Recent Postings from Special Topics

An ultraluminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30

An ultraluminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
Xue-Bing Wu, Feige Wang, Xiaohui Fan, Weimin Yi, Wenwen Zuo, Fuyan Bian, Linhua Jiang, Ian D. McGreer, Ran Wang, Jinyi Yang, Qian Yang, David Thompson & Yuri Beletsky

Nature 518, 512–515 (26 February 2015)

Editor’s summary:
Cosmic redshifts of between 6 and 7 represent a time when the intergalactic medium was in transition from a neutral state to being completely ionized. Here Xue-Bing Wu et al. report the discovery of an ultraluminous quasar at redshift z = 6.30 that has optical and near-infrared luminosity several times greater than previously known quasars at redshifts beyond 6. Based on near-infrared spectral data, the authors estimate a mass of approximately twelve-billion solar-masses for the associated black hole, consistent with the thirteen-billion solar masses derived by assuming an Eddington-limited accretion rate, where the force of radiation acting outwards and the gravitational force acting inwards are in balance. As the most luminous quasar known to date at z = 6, this object will be a useful resource for the study of galaxy formation around massive black holes at the end of the epoch of cosmic reionization.

A higher-than-predicted measurement of iron opacity at solar interior temperatures

Nearly a century ago it was recognized1 that radiation absorption by stellar matter controls the internal temperature profiles within stars. Laboratory opacity measurements, however, have never been performed at stellar interior conditions, introducing uncertainties in stellar models2345. A particular problem arose23678 when refined photosphere spectral analysis910 led to reductions of 30–50 per cent in the inferred amounts of carbon, nitrogen and oxygen in the Sun. Standard solar models11 using the revised element abundances disagree with helioseismic observations that determine the internal solar structure using acoustic oscillations. This could be resolved if the true mean opacity for the solar interior matter were roughly 15 per cent higher than predicted23678, because increased opacity compensates for the decreased element abundances. Iron accounts for a quarter of the total opacity212 at the solar radiation/convection zone boundary. Here we report measurements of wavelength-resolved iron opacity at electron temperatures of 1.9–2.3 million kelvin and electron densities of (0.7–4.0) × 1022 per cubic centimetre, conditions very similar to those in the solar region that affects the discrepancy the most: the radiation/convection zone boundary. The measured wavelength-dependent opacity is 30–400 per cent higher than predicted. This represents roughly half the change in the mean opacity needed to resolve the solar discrepancy, even though iron is only one of many elements that contribute to opacity.


2014 Update of the Discoveries of Nuclides

M. Thoennessen

The 2014 update of the discovery of nuclide project is presented. Only six new nuclides were observed for the first time in 2014 while the assignments of seventeen other nuclides were revised. In addition, for another fourteen nuclides the laboratories where they were discovered were reassigned.

Systematic inequality and hierarchy in faculty hiring networks

The faculty job market plays a fundamental role in shaping research priorities, educational outcomes, and career trajectories among scientists and institutions. However, a quantitative understanding of faculty hiring as a system is lacking. Using a simple technique to extract the institutional prestige ranking that best explains an observed faculty hiring network—who hires whose graduates as faculty—we present and analyze comprehensive placement data on nearly 19,000 regular faculty in three disparate disciplines. Across disciplines, we find that faculty hiring follows a common and steeply hierarchical structure that reflects profound social inequality. Furthermore, doctoral prestige alone better predicts ultimate placement than a U.S. News & World Report rank, women generally place worse than men, and increased institutional prestige leads to increased faculty production, better faculty placement, and a more influential position within the discipline. These results advance our ability to quantify the influence of prestige in academia and shed new light on the academic system.


The formation of a quadruple star system with wide separation

“The formation of a quadruple star system with wide separation”, published in Nature, Feb 12th:

Detection of galaxy assembly bias

The double-degenerate, super-Chandrasekhar nucleus of the planetary nebula Henize 2–428


“The planetary nebula (PN) stage is the ultimate fate of stars with mass 1 to 8 solar masses (M⊙). The origin of their complex morphologies is poorly understood1 , although several mechanisms involving binary interaction have been proposed 2,3 . In close binary systems, the orbital separation is short enough for the primary star to overfill its Roche lobe as it expands during the Asymptotic Giant Branch (AGB) phase. The excess material ends up forming a common-envelope (CE) surrounding both stars. Drag forces would then result in the envelope being ejected into a bipolar PN whose equator is coincident with the orbital plane of the system. Systems in which both stars have ejected their envelopes and evolve towards the white dwarf (WD) stage are called double-degenerates. Here we report the case of Henize 2-428, the first double-degenerate binary which has, without any ambiguity, a total mass above the Chandrasekhar limit. According to its short orbital period (4.2 hours) and total mass (∼1.8 M⊙), the system should merge in 700 million years, triggering a Type Ia supernova (SN Ia) event. This finding supports the double-degenerate, super-Chandrasekhar evolutionary channel for the formation of SNe Ia4 .”

Planck 2015 Results

A Joint Analysis of BICEP2/Keck Array and Planck Data

We report the results of a joint analysis of data from BICEP2/Keck Array and Planck. BICEP2 and Keck Array have observed the same approximately 400 deg2 patch of sky centered on RA 0h, Dec. −57.5°. The combined maps reach a depth of 57 nK deg in Stokes Q and U in a band centered at 150 GHz. Planck has observed the full sky in polarization at seven frequencies from 30 to 353 GHz, but much less deeply in any given region (1.2 µK deg in Q and U at 143 GHz). We detect 150×353 cross-correlation in B-modes at high significance. We fit the single- and cross frequency power spectra at frequencies above 150 GHz to a lensed-ΛCDM model that includes dust and a possible contribution from inflationary gravitational waves (as parameterized by the tensor-to-scalar ratio r). We probe various model variations and extensions, including adding a synchrotron component in combination with lower frequency data, and find that these make little difference to the r constraint. Finally we present an alternative analysis which is similar to a map-based cleaning of the dust contribution, and show that this gives similar constraints. The final result is expressed as a likelihood curve for r, and yields an upper limit r0.05 < 0.12 at 95% confidence. Marginalizing over dust and r, lensing B-modes are detected at 7.0 σ significance.



Press releases:

BICEP2+Planck Press release

Bottom line:

No evidence for primordial gravitational waves:

(mars 2013)
(février 2014)
(décembre 2014)
(janvier 2015)
r < 0.11 r = 0.16-0.20 r < 0.11 r < 0.13

Wind-driven circulation in Titan's seas

A higher-than-predicted measurement of iron opacity at solar interior temperatures

“A higher-than-predicted measurement of iron opacity at solar interior temperatures” by Bailey et al.

Nearly a century ago it was recognized1 that radiation absorption by stellar matter controls the internal temperature profiles within stars. Laboratory opacity measurements, however, have never been performed at stellar interior conditions, introducing uncertainties in stellar models2, 3, 4, 5. A particular problem arose2, 3, 6, 7, 8 when refined photosphere spectral analysis9, 10 led to reductions of 30–50 per cent in the inferred amounts of carbon, nitrogen and oxygen in the Sun. Standard solar models11 using the revised element abundances disagree with helioseismic observations that determine the internal solar structure using acoustic oscillations. This could be resolved if the true mean opacity for the solar interior matter were roughly 15 per cent higher than predicted2, 3, 6, 7, 8, because increased opacity compensates for the decreased element abundances. Iron accounts for a quarter of the total opacity2, 12 at the solar radiation/convection zone boundary. Here we report measurements of wavelength-resolved iron opacity at electron temperatures of 1.9–2.3 million kelvin and electron densities of (0.7–4.0) × 1022 per cubic centimetre, conditions very similar to those in the solar region that affects the discrepancy the most: the radiation/convection zone boundary. The measured wavelength-dependent opacity is 30–400 per cent higher than predicted. This represents roughly half the change in the mean opacity needed to resolve the solar discrepancy, even though iron is only one of many elements that contribute to opacity.

Planck 2014 results

Planck Press Release Dec 1 2014 (in French, en francais)

Planck press release (now with polarization!) includes two more technical pages (both in French):

Dark Matter and (if I read the bottom panel correctly) no B-Modes and lensing B-modes

and Neutrinos (looks like N_eff ~ 3):

Solar nebula magnetic fields recorded in the Semarkona meteorite

PDF, Supplementary PDF


Magnetic fields are proposed to have played a critical role in some of the most enigmatic processes of planetary formation by mediating the rapid accretion of disk material onto the central star and the formation of the first solids. However, there have been no experimental constraints on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite were magnetized in a nebular field of 54 ± 21 μT. This intensity supports chondrule formation by nebular shocks or planetesimal collisions rather than by electric currents, the x-wind, or other mechanisms near the sun. This implies that background magnetic fields in the terrestrial planet-forming region were likely 5-54 μT, which is sufficient to account for measured rates of mass and angular momentum transport in protoplanetary disks.

Unusual Activity in the Atmosphere of Uranus in 2014

Announced at DPS. No paper posted yet. UCB Press release:



Uranus continues to evolve as it progresses through the post-equinoctial season. Images taken on 5 and 6 August 2014 at the 10-m Keck 2 telescope show significant atmospheric activity in the planet’s northern (currently sun-facing) hemisphere. Although Keck’s adaptive optics system was underperforming (resulting in artifacts and some blurring), many discrete features were visible on the planet at H (1.6 microns) and K’ (2.2 microns). Many of these features reached altitudes above the 1-bar level, as evidenced by their detection at K’. One feature breaks the record as the brightest ever detected or Uranus at K’, producing 30% of the total light reflected by the planet in that filter, compared to 12% for the previous record in 2005 (Sromovsky et al., Icarus 192, 558-575, 2007). The 2014 feature’s morphology was similar at both K’ and H, suggestive of an underlying vortex (e.g., Hammel et al., Icarus 201, 257-271, 2009). However, the feature’s brightest region in K’ is not particularly bright in H; i.e, although it is relatively high in altitude, it does not have a high optical depth. The total light fraction at H is only 2-3%, compared to the 4-5% found for the 2005 feature. Thus, its visible-wavelength contrast may be low; this could explain why there have been no amateur follow-up detections as of this writing. The new images also reveal development of a long-expected north polar haze as well as polar cloud features. Interestingly, some discrete polar features were visible through the polar haze. This may indicate that the northern polar haze is not yet at an optical depth comparable to that of the fully-formed southern polar haze seen in pre-equinoctial years. Acknowledgements: the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among Caltech, University of California and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation. The authors acknowledge the significant cultural role of Mauna Kea’s summit, and extend thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests.

Punga Mare Waves

Cassini/VIMS observes rough surfaces on Titan’s Punga Mare in specular reflection

The Science of the Movie "Interstellar"

There’s been quite a bit of chatter on the internet regarding the validity of some of the science presented in the movie. It’s not often that this little corner of astrophysics gets such a public presentation, so I figured it might be interesting for astrophysics institutions to discuss the movie for a few minutes around the water cooler.

Birth of Planets Revealed in Astonishing Detail in ALMA's 'Best Image Ever'

[NRAO Press Release]

Astronomers have captured the best image ever of planet formation around an infant star as part of the testing and verification process for the Atacama Large Millimeter/submillimeter Array’s (ALMA) new high-resolution capabilities.

This revolutionary new image reveals in astonishing detail the planet-forming disk surrounding HL Tau, a Sun-like star located approximately 450 light-years from Earth in the constellation Taurus.

ALMA uncovered never-before-seen features in this system, including multiple concentric rings separated by clearly defined gaps. These structures suggest that planet formation is already well underway around this remarkably young star… [abridged]


See also Phil Plait’s blog post:

Pulsations as a driver for LBV variability

Pulsations as a driver for LBV variability
Lovekin, C. C. ; Guzik, J. A.
Monthly Notices of the Royal Astronomical Society, Volume 445, Issue 2, p.1766-1773
Published in Dec 2014

Among the most spectacular variable stars are the luminous blue variables (LBVs), which can show three types of variability. The LBV phase of evolution is poorly understood, and the driving mechanisms for the variability are not known. The most common type of variability, the S Dor instability, occurs on time-scales of tens of years. During an S Dor outburst, the visual magnitude of the star increases, while the bolometric magnitude stays approximately constant. In this work, we investigate pulsation as a possible trigger for the S Dor-type outbursts. We calculate the pulsations of envelope models using a non-linear hydrodynamic code including a time-dependent convection treatment. We initialize the pulsation in the hydrodynamic model based on linear non-adiabatic calculations. Pulsation properties for a full grid of models from 20 to 85 M were calculated, and in this paper, we focus on the few models that show either long-period pulsations or outburst-like behaviour, with photospheric radial velocities reaching 70-80 km s-1. At the present time, our models cannot follow mass-loss, so once the outburst event begins, our simulations are terminated. Our results show that pulsations alone are not able to drive enough surface expansion to eject the outer layers. However, the outbursts and long-period pulsations discussed here produce large variations in effective temperature and luminosity, which are expected to produce large variations in the radiatively driven mass-loss rates.

An ultraluminous X-ray source powered by an accreting neutron star

The majority of ultraluminous X-ray sources are point sources that are spatially offset from the nuclei of nearby galaxies and whose X-ray luminosities exceed the theoretical maximum for spherical infall (the Eddington limit) onto stellar-mass black holes12. Their X-ray luminosities in the 0.5–10 kiloelectronvolt energy band range from 1039 to 1041 ergs per second3. Because higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit, theoretical models have focused on black hole rather than neutron star systems12. The most challenging sources to explain are those at the luminous end of the range (more than 1040 ergs per second), which require black hole masses of 50–100 times the solar value or significant departures from the standard thin disk accretion that powers bright Galactic X-ray binaries, or both. Here we report broadband X-ray observations of the nuclear region of the galaxy M82 that reveal pulsations with an average period of 1.37 seconds and a 2.5-day sinusoidal modulation. The pulsations result from the rotation of a magnetized neutron star, and the modulation arises from its binary orbit. The pulsed flux alone corresponds to an X-ray luminosity in the 3–30 kiloelectronvolt range of 4.9 × 1039 ergs per second. The pulsating source is spatially coincident with a variable source4 that can reach an X-ray luminosity in the 0.3–10 kiloelectronvolt range of 1.8 × 1040 ergs per second1. This association implies a luminosity of about 100 times the Eddington limit for a 1.4-solar-mass object, or more than ten times brighter than any known accreting pulsar. This implies that neutron stars may not be rare in the ultraluminous X-ray population, and it challenges physical models for the accretion of matter onto magnetized compact objects.

Data Smashing

Data Smashing

Ishanu Chattopadhyay, Hod Lipson
ArXiv: 1401.0742

Investigation of the underlying physics or biology from empirical data requires a quantifiable notion of similarity – when do two observed data sets indicate nearly identical generating processes, and when they do not. The discriminating characteristics to look for in data is often determined by heuristics designed by experts, e.g., distinct shapes of “folded” lightcurves may be used as “features” to classify variable stars, while determination of pathological brain states might require a Fourier analysis of brainwave activity. Finding good features is non-trivial. Here, we propose a universal solution to this problem: [...] In our examples, the data smashing principle, without access to any domain knowledge, meets or exceeds the performance of specialized algorithms tuned by domain experts.

Water vapor absorption in the clear atmosphere of a Neptune-sized exoplanet

J. Fraine, D. Deming, B. Benneke, H. Knutson, A. Jordan, N. Espinoza, N. Madhusudhan, A. Wilkins & K. Todorov

Transmission spectroscopy has so far detected atomic and molecular absorption in Jupiter-sized exoplanets, but intense efforts to measure molecular absorption in the atmospheres of smaller (Neptune-sized) planets during transits have revealed only featureless spectra1, 2, 3, 4. From this it was concluded that the majority of small, warm planets evolve to sustain atmospheres with high mean molecular weights (little hydrogen), opaque clouds or scattering hazes, reducing our ability to observe the composition of these atmospheres1, 2, 3, 4, 5. Here we report observations of the transmission spectrum of the exoplanet HAT-P-11b (which has a radius about four times that of Earth) from the optical wavelength range to the infrared. We detected water vapour absorption at a wavelength of 1.4 micrometres. The amplitude of the water absorption (approximately 250 parts per million) indicates that the planetary atmosphere is predominantly clear down to an altitude corresponding to about 1 millibar, and sufficiently rich in hydrogen to have a large scale height (over which the atmospheric pressure varies by a factor of e). The spectrum is indicative of a planetary atmosphere in which the abundance of heavy elements is no greater than about 700 times the solar value. This is in good agreement with the core-accretion theory of planet formation, in which a gas giant planet acquires its atmosphere by accreting hydrogen-rich gas directly from the protoplanetary nebula onto a large rocky or icy core6.

Use “Dead Weight” on Mars Spacecraft to Advance Science and Technology

NASA is looking for creative yet practical ideas to find a dual purpose for Balance mass (“dead weight”) that is jettisoned from Mars landers like the Mars Science Laboratory (MSL) to balance the spacecraft during entry and landing. Payloads replacing Balance mass should perform some type of scientific or technological function adding to our knowledge base while closely matching the volume and weight characteristics of the original Balance mass. Ideas are welcomed from all disciplines. This Challenge requires only a written proposal.

Cash awards up to $1 million.

AMS-02 Press Release on CR Electrons and Positrons

CERN press release including updated positron fraction results

High Statistics Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–500 GeV with the Alpha Magnetic Spectrometer on the International Space Station

Phys. Rev. Lett. 113, 121101 – Published 18 September 2014
L. Accardo et al. (AMS Collaboration)

Electron and Positron Fluxes in Primary Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the International Space Station

Phys. Rev. Lett. 113, 121102 – Published 18 September 2014
M. Aguilar et al. (AMS Collaboration)

Neutrinos from the primary proton–proton fusion process in the Sun

Borexino Collaboration

In the core of the Sun, energy is released through sequences of nuclear reactions that convert hydrogen into helium. The primary reaction is thought to be the fusion of two protons with the emission of a low-energy neutrino. These so-called pp neutrinos constitute nearly the entirety of the solar neutrino flux, vastly outnumbering those emitted in the reactions that follow. Although solar neutrinos from secondary processes have been observed, proving the nuclear origin of the Sun’s energy and contributing to the discovery of neutrino oscillations, those from proton–proton fusion have hitherto eluded direct detection. Here we report spectral observations of pp neutrinos, demonstrating that about 99 per cent of the power of the Sun, 3.84 × 1033 ergs per second, is generated by the proton–proton fusion process.

Online networks and subjective well-being

A chemical signature of first-generation very massive stars

by W. Aoki, N. Tominaga, T. C. Beers, S. Honda, Y. S. Lee

Numerical simulations of structure formation in the early universe predict the formation of some fraction of stars with several hundred solar masses. No clear evidence of supernovae from such very massive stars has, however, yet been found in the chemical compositions of Milky Way stars. We report on an analysis of a very metal-poor star SDSS J001820.5–093939.2, which possesses elemental-abundance ratios that differ significantly from any previously known star. This star exhibits low [α-element Fe] ratios and large contrasts between the abundances of odd and even element pairs, such as scandium/titanium and cobalt/nickel. Such features have been predicted by nucleosynthesis models for supernovae of stars more than 140 times as massive as the Sun, suggesting that the mass distribution of first-generation stars might extend to 100 solar masses or larger.

A 400-solar-mass black hole in the galaxy M82

by Dheeraj R. Pasham, Tod E. Strohmayer & Richard F. Mushotzky

M82 X-1, the brightest X-ray source in the galaxy M82, has been thought to be an intermediate-mass black hole (100 to 10,000 solar masses) because of its extremely high luminosity and variability characteristics1, 2, 3, 4, 5, 6, although some models suggest that its mass may be only about 20 solar masses3, 7. The previous mass estimates were based on scaling relations that use low-frequency characteristic timescales which have large intrinsic uncertainties8, 9. For stellar-mass black holes, we know that the high-frequency quasi-periodic oscillations (100–450 hertz) in the X-ray emission that occur in a 3:2 frequency ratio are stable and scale in frequency inversely with black hole mass with a reasonably small dispersion10, 11, 12, 13, 14, 15. The discovery of such stable oscillations thus potentially offers an alternative and less ambiguous means of mass determination for intermediate-mass black holes, but has hitherto not been realized. Here we report stable, twin-peak (3:2 frequency ratio) X-ray quasi-periodic oscillations from M82 X-1 at frequencies of 3.32 ± 0.06 hertz and 5.07 ± 0.06 hertz. Assuming that we can extrapolate the inverse-mass scaling that holds for stellar-mass black holes, we estimate the black hole mass of M82 X-1 to be 428 ± 105 solar masses. In addition, we can estimate the mass using the relativistic precession model, from which we get a value of 415 ± 63 solar masses.

Spectral Calibration in the Mid-Infrared: Challenges and Solutions

Spectral Calibration in the Mid-Infrared: Challenges and Solutions

G.C. Sloan (Cornell), T.L. Herter (Cornell), V. Charmandaris (Univ. of Crete), K. Sheth (NRAO), M. Burgdorf (HE Space Operations, Bremen), and J.R. Houck (Cornell)

2014, AJ, in press.

Full manuscript available locally (PDF).

The 53 IRS spectra described in this paper are available on this website.

We present spectra obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope of 33 K giants and 20 A dwarfs to assess their suitability as spectrophotometric standard stars. The K giants confirm previous findings that the strength of the SiO absorption band at 8 um increases for both later optical spectral classes and redder (B-V)0 colors, but with considerable scatter. For K giants, the synthetic spectra underpredict the strengths of the molecular bands from SiO and OH. For these reasons, the assumed true spectra for K giants should be based on neither the assumption that molecular band strengths in the infrared can be predicted accurately from optical spectral class or color nor synthetric spectra. The OH bands in K giants grow stronger with cooler stellar temperatures, and they are stronger than predicted by synthetic spectra. As a group, A dwarfs are better behaved and more predictable than the K giants, but they are more likely to show red excesses from debris disks. No suitable A dwarfs were located in parts of the sky continuously observable from Spitzer, and with previous means of estimating the true spectra of K giants ruled out, it was necessary to use models of A dwarfs to calibrate spectra of K giants from observed spectral ratios of the two groups and then use the calibrated K giants as standards for the full database of infrared spectra from Spitzer. We also describe a lingering artifact that affects the spectra of faint blue sources at 24 µm.


Velocity anti-correlation of diametrically opposed galaxy satellites in the low-redshift Universe

Neil G. Ibata, Rodrigo A. Ibata, Benoit Famaey & Geraint F. Lewis

Recent work has shown that the Milky Way and the Andromeda galaxies both possess the unexpected property that their dwarf satellite galaxies are aligned in thin and kinematically coherent planar structures. It is interesting to evaluate the incidence of such planar structures in the larger galactic population, because the Local Group may not be a representative environment. Here we report measurements of the velocities of pairs of diametrically opposed satellite galaxies. In the local Universe (redshift z < 0.05), we find that satellite pairs out to a distance of 150 kiloparsecs from the galactic centre are preferentially anti-correlated in their velocities (99.994 per cent confidence level), and that the distribution of galaxies in the larger-scale environment (out to distances of about 2 megaparsecs) is strongly clumped along the axis joining the inner satellite pair (>7σ confidence). This may indicate that planes of co-rotating satellites, similar to those seen around the Andromeda galaxy, are ubiquitous, and their coherent motion suggests that they represent a substantial repository of angular momentum on scales of about 100 kiloparsecs.

Published BICEP2 Results

Slightly revised from

Just one proposal per year, please, NSF tells astronomers

Later this summer, NSF’s astronomy division intends to announce a new policy that will “strongly encourage” scientists to submit just a single proposal for each annual funding cycle. The voluntary cap is designed to boost success rates, which would please applicants. It’s also meant to ease the workload and frustration levels of peer reviewers poring over proposals that they know have little chance of getting funded.

“It’s a first step,” says James Ulvestad, director of NSF’s astronomy division. If it doesn’t achieve the desired effect, he adds, “we may have to make it mandatory in 2016 for the sake of reviewers’ sanity.”

Science 20 June 2014:
Vol. 344 no. 6190 p. 1328
DOI: 10.1126/science.344.6190.1328

A Wolf-Rayet-like progenitor of SN 2013cu from spectral observations of a stellar wind

Gal-Yam et al. 2014

The explosive fate of massive Wolf-Rayet stars (WRSs) is a key open question in stellar physics. An appealing option is that hydrogen-deficient WRSs are the progenitors of some hydrogen-poor supernova explosions of types IIb, Ib and Ic (ref. 2). A blue object, having luminosity and colours consistent with those of some WRSs, has recently been identified in pre-explosion images at the location of a supernova of type Ib (ref. 3), but has not yet been conclusively determined to have been the progenitor. Similar work has so far only resulted in non-detections. Comparison of early photometric observations of type Ic supernovae with theoretical models suggests that the progenitor stars had radii of less than 1012 centimetres, as expected for some WRSs. The signature of WRSs, their emission line spectra, cannot be probed by such studies. Here we report the detection of strong emission lines in a spectrum of type IIb supernova 2013cu (iPTF13ast) obtained approximately 15.5 hours after explosion (by `flash spectroscopy’, which captures the effects of the supernova explosion shock breakout flash on material surrounding the progenitor star). We identify Wolf-Rayet-like wind signatures, suggesting a progenitor of the WN(h) subclass (those WRSs with winds dominated by helium and nitrogen, with traces of hydrogen). The extent of this dense wind may indicate increased mass loss from the progenitor shortly before its explosion, consistent with recent theoretical predictions.

The Open Journal of Astrophysics

Discussion of

The different neighbours around Type-1 and Type-2 active galactic nuclei

Beatriz Villaroel and Andreas J. Korn, 2014, Nature Physics, “The different neighbours around Type-1 and Type-2 active galactic nuclei”

News and Views
Martin Gaskell, “Astronomy: Unifying active galactic nuclei”


Abstract: One of the most intriguing open issues in galaxy evolution is the structure and evolution of active galactic nuclei (AGN) that emit intense light believed to come from an accretion disk near a super massive black hole12. To understand the zoo of different AGN classes, it has been suggested that all AGN are the same type of object viewed from different angles3. This model—called AGN unification—has been successful in predicting, for example, the existence of hidden broad optical lines in the spectrum of many narrow-line AGN. But this model is not unchallenged4 and it is debatable whether more than viewing angle separates the so-called Type-1 and Type-2 AGN. Here we report the first large-scale study that finds strong differences in the galaxy neighbours to Type-1 and Type-2 AGN with data from the Sloan Digital Sky Survey (SDSS; ref. 5) Data Release 7 (DR7; ref. 6) and Galaxy Zoo78. We find strong differences in the colour and AGN activity of the neighbours to Type-1 and Type-2 AGN and in how the fraction of AGN residing in spiral hosts changes depending on the presence or not of a neighbour. These findings suggest that an evolutionary link between the two major AGN types might exist.


Properties of galaxies reproduced by a hydrodynamic simulation

by M. Vogelsberger, S. Genel, V. Springel, P. Torrey, D. Sijacki, D. Xu, G. Snyder, S. Bird, D. Nelson & L. Hernquist

Previous simulations of the growth of cosmic structures have broadly reproduced the ‘cosmic web’ of galaxies that we see in the Universe, but failed to create a mixed population of elliptical and spiral galaxies, because of numerical in- accuracies and incomplete physical models. Moreover, they were unable to track the small-scale evolution of gas and stars to the present epoch within a representative portion of the Universe. Here we report a simulation that starts 12 million years after the Big Bang, and traces 13 billion years of cosmic evolution with 12 billion resolution elements in a cube of 106.5 megaparsecs a side. It yields a reasonable population of ellipticals and spirals, reproduces the observed distribution of galaxies in clusters and characteristics of hydrogen on large scales, and at the same time matches the ‘metal’ and hydrogen content of galaxies on small scales.


Tegmark Inflation Chapter

Guest post by Max Tegmark on Sean Carroll’s blog Preposterous Universe about inflation.

Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun

Abstract: Through a previous analysis of multi-epoch astrometry from the Wide-field Infrared Survey Explorer (WISE), I identified WISE J085510.83–071442.5 as a new high proper motion object. By combining astrometry from WISE and the Spitzer Space Telescope, I have measured a proper motion of 8.1 ± 0.1” yr–1 and a parallax of 0.454 ± 0.045” ($2.20^{+0.24}_{-0.20}$ pc) for WISE J085510.83–071442.5, giving it the third highest proper motion and the fourth largest parallax of any known star or brown dwarf. It is also the coldest known brown dwarf based on its absolute magnitude at 4.5 μm and its color in [3.6]-[4.5]. By comparing M 4.5 with the values predicted by theoretical evolutionary models, I estimate an effective temperature of 225-260 K and a mass of 3-10 M Jup for the age range of 1-10 Gyr that encompasses most nearby stars.


An Earth-Sized Planet in the Habitable Zone of a Cool Star

Quintana et al., Science, 18 April 2014

The quest for Earth-like planets is a major focus of current exoplanet research. Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces. We present the detection of Kepler-186f, a 1.11 ± 0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47 ± 0.05 solar-radius star. The intensity and spectrum of the star’s radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form.

The bathymetry of a Titan sea

A Necro-Biological Explanation for the Fermi Paradox


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