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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

The Lyman continuum escape fraction of the cosmic horseshoe: a test of indirect estimates

High-redshift star-forming galaxies are likely responsible for the reionization of the universe, yet direct detection of their escaping ionizing (Lyman continuum [LyC]) photons has proven to be extremely challenging. In this study, we search for escaping LyC of the Cosmic Horseshoe, a gravitationally lensed, star-forming galaxy at z = 2.38 with a large magnification of ∼24. Transmission at wavelengths of low-ionization interstellar absorption lines in the rest-frame ultraviolet suggests a patchy, partially transparent interstellar medium. This makes it an ideal candidate for direct detection of the LyC. We obtained a 10-orbit Hubble near-UV image using the Wide Field Camera 3 (WFC3)/UVIS F275W filter that probes wavelengths just below the Lyman limit at the redshift of the Horseshoe in an attempt to detect escaping LyC radiation. After fully accounting for the uncertainties in the opacity of the intergalactic medium (IGM) and accounting for the charge transfer inefficiency in the WFC3 CCDs, we find a 3σ upper limit for the relative escape fraction of f{sub esc,rel}<0.08. This value is a factor of five lower than the value (0.4) predicted by the 40% transmission in the low-ion absorption lines. Though possible, it is unlikely that the nondetection is due to a high-opacity line of sight through the IGM (<20% chance). We discuss several possible causes for the discrepancy between the escape fraction and the covering fraction and consider the implications for future attempts at both direct LyC detection and indirect estimates of the escape fraction.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Evolution of Dust-obscured Star Formation and Gas to z = 2.2 from HiZELS

We investigate the far-infrared (far-IR) properties of galaxies selected via deep, narrow-band imaging of the Hα emission line in four redshift slices from z=0.40--2.23 over ∼1 deg{sup 2} as part of the High-redshift Emission Line Survey (HiZELS). We use a stacking approach in the Herschel PACS/SPIRE far-IR bands, along with 850 μm imaging from SCUBA-2 and Very Large Array 1.4 GHz imaging, to study the evolution of the dust properties of Hα-emitters selected above an evolving characteristic luminosity threshold, 0.2L{sub Hα}{sup ⋆}(z). We investigate the relationship between the dust temperatures, T {sub dust}, and the far-infrared luminosities, L {sub IR}, of our stacked samples, finding that our Hα-selection identifies cold, low-L {sub IR} galaxies (T{sub dust}∼14 K; log[L{sub IR}/L{sub ⊙}]∼9.9) at z = 0.40, and more luminous, warmer systems (T{sub dust}∼34 K; log[L{sub IR}/L{sub ⊙}]∼11.5) at z = 2.23. Using a modified graybody model, we estimate “characteristic sizes” for the dust-emitting regions of Hα-selected galaxies of ∼0.5 kpc, nearly an order of magnitude smaller than their stellar continuum sizes, which may provide indirect evidence of clumpy interstellar medium structure. Lastly, we use measurements of the dust masses from our far-IR stacking along with metallicity-dependent gas-to-dust ratios (δ{sub GDR}) to measure typical molecular gas masses of ∼1×10{sup 10} M{sub ⊙} for these bright Hα-emitters. The gas depletion timescales are shorter than the Hubble time at each redshift, suggesting probable replenishment of their gas reservoirs from the intergalactic medium. Based on the number density of Hα-selected galaxies, we find that typical star-forming galaxies brighter than 0.2L{sub Hα}{sup ⋆}(z) comprise a significant fraction (35 ± 10%) of the total gas content of the universe, consistent with the predictions of the latest state-of-the-art cosmological simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

The ring around SN1987A

Stars in the 9-40 solar mass range play a prominent role in the hydrodynamical and chemical evolution of galaxies. Their stellar winds and supernova explosions are believed to create the hot component of the interstellar medium (ISM). In some galactic disks, the kiloparsec sized super bubbles formed around clusters of massive stars may blow out of the disk plane and release hot, metal enriched gas into the galaxy's halo. Additionally, the expanding shock front of a super bubble in the disk may trigger additional star formation. Furthermore, similar processes probably drive the galactic winds associated with star burst nuclei that enrich the intracluster and intergalactic mediums. Nonetheless, the explosion of a blue super giant in the Large Magellanic Cloud (LMC), SN1987A, illuminated the incompleteness of our understanding of massive stars. Evolutionary models of massive stars do not synthesize the observed super giant populations in either the Milky Way or LMC. Our modeling of the formation of SN1987A's ring will improve our knowledge of both the post-main-sequence evolution of massive stars and their coupling to the ISM in galaxies.

Martin, Crystal L.↗
DOE OSTI2016

University of Arizona High Energy Physics Program at the Cosmic Frontier 2014-2016

This is the final technical report from the University of Arizona High Energy Physics program at the Cosmic Frontier covering the period 2014-2016. The work aims to advance the understanding of dark energy using the Large Synoptic Survey Telescope (LSST). Progress on the engineering design of the power supplies for the LSST camera is discussed. A variety of contributions to photometric redshift measurement uncertainties were studied. The effect of the intergalactic medium on the photometric redshift of very distant galaxies was evaluated. Computer code was developed realizing the full chain of calculations needed to accurately and efficiently run large-scale simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

PROBING THE OUTSKIRTS OF THE EARLY-STAGE GALAXY CLUSTER MERGER A1750

We present results from recent Suzaku and Chandra X-ray and Multiple Mirrior Telescope optical observations of the strongly merging “double cluster” A1750 out to its virial radius, both along and perpendicular to a putative large-scale structure filament. Some previous studies of individual clusters have found evidence for ICM entropy profiles that flatten at large cluster radii, as compared with the self-similar prediction based on purely gravitational models of hierarchical cluster formation, and gas fractions that rise above the mean cosmic value. Weakening accretion shocks and the presence of unresolved cool gas clumps, both of which are expected to correlate with large-scale structure filaments, have been invoked to explain these results. In the outskirts of A1750, we find entropy profiles that are consistent with self-similar expectations, and gas fractions that are consistent with the mean cosmic value, both along and perpendicular to the putative large-scale filament. Thus, we find no evidence for gas clumping in the outskirts of A1750, in either direction. This may indicate that gas clumping is less common in lower temperature (kT ≈ 4 keV), less massive systems, consistent with some (but not all) previous studies of low-mass clusters and groups. Cluster mass may, therefore, play a more important role in gas clumping than dynamical state. Finally, we find evidence for diffuse, cool (<1 keV) gas at large cluster radii (R{sub 200}) along the filament, which is consistent with the expected properties of the denser, hotter phase of the warm–hot intergalactic medium.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2008

Xenia: A Probe of Cosmic Chemical Evolution

Xenia is a concept study for a medium-size astrophysical cosmology mission addressing the Cosmic Origins key objective of NASA's Science Plan. The fundamental goal of this objective is to understand the formation and evolution of structures on various scales from the early Universe to the present time (stars, galaxies and the cosmic web). Xenia will use X-and y-ray monitoring and wide field X-ray imaging and high-resolution spectroscopy to collect essential information from three major tracers of these cosmic structures: the Warm Hot Intergalactic Medium (WHIM), Galaxy Clusters and Gamma Ray Bursts (GRBs). Our goal is to trace the chemo-dynamical history of the ubiquitous warm hot diffuse baryon component in the Universe residing in cosmic filaments and clusters of galaxies up to its formation epoch (at z =0-2) and to map star formation and galaxy metal enrichment into the re-ionization era beyond z ~ 6. The concept of Xenia (Greek for "hospitality") evolved in parallel with the Explorer of Diffuse Emission and GRB Explosions (EDGE), a mission proposed by a multinational collaboration to the ESA Cosmic Vision 2015. Xenia incorporates the European and Japanese collaborators into a U.S. led mission that builds on the scientific objectives and technological readiness of EDGE.

Kouveliotou, Chryssa↗
DOE OSTI2016

PREDOMINANTLY LOW METALLICITIES MEASURED IN A STRATIFIED SAMPLE OF LYMAN LIMIT SYSTEMS AT Z = 3.7

We measured metallicities for 33 z = 3.4–4.2 absorption line systems drawn from a sample of H i-selected-Lyman limit systems (LLSs) identified in Sloan Digital Sky Survey (SDSS) quasar spectra and stratified based on metal line features. We obtained higher-resolution spectra with the Keck Echellette Spectrograph and Imager, selecting targets according to our stratification scheme in an effort to fully sample the LLS population metallicity distribution. We established a plausible range of H i column densities and measured column densities (or limits) for ions of carbon, silicon, and aluminum, finding ionization-corrected metallicities or upper limits. Interestingly, our ionization models were better constrained with enhanced α -to-aluminum abundances, with a median abundance ratio of [ α /Al] = 0.3. Measured metallicities were generally low, ranging from [M/H] = −3 to −1.68, with even lower metallicities likely for some systems with upper limits. Using survival statistics to incorporate limits, we constructed the cumulative distribution function (CDF) for LLS metallicities. Recent models of galaxy evolution propose that galaxies replenish their gas from the low-metallicity intergalactic medium (IGM) via high-density H i “flows” and eject enriched interstellar gas via outflows. Thus, there has been some expectation that LLSs at the peak of cosmic star formation ( z ≈ 3) might have a bimodal metallicity distribution. We modeled our CDF as a mix of two Gaussian distributions, one reflecting the metallicity of the IGM and the other representative of the interstellar medium of star-forming galaxies. This bimodal distribution yielded a poor fit. A single Gaussian distribution better represented the sample with a low mean metallicity of [M/H] ≈ −2.5.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2005

Weighing the Low-Redshift Lyman-alpha Forest

In 2003-2004, our FUSE research group prepared several major surveys of the amount of baryonic matter in the intergalactic medium (IGM), using the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. These surveys include measurements of the Lyman-alpha absorption line of neutral hydrogen (H I), the far-ultraviolet (1032,1038 Angstrom) doublet of highly ionized oxygen ( O VI), the higher Lyman-series lines (Ly-beta, Ly-gamma, etc) of H I, and the 977 Angstrom line of c III. As an overview, our FUSE spectroscopic studies, taken together with data from the Hubble Space Telescope, show that approximately 30% of the normal matter is contained in intergalactic hydrogen gas clouds (the Lyman-alpha forest). Another 5-10% resides in hotter gas at temperatures of 10(exp 5) to 10(exp 6) K, visible in 0 VI and C III absorption. Along with the matter attributed to galaxies, we have now accounted for approximately HALF of all the baryonic matter in the universe. Where is the other half? That matter my exist in even hotter gas, invisible through the ultraviolet absorption lines, but perhaps detectable through X-ray absorption lines of more highly ionized oxygen and neon.

Shull, Mike↗
DOE OSTI2016

Inferences from the distributions of fast radio burst pulse widths, dispersion measures, and fluences

The widths, dispersion measures (DMs), dispersion indices, and fluences of Fast Radio Bursts (FRBs) impose coupled constraints that all models must satisfy. The non-monotonic dependence of burst widths (after deconvolution of instrumental effects) on DMs excludes the intergalactic medium as the location of scattering that broadens the FRBs in time. Temporal broadening far greater than that of pulsars at similar high Galactic latitudes implies that scattering occurs close to the sources where high densities and strong turbulence or heterogeneity are plausible. FRB energetics are consistent with supergiant pulses from young, fast, high-field pulsars at cosmological distances. The distribution of FRB DMs is: (1) inconsistent with that of expanding clouds (such as SNRs); (2) inconsistent with space-limited source populations (such as the local Supercluster); and (3) consistent with intergalactic dispersion of a homogeneous source population at cosmological distances. Finally, the FRB log N–log S relation also indicates a cosmological distribution aside from the anomalously bright Lorimer burst.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

THE STRUCTURE OF THE CIRCUMGALACTIC MEDIUM OF GALAXIES: COOL ACCRETION INFLOW AROUND NGC 1097

We present Hubble Space Telescope far-UV spectra of four QSOs whose sightlines pass through the halo of NGC 1097 at impact parameters of ρ = 48–165 kpc. NGC 1097 is a nearby spiral galaxy that has undergone at least two minor merger events, but no apparent major mergers, and is relatively isolated with respect to other nearby bright galaxies. This makes NGC 1097 a good case study for exploring baryons in a paradigmatic bright-galaxy halo. Ly α absorption is detected along all sightlines and Si iii λ 1206 is found along the three sightlines with the smallest ρ ; metal lines of C ii, Si ii, and Si iv are only found with certainty toward the innermost sightline. The kinematics of the absorption lines are best replicated by a model with a disk-like distribution of gas approximately planar to the observed 21 cm H i disk, which is rotating more slowly than the inner disk, and into which gas is infalling from the intergalactic medium. Some part of the absorption toward the innermost sightline may arise either from a small-scale outflow or from tidal debris associated with the minor merger that gives rise to the well known “dog-leg” stellar stream that projects from NGC 1097. When compared to other studies, NGC 1097 appears to be a “typical” absorber, although the large dispersion in absorption line column density and equivalent width in a single halo goes perhaps some way toward explaining the wide range of these values seen in higher- z studies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

PLASMA EFFECTS ON EXTRAGALACTIC ULTRAHIGH-ENERGY COSMIC-RAY HADRON BEAMS IN COSMIC VOIDS. II. KINETIC INSTABILITY OF PARALLEL ELECTROSTATIC WAVES

The linear instability of an ultrarelativistic hadron beam in the unmagnetized intergalactic medium (IGM) is investigated with respect to the excitation of parallel electrostatic and electromagnetic fluctuations. This analysis is important for the propagation of extragalactic ultrarelativistic cosmic rays from their distant sources to Earth. As opposed to the previous paper, we calculate the minimum instability growth time for Lorentz-distributed cosmic rays which traverse the hot IGM. The growth times are orders of magnitude higher than the cosmic-ray propagation time in the IGM. Since the backreaction of the generated plasma fluctuations (plateauing) lasts longer than the propagation time, the cosmic-ray hadron beam can propagate to the Earth without losing a significant amount of energy to electrostatic turbulence.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Constraining the CMB optical depth through the dispersion measure of cosmological radio transients

The dispersion measure of extragalactic radio transients can be used to measure the column density of free electrons in the intergalactic medium. The same electrons also scatter the Cosmic Microwave Background (CMB) photons, affecting precision measurements of cosmological parameters. We explore the connection between the dispersion measure of radio transients existing during the Epoch of Reionization (EoR) and the total optical depth for the CMB showing that the existence of such transients would provide a new sensitive probe of the CMB optical depth. As an example, we consider the population of FRBs. Assuming they exist during the EoR, we show that: (i) such sources can probe the reionization history by measuring the optical depth to sub-percent accuracy, and (ii) they can be detected with high significance by an instrument such as the Square Kilometer Array.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Probing WHIM around galaxy clusters with fast radio bursts and the Sunyaev–Zel’dovich effect

We propose a new method to probe the warm hot intergalactic medium (WHIM) beyond the virial radius (R{sub 200}) of a cluster of galaxies, where X-ray observations are not easily achievable. In this method, we use dispersion measures (DMs) of fast radio bursts (FRBs) that appear behind the cluster and the Sunyaev–Zel’dovich (SZ) effect toward the cluster. The DMs reflect the density of the intracluster medium including the WHIM. If we observe a sufficient number of FRBs in the direction of the cluster, we can derive the density profile from the DMs. Similarly, we can derive the pressure profile from the SZ effect. By combining the density and the pressure profiles, the temperature profile can be obtained. Based on mock observations of nearby clusters, we find that the density of the WHIM will be determined even at >2 R{sub 200} from the cluster center when FRB observations with the Square Kilometre Array become available. The temperature can be derived out to r∼1.5 R{sub 200}, and the radius is limited by the current sensitivity of SZ observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

COS-burst: Observations of the Impact of Starburst-driven Winds on the Properties of the Circum-galactic Medium

We report on observations made with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope ( HST ) using background quasi-stellar objects to probe the circum-galactic medium (CGM) around 17 low-redshift galaxies that are undergoing or have recently undergone a strong starburst (the COS-Burst program). The sightlines extend out to roughly the virial radius of the galaxy halo. We construct control samples of normal star-forming low-redshift galaxies from the COS/ HST archive that match the starbursts in terms of galaxy stellar mass and impact parameter. We find clear evidence that the CGM around the starbursts differs systematically compared to the control galaxies. The Ly α , Si iii, C iv, and possibly O vi absorption lines are stronger as a function of impact parameter, and the ratios of the equivalent widths of C iv/Ly α and Si iii/Ly α are both higher than in normal star-forming galaxies. We also find that the widths and the velocity offsets (relative to v {sub sys}) of the Ly α absorption lines are significantly larger in the CGM of the starbursts, implying velocities of the absorbing material that are roughly twice the halo virial velocity. We show that these properties can be understood as a consequence of the interaction between a starburst-driven wind and the preexisting CGM. These results underscore the importance of winds driven from intensely star-forming galaxies in helping drive the evolution of galaxies and the intergalactic medium. They also offer a new probe of the properties of starburst-driven winds and of the CGM itself.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

A NEWLY FORMING COLD FLOW PROTOGALACTIC DISK, A SIGNATURE OF COLD ACCRETION FROM THE COSMIC WEB

How galaxies form from, and are fueled by, gas from the intergalactic medium (IGM) remains one of the major unsolved problems in galaxy formation. While the classical Cold Dark Matter paradigm posits galaxies forming from cooling virialized gas, recent theory and numerical simulations have highlighted the importance of cold accretion flows—relatively cool ( T ∼ few × 104 K) unshocked gas streaming along filaments into dark matter halos, including hot, massive, high-redshift halos. These flows are thought to deposit gas and angular momentum into the circumgalactic medium resulting in disk- or ring-like structures, eventually coalescing into galaxies forming at filamentary intersections. We earlier reported a bright, Ly α emitting filament near the QSO HS1549+19 at redshift z = 2.843 discovered with the Palomar Cosmic Web Imager. We now report that the bright part of this filament is an enormous ( R > 100 kpc) rotating structure of hydrogen gas with a disk-like velocity profile consistent with a 4 × 10{sup 12} M {sub ⊙} halo. The orbital time of the outer part of the what we term a “protodisk” is comparable to the virialization time and the age of the universe at this redshift. We propose that this protodisk can only have recently formed from cold gas flowing directly from the cosmic web.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

ON THE ORIGIN OF THE SCATTER BROADENING OF FAST RADIO BURST PULSES AND ASTROPHYSICAL IMPLICATIONS

Fast radio bursts (FRBs) have been identified as extragalactic sources that can probe turbulence in the intergalactic medium (IGM) and their host galaxies. To account for the observed millisecond pulses caused by scatter broadening, we examine a variety of possible electron density fluctuation models in both the IGM and the host galaxy medium. We find that a short-wave-dominated power-law spectrum of density, which may arise in highly supersonic turbulence with pronounced local dense structures of shock-compressed gas in the host interstellar medium (ISM), can produce the required density enhancements at sufficiently small scales to interpret the scattering timescale of FRBs. This implies that an FRB residing in a galaxy with efficient star formation in action tends to have a broadened pulse. The scaling of the scattering time with the dispersion measure (DM) in the host galaxy varies in different turbulence and scattering regimes. The host galaxy can be the major origin of scatter broadening, but contributes to a small fraction of the total DM. We also find that the sheet-like structure of the density in the host ISM associated with folded magnetic fields in a viscosity-dominated regime of magnetohydrodynamic (MHD) turbulence cannot give rise to strong scattering. Furthermore, valuable insights into the IGM turbulence concerning the detailed spatial structure of density and magnetic field can be gained from the observed scattering timescale of FRBs. Our results favor the suppression of micro-plasma instabilities and the validity of the collisional-MHD description of turbulence properties in the collisionless IGM.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Joint Bayesian Estimation of Quasar Continua and the Lyα Forest Flux Probability Distribution Function

We present a new Bayesian algorithm making use of Markov Chain Monte Carlo sampling that allows us to simultaneously estimate the unknown continuum level of each quasar in an ensemble of high-resolution spectra, as well as their common probability distribution function (PDF) for the transmitted Lyα forest flux. This fully automated PDF regulated continuum fitting method models the unknown quasar continuum with a linear principal component analysis (PCA) basis, with the PCA coefficients treated as nuisance parameters. The method allows one to estimate parameters governing the thermal state of the intergalactic medium (IGM), such as the slope of the temperature–density relation γ−1, while marginalizing out continuum uncertainties in a fully Bayesian way. Using realistic mock quasar spectra created from a simplified semi-numerical model of the IGM, we show that this method recovers the underlying quasar continua to a precision of ≃7% and ≃10% at z = 3 and z = 5, respectively. Given the number of principal component spectra, this is comparable to the underlying accuracy of the PCA model itself. Most importantly, we show that we can achieve a nearly unbiased estimate of the slope γ−1 of the IGM temperature–density relation with a precision of ±8.6% at z = 3 and ±6.1% at z = 5, for an ensemble of ten mock high-resolution quasar spectra. Applying this method to real quasar spectra and comparing to a more realistic IGM model from hydrodynamical simulations would enable precise measurements of the thermal and cosmological parameters governing the IGM, albeit with somewhat larger uncertainties, given the increased flexibility of the model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The eROSITA Final Equatorial-Depth Survey (eFEDS)

The eROSITA Final Equatorial Depth Survey (eFEDS), completed in survey mode during the calibration and performance verification phase of the eROSITA instrument on Spectrum Roentgen Gamma, delivers data at and beyond the final depth of the 4-yr eROSITA all-sky survey (eRASS:8), f 0.5–2 keV = 1.1 × 10 –14 erg s –1 cm –2 , over 140 deg 2 . It provides the first view of normal galaxy X-ray emission from X-ray binaries (XRBs) and the hot interstellar medium at the full depth of eRASS:8. We used the Heraklion Extragalactic Catalogue (HECATE) of galaxies to correlate with eFEDS X-ray sources and identify X-ray detected normal galaxies. This flux-limited X-ray survey is relatively free from selection effects and enables the study of integrated normal galaxy X-ray emission and its relation to galaxy parameters such as the stellar mass, star formation rate (SFR), and metallicity. We cross-correlated 32 646 eFEDS X-ray sources to 1181 HECATE normal galaxies and obtained 94 matches. We classified galaxies as star-forming, early-type, composite, and active galactic nuclei (AGN) using Sloan Digital Sky Survey (SDSS) and Six-degree Field (6dF) optical spectroscopy. The eFEDS field harbours 37 normal galaxies: 36 late-type (star-forming) galaxies and one early-type galaxy. There are 1.9 times as many normal galaxies as predicted by scaling relations via simulations, with an overabundance of late-type galaxies and a dearth of early-type galaxies. When compared with empirical relations, eFEDS dwarf galaxies with a high specific SFR have elevated L X /SFR at a fixed specific SFR and metallicity, indicating an increase in XRB emission due to low metallicity. We expect that eRASS:8 will detect 12 500 normal galaxies, the majority of which will be star-forming, with the caveat that there are unclassified sources in eFEDS and galaxy catalogue incompleteness issues that could increase the actual number of detected galaxies over these current estimates. eFEDS observations detected a rare population of galaxies – the metal-poor dwarf starbursts – that do not follow known scaling relations. eRASS is expected to discover significant numbers of these high-redshift analogues, which are important for studying the heating of the intergalactic medium at high redshift. Further investigation of the hot gas emission from normal galaxies and stochastic effects in the dwarf galaxy population are required to constrain their X-ray output.

79 ASTRONOMY AND ASTROPHYSICS↗