Search NASA⌕ Search

SEARCH · Search NASA

Results for “Population III stars”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Distortions of the cosmic microwave background spectrum by dust

The effects of dust in the early universe on the spectrum of the cosmic microwave background are considered, taking into account the effects of a pregalactic generation of stars. It is shown that observed distortions of the background spectrum from that of a black body at 3 K could be due to emission by silicate dust grains at a metal abundance of 0.00001 by mass and with a substantial energy input, which represent the remnants of population III stars. Attempts to fit the microwave background spectrum to the model of Rees (1978) in which the entire cosmic background is accounted for by grain emission are shown to require an implausible value for the metal abundance at early epochs, and not to agree with the millimeter and submillimeter spectrum observed by Woody and Richards (1979).

Rowan-Robinson, M.↗
NASA NTRS2005

Cosmic Infrared Background and Early Galaxy Evolution

The cosmic infrared background (CIB) reflects the sum total of galactic luminosities integrated over the entire age of the universe. From its measurement the red-shifted starlight and dust-absorbed and re-radiated starlight of the CIB can be used to determine (or constrain) the rates of star formation and metal production as a function of time and deduce information about objects at epochs currently inaccessible to telescopic studies. This review discusses the state of current CIB measurements and the (mostly space-based) instruments with which these measurements have been made, the obstacles (the various foreground emissions) and the physics behind the CIB and its structure. Theoretical discussion of the CIB levels can now be normalized to the standard cosmological model narrowing down theoretical uncertainties. We review the information behind and theoretical modeling of both the mean (isotropic) levels of the CIB and their fluctuations. The CIB is divided into three broad bands: near-IR (NIR), mid-IR (MIR) and far-IR (FIR). For each of the bands we review the main contributors to the CIB flux and the epochs at which the bulk of the flux originates. We also discuss the data on the various quantities relevant for correct interpretation of the CIB levels: the star-formation history, the present-day luminosity function measurements, resolving the various galaxy contributors to the CIB, etc. The integrated light of all galaxies in the deepest NIR galaxy counts to date fails to match the observed mean level of the CIB, probably indicating a significant high-redshift contribution to the CIB. Additionally, Population III stars should have left a strong and measurable signature via their contribution to the CIB anisotropies for a wide range of their formation scenarios, and measuring the excess CIB anisotropies coming from high z would provide direct information on the epoch of the first stars.

Kashlinsky, Alexander↗
NASA NTRS1988

Needling the early universe

The possibility that the whole microwave background can be produced by a bright population of pregalactic stars at a redshift of a few hundred is explored. The radiation is thermalized by a combination of amorphous silicate, amorphous carbon, graphite, and needle-shaped conducting grains which give rise to the opacity needed at wavelengths greater than 3 cm. The occurrence of distortion in a primordial microwave background spectrum due to its interaction with Population III stars and dust is investigated. The possibility of producing deviations small enough to be consistent with the best available observations, but still detectable by COBE, is considered.

Hawkins, Isabel↗
NASA NTRS2021

RELICS-DP7: Spectroscopic Confirmation of a Dichromatic Primeval Galaxy atz∼7

We report the discovery of a spectroscopically confirmed strong Lyαemitter atz=7.0281±0.0003, observed as part of the Reionization Lensing Cluster Survey(RELICS). This galaxy, dubbed“Dichromatic Primeval Galaxy”atz∼7(DP7), shows two distinct components. While fairly unremarkable in terms of its ultraviolet(UV)luminosity(~L0.3UV*,whereLUV*is the characteristic luminosity), DP7 has one of the highest observed Lyαequivalent widths(EWs)amongLyαemitters atz>6(>200Åin the rest frame). The strong Lyαemission generally suggests a young metal-poor, low-dust galaxy; however, we find that the UV slopeβof the galaxy as a whole is redder than typical star-forming galaxies at these redshifts,−1.13±0.84, likely indicating, on average, a considerable amount of dust obscuration, or an older stellar population. When we measureβfor the two components separately, however, we find evidence of differing UVcolors, suggesting two separate stellar populations. Also, we find that Lyαis spatially extended and likely larger than the galaxy size, hinting to the possible existence of a Lyαhalo. Rejuvenation or merging events could explain these results.Either scenario requires an extreme stellar population, possibly including a component of Population III stars, or an obscured active galactic nucleus. DP7, with its low UV luminosity and high LyαEW, represents the typical galaxies that are thought to be the major contribution to the reionization of the universe, and for this reason DP7 is an excellent target for follow-up with the James Webb Space Telescope

Debora Pelliccia↗
NASA NTRS2007

GRBs: The Most Distant Signposts in our Universe

Gamma-Ray Bursts (GRBs) are the most powerful photon sources in the Universe, rivaled only by supernovae in the magnitude of their energy release. In 1997 GRB were found to originate in host galaxies at cosmological distances, revealing the total energy of their explosions to be an astounding approx.10(exp 52) - 10(exp 53)ergs. GRB durations span over five orders of magnitude, ranging from milliseconds to thousands of seconds. The underlying sources of the energy release remain, however, unknown. Leading candidates are mergers, either of two neutron stars or of a black hole and a neutron star, and core collapses of very massive stars, called "collapsars". To date the furthest GRB galaxy has been found at a cosmological redshift of 6.29, very close to the most distant quasar (at z=6.4). Since the Swift satellite continues to observe these phenomena at a rate of approx.120 per year, and with the upcoming launch of GLAST with two burst instruments on board, we will be able to use GRBs as beacons to probe very high redshifts. Thus bursts found at 6<z<20 can be efficient probes of the intergalactic medium, the first (population III) stars and the early stages of galaxy formation.

Kouveliotou, Chryssa↗
DOE OSTI2021

Missing in axion: Where are XENON1T’s big black holes?

We pioneer the black hole mass gap as a powerful new tool for constraining new particles. A new particle that couples to the Standard Model – such as an axion – acts as an additional source of loss in the cores of population-III stars, suppressing mass lost due to winds and quenching the pair-instability. This results in heavier astrophysical black holes. As an example, using stellar simulations we show that the solar axion explanation of the recent XENON1T excess implies astrophysical black holes of ~56M ⊙ , squarely within the black hole mass gap predicted by the Standard Model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Singularities in the gravitational capture of dark matter through long-range interactions

Here, we re-examine the gravitational capture of dark matter (DM) through long-range interactions. We demonstrate that neglecting the thermal motion of target particles, which is often a good approximation for short-range capture, results in parametrically inaccurate results for long-range capture. When the particle mediating the scattering process has a mass that is small in comparison to the momentum transfer in scattering events, correctly incorporating the thermal motion of target particles results in a quadratic, rather than logarithmic, sensitivity to the mediator mass, which substantially enhances the capture rate. We quantitatively assess the impact of this finite temperature effect on the captured DM population in the Sun as a function of mediator mass. We find that capture of DM through light dark photons, as in e.g. mirror DM, can be powerfully enhanced, with self-capture attaining a geometric limit over much of parameter space. For visibly-decaying dark photons, thermal corrections are not large in the Sun, but may be important in understanding long-range DM capture in more massive bodies such as Population III stars. We additionally provide the first calculation of the long-range DM self-evaporation rate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

The DECam MAGIC Survey: Spectroscopic Follow-up of the Most Metal-poor Stars in the Distant Milky Way Halo *

In this work, we present high-resolution spectroscopic observations for six metal-poor stars with [Fe/H] < –3 (including one with [Fe/H] < –4), selected using narrowband Ca ii HK photometry from the DECam MAGIC Survey. The spectroscopic data confirm the accuracy of the photometric metallicities and allow for the determination of chemical abundances for 16 elements, from carbon to barium. The program stars have chemical abundances consistent with the [Fe/H] < –3 range. A kinematic/dynamical analysis suggests that all program stars belong to the distant Milky Way halo population (heliocentric distances 35 < d helio /kpc ≲ 55), including three with high-energy orbits that might have been associated with the Magellanic system and one, J0026−5445, having parameters consistent with being a member of the Sagittarius stream. The remaining two stars show kinematics consistent with the Gaia-Sausage/Enceladus dwarf galaxy merger. J0433−5548, with [Fe/H] = –4.12, is a carbon-enhanced ultra metal-poor star, with [C/Fe] = +1.73. This star is believed to be a bona fide second-generation star, and its chemical abundance pattern was compared with yields from metal-free supernova models. Results suggest that J0433−5548 could have been formed from a gas cloud enriched by a single supernova explosion from an ∼11 M ⊙ star in the early Universe. The successful identification of such objects demonstrates the reliability of photometric metallicity estimates, which can be used for target selection and statistical studies of faint targets in the Milky Way and its satellite population. These discoveries illustrate the power of measuring chemical abundances of metal-poor Milky Way halo stars to learn more about early galaxy formation and evolution.

CEMP stars↗
DOE OSTI2023

A Stochastic Approach to Reconstruct Gamma-Ray-burst Light Curves

Gamma-ray bursts (GRBs), as they are observed at high redshift ( z = 9.4), are vital to cosmological studies and investigating Population III stars. To tackle these studies, we need correlations among relevant GRB variables with the requirement of small uncertainties on their variables. Thus, we must have good coverage of GRB light curves (LCs). However, gaps in the LC hinder the precise determination of GRB properties and are often unavoidable. Therefore, extensive categorization of GRB LCs remains a hurdle. We address LC gaps using a stochastic reconstruction, wherein we fit two preexisting models (the Willingale model; W07; and a broken power law; BPL) to the observed LC, then use the distribution of flux residuals from the original data to generate data to fill in the temporal gaps. We also demonstrate a model-independent LC reconstruction via Gaussian processes. At 10% noise, the uncertainty of the end time of the plateau, its correspondent flux, and the temporal decay index after the plateau decreases by 33.3%, 35.03%, and 43.32% on average for the W07, and by 33.3%, 30.78%, 43.9% for the BPL, respectively. The uncertainty of the slope of the plateau decreases by 14.76% in the BPL. After using the Gaussian process technique, we see similar trends of a decrease in uncertainty for all model parameters for both the W07 and BPL models. These improvements are essential for the application of GRBs as standard candles in cosmology, for the investigation of theoretical models, and for inferring the redshift of GRBs with future machine-learning analyses.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2012

Effect of Population III Multiplicity on Dark Star Formation

We numerically study the mutual interaction between dark matter (DM) and Population III (Pop III) stellar systems in order to explore the possibility of Pop III dark stars within this physical scenario. We perform a cosmological simulation, initialized at z approx. 100, which follows the evolution of gas and DM. We analyze the formation of the first mini halo at z approx. 20 and the subsequent collapse of the gas to densities of 10(exp 12)/cu cm. We then use this simulation to initialize a set of smaller-scale 'cut-out' simulations in which we further refine the DM to have spatial resolution similar to that of the gas. We test multiple DM density profiles, and we employ the sink particle method to represent the accreting star-forming region. We find that, for a range of DM configurations, the motion of the Pop III star-disk system serves to separate the positions of the protostars with respect to the DM density peak, such that there is insufficient DM to influence the formation and evolution of the protostars for more than approx. 5000 years. In addition, the star-disk system causes gravitational scattering of the central DM to lower densities, further decreasing the influence of DM over time. Any DM-powered phase of Pop III stars will thus be very short-lived for the typical multiple system, and DM will not serve to significantly prolong the life of Pop III stars.

Stacy, Athena↗
NASA NTRS2005

Tracing the First Stars with Fluctuations of the Cosmic Infrared Background

The deepest space- and ground-based observations find metal-enriched galaxies at cosmic times when the Universe was less than 1 Gyr old. These stellar populations had to be preceded by the metal-free first stars, known as 'population III'. Recent cosmic microwave background polarization measurements indicate that stars started forming early-when the Universe was 5200 Myr old. It is now thought that population III stars were significantly more massive than the present metal-rich stellar populations. Although such sources will not be individually detectable by existing or planned telescopes, they would have produced significant cosmic infrared background radiation in the near-infrared, whose fluctuations reflect the conditions in the primordial density field. Here we report a measurement of diffuse flux fluctuations after removing foreground stars and galaxies. The anisotropies exceed the instrument noise and the more local foregrounds; they can be attributed to emission from population III stars, at an era dominated by these objects.

Kashlinsky, A.↗
DOE OSTI2021

First Star Formation in the Presence of Primordial Magnetic Fields

It has been recently claimed that primordial magnetic fields could relieve the cosmological Hubble tension. Fields of sufficient strength to relieve this tension would result in a magnetic field whose Alfvén velocity, va, is comparable to the speed of sound, cs, at the start of structure formation. We consider the impact of such fields on the formation of the first cosmological objects, minihalos (<10 6 M ⊙ ), forming stars with zoom-in cosmological simulations tracking a single such minihalo. We seed each simulation with present-day field strengths of 2 × 10 –12 –2 × 10 –10 G corresponding to initial ratios of Alfvén velocity to the speed of sound of va/cs ≈ 0.03–3. We find that when va/cs=1, the effects are modest. However, when va ~ cs, the starting time of the gravitational collapse is delayed and the duration extended as much as by Δz = 2.5 in redshift. When va > cs, the collapse is completely suppressed and the minihalos continue to grow and are unlikely to collapse until reaching the atomic cooling limit. Employing current observational limits on primordial magnetic fields we conclude that inflationaryproduced primordial magnetic fields could have a significant impact on first star formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Induced Metal-free Star Formation around a Massive Black Hole Seed

The direct formation of a massive black hole is a potential seeding mechanism of the earliest observed supermassive black holes. We investigate how the existence of a massive black hole seed impacts the ionization and thermal state of its pre-galactic host halo and subsequent star formation. We show that its X-ray radiation ionizes and heats the medium, enhancing H 2 formation in shielded regions, within the nuclear region in the span of a million years. The enhanced molecular cooling triggers the formation of a ~10 4 M⊙ metal-free stellar cluster at a star formation efficiency of ~0.1% in a single event. Star formation occurs near the edges of the H ii region that is partially ionized by X-rays; thus, the initial size depends on the black hole properties and surrounding environment. Furthermore, the simulated metal-free galaxy has an initial half-light radius of ~10 pc but expands to ~50 pc after 10 million years because of the outward velocities of their birth clouds. Supernova feedback then quenches any further star formation for tens of millions of years, allowing the massive black hole to dominate the spectrum once the massive metal-free stars die.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2014

The First Stars: A Low-Mass Formation Mode

We perform numerical simulations of the growth of a Population III stellar system under photodissociating feedback. We start from cosmological initial conditions at z = 100, self-consistently following the formation of a minihalo at z = 15 and the subsequent collapse of its central gas to high densities. The simulations resolve scales as small as approx. 1 AU, corresponding to gas densities of 10(exp 16)/cu cm. Using sink particles to represent the growing protostars, we evolve the stellar system for the next 5000 yr. We find that this emerging stellar group accretes at an unusually low rate compared with minihalos which form at earlier times (z = 20-30), or with lower baryonic angular momentum. The stars in this unusual system will likely reach masses ranging from <1Stellar Mass to approx. 5 Stellar Mass by the end of their main-sequence lifetimes, placing them in the mass range for which stars will undergo an asymptotic giant branch (AGB) phase. Based upon the simulation, we predict the rare existence of Population III stars that have survived to the present day and have been enriched by mass overflow from a previous AGB companion.

Low-Mass↗
NASA NTRS1980

Velocity dispersion of M87 using a population model

The velocity dispersion of M 87 (NGC 4486) is determined using (1) a single star of class K0 III and (2) two different population models to represent the spectral region of the G-band. Although the models fit the overall spectrum better than the single-star, there is only a small difference in the derived velocity dispersion. This work revises the earlier velocity dispersion result of Brandt and Roosen (1969) down to 350 km/sec, in agreement with Faber and Jackson (1976) and Sargent et al. (1978).

Angione, R. J.↗
DOE OSTI2021

The COMBS Survey – III. The chemodynamical origins of metal-poor bulge stars

The characteristics of the stellar populations in the Galactic bulge inform and constrain the Milky Way’s formation and evolution. The metal-poor population is particularly important in light of cosmological simulations, which predict that some of the oldest stars in the Galaxy now reside in its centre. The metal-poor bulge appears to consist of multiple stellar populations that require dynamical analyses to disentangle. In this work, we undertake a detailed chemodynamical study of the metal-poor stars in the inner Galaxy. Using R ~ 20000 VLT/GIRAFFE spectra of 319 metal-poor (-2.55 dex ≤ [Fe/H] ≤ 0.83 dex, with $\overline{[Fe/H]}$ = -0.84 dex) stars, we perform stellar parameter analysis and report 12 elemental abundances (C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Zn, Ba, and Ce) with precisions of ≈0.10 dex. Based on kinematic and spatial properties, we categorize the stars into four groups, associated with the following Galactic structures: the inner bulge, the outer bulge, the halo, and the disc. We find evidence that the inner and outer bulge population is more chemically complex (i.e. higher chemical dimensionality and less correlated abundances) than the halo population. This result suggests that the older bulge population was enriched by a larger diversity of nucleosynthetic events. We also find one inner bulge star with a [Ca/Mg] ratio consistent with theoretical pair-instability supernova yields and two stars that have chemistry consistent with globular cluster stars.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2019

Near-infrared Spectroscopy of Galaxies During Reionization: Measuring C III] in a Galaxy at z = 7.5

We present Keck/MOSFIRE H-band spectroscopy targeting C III] λ1907, 1909 in a z = 7.5056 galaxy previously identified via Lyα emission. We detect strong line emission at 1.621 ± 0.002 mm with a line flux of (2.63 ± 0.52) × 10−18 erg s−1cm−2. We tentatively identify this line as [C III] λ1907, but we are unable to detect C III] λ1909 owing to sky emission at the expected location. This gives a galaxy systemic redshift, zsys = 7.5032 ± 0.0003, with a velocity offset to Lyα of DvLya = 88 ± 27 km s−1. The ratio of combined C III]/Lyα is 0.30–0.45, one of the highest values measured for any z > 2 galaxy. We do not detect Si III] λλ1883, 1892, and place an upper limit on Si III]/C III] < 0.35 (2σ). Comparing our results to photoionization models, the C III] equivalent width (WC III] = 16.23 ± 2.32 Å), low Si III]/C III] ratio, and high implied [O III] equivalent width (from the Spitzer/IRAC [3.6]–[4.5] ~- 0.8 mag color) require subsolar metallicities (Z ~- 0.1–0.2 Zsun) and a high ionization parameter, log U >~ 1.5. These results favor models that produce higher ionization, such as the BPASS models for the photospheres of high-mass stars, and that include both binary stellar populations and/or an IMF that extends to 300 Me. The combined C III] equivalent width and [3.6]–[4.5] color are more consistent with ionization from young stars than active galactic nuclei (AGNs); however, we cannot rule out ionization from a combination of an AGN and young stars. We make predictions for James Webb Space Telescope spectroscopy using these different models, which will ultimately test the nature of the ionizing radiation in this source.

reionization↗
NASA NTRS1979

The evolution of rotating stars. III - Predicted surface rotation velocities for stars which conserve total angular momentum

Predicted surface rotation velocities for Population I stars at 10, 7, 5, 3, and 1.5 solar masses are presented. The surface velocities were computed for angular momentum with no radial redistribution, complete redistribution, and partial redistribution as predicted by consideration of circulation currents in rotating stars. Near the main sequence, rotational effects can reduce the moment of inertia of a star, so nonrotating models underestimate the expected velocities for evolving stars. On the red giant branch, angular momentum redistribution reduces the surface velocity by a factor of 2 or more, relative to the velocity expected for no radial redistribution. This removes the discrepancy between predicted and observed rotation rates for the K giants and makes it unlikely that these stars lose significant amounts of angular momentum by stellar winds. Calculations indicate that improved observations of the red giants in the Hyades cluster can be used to determine how angular momentum is redistributed by convection

Endal, A. S.↗