on events close to the black hole event horizon in these objects. Emission arising from a transition of an electron from the iron K shell to the ground state (the K line) is prominent in the reflection spectrum created by the hard X-ray continuum irradiating the dense accreting matter around a black hole. Here the presence of both iron K and L emission is reported in the spectrum of the active galaxy 1H 0707-495. There is a 'reverberation lag' with a timescale comparable to the light-crossing time of the innermost radii around a supermassive black hole. Since the 1995 discovery of the broad iron K-line emission from the Seyfert galaxy MCG–6-30-15 (ref. 1 ), broad iron K lines have been found in emission from several other Seyfert galaxies 2 , from accreting stellar-mass black holes 3 and even from accreting neutron stars 4 . The iron K line is prominent in the reflection spectrum 5 , 6 created by the hard-X-ray continuum irradiating dense accreting matter. Relativistic distortion 7 of the line makes it sensitive to the strong gravity and spin of the black hole 8 . The accompanying iron L-line emission should be detectable when the iron abundance is high. Here we report the presence of both iron K and iron L emission in the spectrum of the narrow-line Seyfert 1 galaxy 9 1H 0707-495. The bright iron L emission has enabled us to detect a reverberation lag of about 30 s between the direct X-ray continuum and its reflection from matter falling into the black hole. The observed reverberation timescale is comparable to the light-crossing time of the innermost radii around a supermassive black hole. The combination of spectral and timing data on 1H 0707-495 provides strong evidence that we are witnessing emission from matter within a gravitational radius, or a fraction of a light minute, from the event horizon of a rapidly spinning, massive black hole.

Observations at submillimetre and X-ray wavelengths show that rapid star formation was common in the host galaxies of active galactic nuclei when the Universe was 2–6 Gyr old, but that the most vigorous star formation is not observed around powerful black holes, thereby confirming a key prediction of models in which an active galactic nucleus expels the interstellar medium of its host galaxy. Star formation blocked by powerful black holes Radiation from active galactic nuclei (AGNs) outshines that produced by star formation at most wavelengths, but in the far-infrared to millimetre waveband AGNs emit comparatively little radiation in comparison with strongly star-forming galaxies. A combination of deep X-ray observations from the Chandra catalogue and submillimetre observations from the SPIRE instrument on the Herschel Space Observatory shows that rapid star formation was common in the host galaxies of AGNs when the Universe was between two billion and six billion years old, but that vigorous star formation is not seen around the more luminous black holes. This suppression of star formation in galaxies that host a powerful AGN is a key prediction of models in which the AGN expels the interstellar medium of its host galaxy when it becomes sufficiently powerful. The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge 1 results from the AGN quenching the surrounding star formation as it approaches its peak luminosity 2 , 3 , 4 . X-rays trace emission from AGN unambiguously 5 , whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths 6 . Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2–6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10 44 ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow 7 , 8 , 9 , expelling the interstellar medium of its host and transforming the galaxy’s properties in a brief period of cosmic time.

The relationship between radio jet and black hole Radio jets from active galactic nuclei, such as the nearby galaxy M87, are thought to be powered by the accretion of material into a supermassive black hole. The relative position of this 'central engine' and the bright radio core that marks the base of the jet remain the subject of much speculation. New observations of M87 at six frequencies have been used to determine the position of the radio core to an accuracy of ∼ 20 microarcseconds. The data reveal that the central engine is located close to the radio core, within a distance of 14–23 Schwarzschild radii at 43 GHz. Powerful radio jets from active galactic nuclei are thought to be powered by the accretion of material onto the supermassive black hole (the ‘central engine’) 1 , 2 . M87 is one of the closest examples of this phenomenon, and the structure of its jet has been probed on a scale of about 100 Schwarzschild radii ( R s , the radius of the event horizon) 3 . However, the location of the central black hole relative to the jet base (a bright compact radio ‘core’) remains elusive 4 , 5 . Observations of other jets indicate that the central engines are located about 10 4 –10 6 R s upstream from the radio core 6 , 7 , 8 , 9 . Here we report radio observations of M87 at six frequencies that allow us to achieve a positional accuracy of about 20 microarcseconds. As the jet base becomes more transparent at higher frequencies, the multifrequency position measurements of the radio core enable us to determine the upstream end of the jet. The data reveal that the central engine of M87 is located within 14–23 R s of the radio core at 43 GHz. This implies that the site of material infall onto the black hole and the eventual origin of the jet reside in the bright compact region seen on the image at 43 GHz.

Early galaxy revealed in Hubble data An ultra-deep search through the full Hubble Ultra Deep Field data set has uncovered a galaxy with a redshift of z ≈ 10, equivalent to an age of only 500 million years after the Big Bang. The data also provide strong constraints on the volume density of galaxies — and hence the star formation rate — at this time. The authors conclude that the star formation rate increased by a factor of ten in the time between z ≈ 10 and z ≈ 8, implying that this period in the heart of the reionization epoch was one in which galaxies were evolving very rapidly. Here, the full two-year Hubble Ultra Deep Field (HUDF09) data are used to conduct an ultra-deep search for z ≈10 galaxies in the heart of the reionization epoch, only 500 million years after the Big Bang. One possible z ≈10 galaxy candidate is found. It is also shown that regardless of source detections, the star formation rate density is much smaller (∼10%) at this time than it is just ∼200 million years later at z ≈8. The 100–200 million years prior to z ≈10 is clearly a crucial phase in the assembly of the earliest galaxies. 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 2 , 3 have yielded the first reliable detections of z  ≈ 8 galaxies 3 , 4 , 5 , 6 , 7 , 8 , 9 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.

Outflowing winds of multiphase plasma have been proposed to regulate the buildup of galaxies, but key aspects of these outflows have not been probed with observations. By using ultraviolet absorption spectroscopy, we show that \"warm-hot\" plasma at 10 5.5 kelvin contains 10 to 150 times more mass than the cold gas in a post-star burst galaxy wind. This wind extends to distances > 68 kiloparsecs, and at least some portion of it will escape. Moreover, the kinematical correlation of the cold and warm-hot phases indicates that the warm-hot plasma is related to the interaction of the cold matter with a hotter (unseen) phase at »10⁶ kelvin. Such multiphase winds can remove substantial masses and alter the evolution of post-star burst galaxies.

The cold dark matter model has become the leading theoretical picture for the formation of structure in the Universe. This model, together with the theory of cosmic inflation, makes a clear prediction for the initial conditions for structure formation and predicts that structures grow hierarchically through gravitational instability. Testing this model requires that the precise measurements delivered by galaxy surveys can be compared to robust and equally precise theoretical calculations. Here we present a simulation of the growth of dark matter structure using 2,160 3 particles, following them from redshift z = 127 to the present in a cube-shaped region 2.230 billion lightyears on a side. In postprocessing, we also follow the formation and evolution of the galaxies and quasars. We show that baryon-induced features in the initial conditions of the Universe are reflected in distorted form in the low-redshift galaxy distribution, an effect that can be used to constrain the nature of dark energy with future generations of observational surveys of galaxies. Evolution of the universe Computer simulations have been used to blend the giant snapshot of cosmic history provided by modern galaxy surveys into a coherent picture displaying the underlying physical processes of galaxy formation and evolution. The growth of 20 million galaxies in a huge cosmological volume was modelled and it proved possible to identify the unusual formation sites and eventual fate of the first bright quasars. It was shown that large surveys are likely to include features in the galaxy distribution that directly reflect physics in the early Universe and may clarify the nature of the mysterious dark energy driving its current accelerated expansion. The cover shows the distribution of dark matter in a slice of thickness 60 million lightyears through the simulated universe.

Active galactic nuclei: on the hour Although active galactic nuclei (AGNs) are thought — like quasars — to be scaled-up versions of binary black holes, quasiperiodic oscillations have proved elusive in the supermassive black holes found in AGNs. This is surprising, since these oscillations are generally so well defined in black holes. That anomaly has now been straightened out with the observation of X-ray emissions with a periodicity of about 1 hour in the bright active galaxy RE J1034+396. The X-ray modulation arises from the direct vicinity of the black hole. The study of this and similar phenomena should reveal more about accretion flows around black holes. Active galactic nuclei and quasars are thought to be scaled-up versions of Galactic black hole binaries, powered by accretion onto supermassive black holes with masses of 10 6 –10 9   , as opposed to the ∼10  in binaries (here is the solar mass). One example of the similarities between these two types of systems is the characteristic rapid X-ray variability seen from the accretion flow 1 . The power spectrum of this variability in black hole binaries consists of a broad noise with multiple quasi-periodic oscillations superimposed on it. Although the broad noise component has been observed in many active galactic nuclei 2 , 3 , there have hitherto been no significant detections of quasi-periodic oscillations 4 , 5 , 6 . Here we report the discovery of an ∼1-hour X-ray periodicity in a bright active galaxy, RE J1034+396. The signal is highly statistically significant (at the 5.6 σ level) and very coherent, with quality factor Q  > 16. The X-ray modulation arises from the direct vicinity of the black hole.

Galaxies, on the hole Most, if not all, galaxies in the Universe contain a central supermassive black hole. The accretion of matter onto such black holes is thought to power luminous quasars, but little is know about how black holes interact with galaxies. Using simulations of galaxy formation that follow star formation, black hole growth and the associated feedback processes, Di Matteo et al . now show that galactic mergers lead to strong nuclear gas inflows, fuelling powerful starbursts and rapid growth of central black holes. Black holes also have a crucial impact on the formation of galaxies themselves, with the properties of remnant galaxies closely related to final black hole masses. In the early Universe, while galaxies were still forming, black holes as massive as a billion solar masses powered quasars. Supermassive black holes are found at the centres of most galaxies today 1 , 2 , 3 , where their masses are related to the velocity dispersions of stars in their host galaxies and hence to the mass of the central bulge of the galaxy 4 , 5 . This suggests a link between the growth of the black holes and their host galaxies 6 , 7 , 8 , 9 , which has indeed been assumed for a number of years. But the origin of the observed relation between black hole mass and stellar velocity dispersion, and its connection with the evolution of galaxies, have remained unclear. Here we report simulations that simultaneously follow star formation and the growth of black holes during galaxy–galaxy collisions. We find that, in addition to generating a burst of star formation 10 , a merger leads to strong inflows that feed gas to the supermassive black hole and thereby power the quasar. The energy released by the quasar expels enough gas to quench both star formation and further black hole growth. This determines the lifetime of the quasar phase (approaching 100 million years) and explains the relationship between the black hole mass and the stellar velocity dispersion.

Bursting onto the scene The starburst in Henize 2-10, a relatively nearby blue compact dwarf galaxy, has attracted the attention of astronomers for decades, in part because of its prodigious rate of star formation — ten times that of the Large Magellanic Cloud. Now a study of Henize 2-10 at centimetre radio wavelengths and in the near-infrared reveals a compact radio source at its centre that is spatially coincident with a hard X-ray source. This points to the presence of an actively accreting massive black hole, but one not associated with a bulge, a nuclear star cluster or any other well-defined nucleus. This means that Henize 2-10 may reflect an early phase of black hole and galaxy evolution that has not been observed previously. Henize 2-10 is a nearby dwarf starburst galaxy that may be similar to galaxies in the infant Universe. It is reported that Henize 2-10 contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source, from which it is concluded that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. The results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and by implication so can their primordial counterparts. Supermassive black holes are now thought to lie at the heart of every giant galaxy with a spheroidal component, including our own Milky Way 1 , 2 . The birth and growth of the first ‘seed’ black holes in the earlier Universe, however, is observationally unconstrained 3 and we are only beginning to piece together a scenario for their subsequent evolution 4 . Here we report that the nearby dwarf starburst galaxy Henize 2-10 (refs 5 and 6 ) contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source. From these observations, we conclude that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. This nearby dwarf galaxy, simultaneously hosting a massive black hole and an extreme burst of star formation, is analogous in many ways to galaxies in the infant Universe during the early stages of black-hole growth and galaxy mass assembly. Our results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and that by implication so can their primordial counterparts. Moreover, the lack of a substantial spheroidal component in Henize 2-10 indicates that supermassive black-hole growth may precede the build-up of galaxy spheroids.