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We present a new reconstruction of the Event Horizon Telescope (EHT) image of the M87 black hole from the 2017 data set. We use PRIMO, a novel dictionary-learning-based algorithm that uses high-fidelity simulations of accreting black holes as a training set. By learning the correlations between the different regions of the space of interferometric data, this approach allows us to recover high-fidelity images even in the presence of sparse coverage and reach the nominal resolution of the EHT array. The black hole image comprises a thin bright ring with a diameter of 41.5 ± 0.6 μas and a fractional width that is at least a factor of 2 smaller than previously reported. This improvement has important implications for measuring the mass of the central black hole in M87 based on the EHT images.

The sparse interferometric coverage of the Event Horizon Telescope (EHT) poses a significant challenge for both reconstruction and model fitting of black hole images. PRIMO is a new principal components analysis-based algorithm for image reconstruction that uses the results of high-fidelity general relativistic, magnetohydrodynamic simulations of low-luminosity accretion flows as a training set. This allows the reconstruction of images that are consistent with the interferometric data and that live in the space of images that is spanned by the simulations. PRIMO follows Monte Carlo Markov Chains to fit a linear combination of principal components derived from an ensemble of simulated images to interferometric data. We show that PRIMO can efficiently and accurately reconstruct synthetic EHT data sets for several simulated images, even when the simulation parameters are significantly different from those of the image ensemble that was used to generate the principal components. The resulting reconstructions achieve resolution that is consistent with the performance of the array and do not introduce significant biases in image features such as the diameter of the ring of emission.

A new image-reconstruction algorithm, Principal-component Interferometric Modeling (PRIMO), applied to the interferometric data of the M87 black hole collected with the Event Horizon Telescope (EHT), resulted in an image that reached the native resolution of the telescope array. PRIMO is based on learning a compact set of image building blocks obtained from a large library of high-fidelity, physics-based simulations of black hole images. It uses these building blocks to fill the sparse Fourier coverage of the data that results from the small number of telescopes in the array. In this paper, we show that this approach is readily justified. Since the angular extent of the image of the black hole and of its inner accretion flow is finite, the Fourier space domain is heavily smoothed, with a correlation scale that is at most comparable to the sizes of the data gaps in the coverage of Fourier space with the EHT. Consequently, PRIMO or other machine learning algorithms can faithfully reconstruct the images without the need to generate information that is unconstrained by the data within the resolution of the array. We also address the completeness of the eigenimages and the compactness of the resulting representation. We show that PRIMO provides a compact set of eigenimages that have sufficient complexity to recreate a broad set of images well beyond those in the training set.

The Panchromatic Hubble Andromeda Southern Treasury (PHAST) is a large 195-orbit Hubble Space Telescope program imaging ∼0.45 deg2 of the southern half of M31's star-forming disk at optical and near-ultraviolet (NUV) wavelengths. The PHAST survey area extends the northern coverage of the Panchromatic Hubble Andromeda Treasury (PHAT) down to the southern half of M31, covering out to a radius of ∼13 kpc along the southern major axis and in total ∼two-thirds of M31's star-forming disk. This new legacy imaging yields stellar photometry of over 90 million resolved stars using the Advanced Camera for Surveys in the optical (F475W and F814W), and the Wide Field Camera 3 (WFC3) in the NUV (F275W and F336W). The photometry is derived using all overlapping exposures across all bands, and achieves a 50% completeness-limited depth of F475W ∼ 27.7 in the lowest surface density regions of the outer disk and F475W ∼ 26.0 in the most crowded, high surface brightness regions near M31's bulge. We provide extensive analysis of the data quality, including artificial star tests to quantify completeness, photometric uncertainties, and flux biases, all of which vary due to the background source density and the number of overlapping exposures. We also present seamless population maps of the entire M31 disk, which show relatively well-mixed distributions for stellar populations older than 1–2 Gyr, and highly structured distributions for younger populations. The combined PHAST + PHAT photometry catalog of ∼0.2 billion stars is the largest ever produced for equidistant sources and is available for public download by the community.

We demonstrate the use of an eigenbasis that is derived from principal component analysis (PCA) applied on an ensemble of random-noise images that have a “red” power spectrum; i.e., a spectrum that decreases smoothly from large to small spatial scales. The pattern of the resulting eigenbasis allows for the reconstruction of images with a broad range of image morphologies. In particular, we show that this general eigenbasis can be used to efficiently reconstruct images that resemble possible astronomical sources for interferometric observations, even though the images in the original ensemble used to generate the PCA basis are significantly different from the astronomical images. We further show that the efficiency and fidelity of the image reconstructions depends only weakly on the particular parameters of the red-noise power spectrum used to generate the ensemble of images.

We obtained New Horizons LORRI images to measure the cosmic optical background (COB) intensity integrated over 0.4 μm ≲ λ ≲ 0.9 μm. The survey comprises 16 high-Galactic-latitude fields selected to minimize scattered diffuse Galactic light (DGL) from the Milky Way, as well as scattered light from bright stars. This work supersedes an earlier analysis based on observations of one of the present fields. Isolating the COB contribution to the raw total sky levels measured in the fields requires subtracting the remaining scattered light from bright stars and galaxies, intensity from faint stars within the fields fainter than the photometric detection limit, and the DGL foreground. DGL is estimated from 350 μm and 550 μm intensities measured by the Planck High Frequency Instrument, using a new self-calibrated indicator based on the 16 fields augmented with eight additional DGL calibration fields obtained as part of the survey. The survey yields a highly significant detection (6.8σ) of the COB at 11.16 ± 1.65 (1.47 sys, 0.75 ran) nW m−2 sr−1 at the LORRI pivot wavelength of 0.608 μm. The estimated integrated intensity from background galaxies, 8.17 ± 1.18 nW m−2 sr−1, can account for the great majority of this signal. The rest of the COB signal, 2.99 ± 2.03 (1.75 sys, 1.03 ran) nW m−2 sr−1, is formally classified as anomalous intensity but is not significantly different from zero. The simplest interpretation is that the COB is completely due to galaxies.

Black hole pair revealed Binary supermassive black hole systems should be quite common, as the products of mergers between large galaxies, most of them with a black hole at their centre. In a trawl for novel quasars in the Sloan Digital Sky Survey, Todd Boroson and Tod Lauer have now uncovered one such object, J153636.22+044127.0. It shows two broad-line emission systems with different redshifts — 0.3727 and 0.3889 — equivalent to a velocity difference of 3,500 kilometres per second. They interpret the object as a binary system of two black holes, with masses of 10 7.3 and 10 8.9 solar masses separated by about 0.1 parsec and with an orbital period of about 100 years. The discovery of this object provides support for theories that predict the formation of binary black holes during galactic mega-mergers. The role of mergers in producing galaxies, together with the finding that most large galaxies harbour black holes in their nuclei, implies that binary supermassive black hole systems should be common. This study reports that the quasar SDSS J153636.22+044127.0 is a candidate binary, and shows two broad-line emission systems, separated in velocity by 3,500 km s −1 . The role of mergers in producing galaxies, together with the finding that most large galaxies harbour black holes in their nuclei 1 , implies that binary supermassive black hole systems should be common. Here we report that the quasar SDSS J153636.22+044127.0 is a plausible example of such a system. This quasar shows two broad-line emission systems, separated in velocity by 3,500 km s -1 . A third system of unresolved absorption lines has an intermediate velocity. These characteristics are unique among known quasars. We interpret this object as a binary system of two black holes, having masses of 10 7.3 and 10 8.9 solar masses separated by ∼0.1 parsec with an orbital period of ∼100 years.

Gravitationally magnified images of a faint galaxy from only 500 million years after the Big Bang suggest that galaxies of that age may be the dominant source of the radiation responsible for the re-ionization of the intergalactic medium. A young galaxy captured by a cosmic lens Young galaxies at a cosmic age of less than 500 million years remain largely unexplored because they are at or beyond the sensitivity limits of current large telescopes. This paper reports the use of strong gravitational lensing from a massive cluster of galaxies to observe a galaxy from the early Universe, at a redshift of z ≈ 9.6, equivalent to a cosmic age of approximately 490 million years. The authors suggest that because faint galaxies seem to be abundant at such a young cosmic age they are probably the dominant source for the early re-ionization of the intergalactic medium. Re-ionization of the intergalactic medium occurred in the early Universe at redshift z  ≈ 6–11, following the formation of the first generation of stars 1 . Those young galaxies (where the bulk of stars formed) at a cosmic age of less than about 500 million years ( z  ≲ 10) remain largely unexplored because they are at or beyond the sensitivity limits of existing large telescopes. Understanding the properties of these galaxies is critical to identifying the source of the radiation that re-ionized the intergalactic medium. Gravitational lensing by galaxy clusters allows the detection of high-redshift galaxies fainter than what otherwise could be found in the deepest images of the sky 2 . Here we report multiband observations of the cluster MACS J1149+2223 that have revealed (with high probability) a gravitationally magnified galaxy from the early Universe, at a redshift of z = 9.6 ± 0.2 (that is, a cosmic age of 490 ± 15 million years, or 3.6 per cent of the age of the Universe). We estimate that it formed less than 200 million years after the Big Bang (at the 95 per cent confidence level), implying a formation redshift of ≲14. Given the small sky area that our observations cover, faint galaxies seem to be abundant at such a young cosmic age, suggesting that they may be the dominant source for the early re-ionization of the intergalactic medium.

We present the final legacy version of stellar photometry for the Panchromatic Hubble Andromeda Treasury (PHAT) survey. We have reprocessed all of the Hubble Space Telescope Wide Field Camera 3 and Advanced Camera for Surveys near-ultraviolet (F275W, F336W), optical (F475W, F814W), and near-infrared (F110W, F160W) imaging from the PHAT survey using an improved method that optimized the survey depth and chip-gap coverage by including all overlapping exposures in all bands in the photometry. An additional improvement was gained through the use of charge transfer efficiency (CTE)–corrected input images, which provide more complete star finding as well as more reliable photometry for the NUV bands, which had no CTE correction in the previous version of the PHAT photometry. While this method requires significantly more computing resources and time than earlier versions where the photometry was performed on individual pointings, it results in smaller systematic instrumental completeness variations as demonstrated by cleaner maps in stellar density, and it results in optimal constraints on stellar fluxes in all bands from the survey data. Our resulting catalog has 138 million stars, 18% more than the previous catalog, with lower density regions gaining as much as 40% more stars. The new catalog produces nearly seamless population maps that show relatively well-mixed distributions for populations associated with ages older than 1–2 Gyr and highly structured distributions for the younger populations.

Wind-blown sand or ice dunes are known on Earth, Mars, Venus, Titan, and comet 67P/Churyumov-Gerasimenko. Telfer et al. used images taken by the New Horizons spacecraft to identify dunes in the Sputnik Planitia region on Pluto (see the Perspective by Hayes). Modeling shows that these dunes could be formed by sand-sized grains of solid methane ice transported in typical Pluto winds. The methane grains could have been lofted into the atmosphere by the melting of surrounding nitrogen ice or blown down from nearby mountains. Understanding how dunes form under Pluto conditions will help with interpreting similar features found elsewhere in the solar system. Science , this issue p. 992 ; see also p. 960 Images from New Horizons show dunes on Pluto, probably formed from sand-sized grains of solid methane. The surface of Pluto is more geologically diverse and dynamic than had been expected, but the role of its tenuous atmosphere in shaping the landscape remains unclear. We describe observations from the New Horizons spacecraft of regularly spaced, linear ridges whose morphology, distribution, and orientation are consistent with being transverse dunes. These are located close to mountainous regions and are orthogonal to nearby wind streaks. We demonstrate that the wavelength of the dunes (~0.4 to 1 kilometer) is best explained by the deposition of sand-sized (~200 to ~300 micrometer) particles of methane ice in moderate winds (<10 meters per second). The undisturbed morphology of the dunes, and relationships with the underlying convective glacial ice, imply that the dunes have formed in the very recent geological past.