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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 343 records · Page 19
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DOE OSTI2020

Green Bank and Effelsberg Radio Telescope Searches for Axion Dark Matter Conversion in Neutron Star Magnetospheres

Axion dark matter (DM) may convert to radio-frequency electromagnetic radiation in the strong magnetic fields around neutron stars. The radio signature of such a process would be an ultranarrow spectral peak at a frequency determined by the mass of the axion particle. In this work, we analyze data we collected from the Robert C. Byrd Green Bank Telescope in the L band and the Effelsberg 100-m Telescope in the $\textit{L}$ band and $\textit{S}$ band from a number of sources expected to produce bright signals of axion-photon conversion, including the Galactic center of the Milky Way and the nearby isolated neutron stars RX J0720.4-3125 and RX J0806.4-4123. We find no evidence for axion DM and are able to set constraints on the existence of axion DM in the highly motivated mass range between ~ 5 and 11 μ eV with the strongest constraints to date on axions in the ~10–11 μ eV range.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Search for the chiral magnetic effect with isobar collisions at $\sqrt{s_{NN}}$ = 200 GeV by the STAR Collaboration at the BNL Relativistic Heavy Ion Collider

The chiral magnetic effect (CME) is predicted to occur as a consequence of a local violation of P and CP symmetries of the strong interaction amidst a strong electro-magnetic field generated in relativistic heavy-ion collisions. Experimental manifestation of the CME involves a separation of positively and negatively charged hadrons along the direction of the magnetic field. Previous measurements of the CME-sensitive charge-separation observables remain inconclusive because of large background contributions. In order to better control the influence of signal and backgrounds, the STAR Collaboration performed a blind analysis of a large data sample of approximately 3.8 billion isobar collisions of $^{96}_{44}$Ru + $^{96}_{44}$Ru and $^{96}_{40}$Zr + $^{96}_{40}$Zr at $\sqrt{s_{NN}}$ = 200 GeV. Prior to the blind analysis, the CME signatures are predefined as a significant excess of the CME-sensitive observables in Ru + Ru collisions over those in Zr + Zr collisions, owing to a larger magnetic field in the former. Here, a precision down to 0.4% is achieved, as anticipated, in the relative magnitudes of the pertinent observables between the two isobar systems. Observed differences in the multiplicity and flow harmonics at the matching centrality indicate that the magnitude of the CME background is different between the two species. No CME signature that satisfies the predefined criteria has been observed in isobar collisions in this blind analysis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Neutron stars as photon double-lenses: Constraining resonant conversion into ALPs

Axion-photon conversion is a prime mechanism to detect axion-like particles that share a coupling to the photon. We point out that in the vicinity of neutron stars with strong magnetic fields, magnetars, the effective photon mass receives comparable but opposite contributions from free electrons and the radiation field. This leads to an energy-dependent resonance condition for conversion that can be met for arbitrary light axions and leveraged when using systems with detected radio component. Using the magnetar SGR J1745-2900 as an exemplary source, we demonstrate that sensitivity to |g aγ | ~ 10 -12 GeV -1 or better can be gained for m a ≲ 10 -6 eV, with the potential to improve current constraints on the axion-photon coupling by more than one order of magnitude over a broad mass range. With growing insights into the physical conditions of magnetospheres of magnetars, the method hosts the potential to become a serious competitor to future experiments such as ALPS-II and IAXO in the search for axion-like particles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

The Simons Observatory: science goals and forecasts for the enhanced Large Aperture Telescope

We describe updated scientific goals for the wide-field, millimeter-wave survey that will be produced by the Simons Observatory (SO). Significant upgrades to the 6-meter SO Large Aperture Telescope (LAT) are expected to be complete by 2028, and will include a doubled mapping speed with 30,000 new detectors and an automated data reduction pipeline. In addition, a new photovoltaic array will supply most of the observatory's power. The LAT survey will cover about 60% of the sky at a regular observing cadence, with five times the angular resolution and ten times the map depth of the Planck satellite. The science goals are to: (1) determine the physical conditions in the early universe and constrain the existence of new light particles; (2) measure the integrated distribution of mass, electron pressure, and electron momentum in the late-time universe, and, in combination with optical surveys, determine the neutrino mass and the effects of dark energy via tomographic measurements of the growth of structure at redshifts z ≲ 3; (3) measure the distribution of electron density and pressure around galaxy groups and clusters, and calibrate the effects of energy input from galaxy formation on the surrounding environment; (4) produce a sample of more than 30,000 galaxy clusters, and more than 100,000 extragalactic millimeter sources, including regularly sampled AGN light-curves, to study these sources and their emission physics; (5) measure the polarized emission from magnetically aligned dust grains in our Galaxy, to study the properties of dust and the role of magnetic fields in star formation; (6) constrain asteroid regoliths, search for Trans-Neptunian Objects, and either detect or eliminate large portions of the phase space in the search for Planet 9; and (7) provide a powerful new window into the transient universe on time scales of minutes to years, concurrent with observations from the Vera C. Rubin Observatory of overlapping sky.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Energy conservation and the chiral magnetic effect

We analyze the chiral magnetic effect in a homogeneous neutral plasma from the point of view of energy conservation, and construct an effective potential for the growth of maximally helical perturbations of the electromagnetic field. We show that a negative curvature at the origin of the potential, indicating instability of the plasma, is induced by a chiral asymmetry in electron Fermi energy, as opposed to number density, while the potential grows at large field value. It follows that the ground state for a plasma has zero magnetic helicity; a nonzero electron mass will allow an excited state of a plasma with nonzero helicity to relax to that ground state quickly. We conclude that a chiral plasma instability triggered by weak interactions is not a viable mechanism for explaining magnetic fields in stars except possibly when dynamics drives the system far from equilibrium.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

SPT-3G+: mapping the high-frequency cosmic microwave background using kinetic inductance detectors

We present the design and science goals of SPT-3G+, a new camera for the South Pole Telescope, which will consist of a dense array of 34100 kinetic inductance detectors measuring the cosmic microwave background (CMB) at 220, 285 and 345 GHz. The SPT-3G+ dataset will enable new constraints on the process of reionization, including measurements of the patchy kinematic Sunyaev-Zeldovich effect and improved constraints on the optical depth due to reionization. At the same time, it will serve as a pathfinder for the detection of Rayleigh scattering, which could allow future CMB surveys to constrain cosmological parameters better than from the primary CMB alone. In addition, the combined, multi-band SPT-3G and SPT-3G+ survey data, will have several synergies that enhance the original SPT-3G survey, including: extending the redshift-reach of SZ cluster surveys to z > 2; understanding the relationship between magnetic fields and star formation in our Galaxy; improved characterization of the impact of dust on inflationary B-mode searches; and characterizing astrophysical transients at the boundary between mm and sub-mm wavelengths. Finally, the modular design of the SPT-3G+ camera allows it to serve as an on-sky demonstrator for new detector technologies employing microwave readout, such as the on-chip spectrometers that we expect to deploy during the SPT-3G+ survey. In this paper, we describe the science goals of the project and the key technology developments that enable its powerful yet compact design.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Exploring the Evolution of Stellar Rotation Using Galactic Kinematics

The rotational evolution of cool dwarfs is poorly constrained after ∼1–2 Gyr due to a lack of precise ages and rotation periods for old main-sequence stars. In this work, we use velocity dispersion as an age proxy to reveal the temperature-dependent rotational evolution of low-mass Kepler dwarfs and demonstrate that kinematic ages could be a useful tool for calibrating gyrochronology in the future. We find that a linear gyrochronology model, calibrated to fit the period–T{sub eff} relationship of the Praesepe cluster, does not apply to stars older than around 1 Gyr. Although late K dwarfs spin more slowly than early-K dwarfs when they are young, at old ages, we find that late K dwarfs rotate at the same rate or faster than early-K dwarfs of the same age. This result agrees qualitatively with semiempirical models that vary the rate of surface-to-core angular momentum transport as a function of time and mass. It also aligns with recent observations of stars in the NGC 6811 cluster, which indicate that the surface rotation rates of K dwarfs go through an epoch of inhibited evolution. We find that the oldest Kepler stars with measured rotation periods are late K and early M dwarfs, indicating that these stars maintain spotted surfaces and stay magnetically active longer than more massive stars. Finally, based on their kinematics, we confirm that many rapidly rotating GKM dwarfs are likely to be synchronized binaries.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Magnetic flux density from the relative circular motion of stars and partially ionized gas in the galaxy mid-plane vicinity

Observations suggest a slower stellar rotation relative to gas rotation in the outer part of the Milky Way Galaxy. This difference could be attributed to an interaction with the interstellar magnetic field. In a simple model, fields of order 10 μG are then required, consistently with the observed values. This coincidence suggests a tool for estimating magnetic fields in spiral galaxies. A north–south asymmetry in the rotation of gas in the Galaxy could be of magnetic origin too.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Trumpler 16-26: a new centrifugal magnetosphere star discovered via SDSS/APOGEE H -band spectroscopy

ABSTRACT We report the discovery of a new example of the rare class of highly magnetized, rapidly rotating, helium enhanced, early B stars that produce anomalously wide hydrogen emission due to a centrifugal magnetosphere (CM). The star is Trumpler 16-26, a B1.5 V member of the Trumpler 16 open cluster. A CM was initially suspected based on hydrogen Brackett series emission observed in SDSS/APOGEE H-band spectra. Similar to the other stars of this type, the emission was highly variable and at all times remarkable due to the extreme velocity separations of the double peaks (up to 1300 km s−1.) Another clue lay in the TESS light curve, which shows two irregular eclipses per cycle when phased with the likely 0.971 8115-d rotation period, similar to the behaviour of the well-known CM host star σ Ori E. To confirm a strong magnetic field and rotation-phase-locked variability, we initiated a follow-up campaign consisting of optical spectropolarimetry and spectroscopy. The associated data revealed a longitudinal magnetic field varying between −3.1 and +1.6 kG with the period found from photometry. The optical spectra confirmed rapid rotation (v sin i = 195 km s−1), surface helium enhancement, and wide, variable hydrogen emission. Tr16-26 is thus confirmed as the 20th known, the fourth most rapidly rotating, and the faintest CM host star yet discovered. With a projected dipole magnetic field strength of Bd > 11 kG, Tr16-26 is also among the most magnetic CM stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

1 Hz FLARING IN THE ACCRETING MILLISECOND PULSAR NGC 6440 X-2: DISK TRAPPING AND ACCRETION CYCLES

The dynamics of the plasma in the inner regions of an accretion disk around accreting millisecond X-ray pulsars (AMXPs) is controlled by the magnetic field of the neutron star. The interaction between an accretion disk and a strong magnetic field is not well understood, particularly at low accretion rates (the so-called propeller regime). This is due in part to the lack of clear observational diagnostics to constrain the physics of the disk-field interaction. Here, we associate the strong {approx}1 Hz modulation seen in the AMXP NGC 6440 X-2 with an instability that arises when the inner edge of the accretion disk is close to the corotation radius (where the stellar rotation rate matches the Keplerian speed in the disk). A similar modulation has previously been observed in another AMXP (SAX J1808.4-3658) and we suggest that the two phenomena are related and that this may be a common phenomenon among other magnetized systems. Detailed comparisons with theoretical models suggest that when the instability is observed, the interaction region between the disk and the field is very narrow-of the order of 1 km. Modeling further suggests that there is a transition region ({approx}1-10 km) around the corotation radius where the disk-field torque changes sign from spin-up to spin-down. This is the first time that a direct observational constraint has been placed on the width of the disk-magnetosphere interaction region, in the frame of the trapped-disk instability model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

CENSUS OF BLUE STARS IN SDSS DR8

We present a census of the 12,060 spectra of blue objects ((g – r){sub 0} < –0.25) in the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8). As part of the data release, all of the spectra were cross-correlated with 48 template spectra of stars, galaxies, and QSOs to determine the best match. We compared the blue spectra by eye to the templates assigned in SDSS DR8. 10,856 of the objects matched their assigned template, 170 could not be classified due to low signal-to-noise ratio, and 1034 were given new classifications. We identify 7458 DA white dwarfs, 1145 DB white dwarfs, 273 rarer white dwarfs (including carbon, DZ, DQ, and magnetic), 294 subdwarf O stars, 648 subdwarf B stars, 679 blue horizontal branch stars, 1026 blue stragglers, 13 cataclysmic variables, 129 white dwarf-M dwarf binaries, 36 objects with spectra similar to DO white dwarfs, 179, quasi-stellar objects (QSOs), and 10 galaxies. We provide two tables of these objects, sample spectra that match the templates, figures showing all of the spectra that were grouped by eye, and diagnostic plots that show the positions, colors, apparent magnitudes, proper motions, etc., for each classification. Future surveys will be able to use templates similar to stars in each of the classes we identify to automatically classify blue stars, including rare types.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Magnetic Inflation and Stellar Mass. I. Revised Parameters for the Component Stars of the Kepler Low-mass Eclipsing Binary T-Cyg1-12664

Several low-mass eclipsing binary stars show larger than expected radii for their measured mass, metallicity, and age. One proposed mechanism for this radius inflation involves inhibited internal convection and starspots caused by strong magnetic fields. One particular eclipsing binary, T-Cyg1-12664, has proven confounding to this scenario. Çakırlı et al. measured a radius for the secondary component that is twice as large as model predictions for stars with the same mass and age, but a primary mass that is consistent with predictions. Iglesias-Marzoa et al. independently measured the radii and masses of the component stars and found that the radius of the secondary is not in fact inflated with respect to models, but that the primary is, which is consistent with the inhibited convection scenario. However, in their mass determinations, Iglesias-Marzoa et al. lacked independent radial velocity measurements for the secondary component due to the star’s faintness at optical wavelengths. The secondary component is especially interesting, as its purported mass is near the transition from partially convective to a fully convective interior. In this article, we independently determined the masses and radii of the component stars of T-Cyg1-12664 using archival Kepler data and radial velocity measurements of both component stars obtained with IGRINS on the Discovery Channel Telescope and NIRSPEC and HIRES on the Keck Telescopes. We show that neither of the component stars is inflated with respect to models. Our results are broadly consistent with modern stellar evolutionary models for main-sequence M dwarf stars and do not require inhibited convection by magnetic fields to account for the stellar radii.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Magnetosphere Evolution and Precursor-driven Electromagnetic Signals in Merging Binary Neutron Stars

We detail new force-free simulations to investigate magnetosphere evolution and precursor electromagnetic (EM) signals from binary neutron stars. Our simulations fully follow a representative inspiral motion, capturing the intricate magnetospheric dynamics and their impact on EM outflows. We explore a range of stellar magnetic moment orientations and relative strengths, finding that the magnetospheres and Poynting flux evolution are strongly configuration dependent. The Poynting flux exhibits pulsations at twice the orbital frequency, 2Ω, and is highly anisotropic, following a power-law dependence on orbital frequency. The index ranges from 1 to 6, shaped by the intricate dynamics of the magnetospheres. Furthermore, we present the first computation of (1) the EM forces acting on the star surfaces, revealing the presence of torques that, for highly magnetized stars, could influence the orbital dynamics or break the crust; (2) the high-energy emission signals from these systems by adopting the established isolated pulsar theory. Assuming curvature radiation in the radiation-reaction limit, we find that photons could reach TeV–PeV energies in the last ∼ms for magnetic field strengths 10 10 –10 15 G. However, our analysis of single photon magnetic pair production suggests that these photons are unlikely to escape, with the MeV band emerging as a promising observational window for precursor high-energy emission. In this framework, we construct high-energy emission skymaps and light curves, exploring observational implications. Finally, we propose potential precursor radio emission and delayed afterglow echoes from magnetized outflows, which may contribute to late-time rebrightening in short gamma-ray bursts or to orphan afterglows.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

ENIGMAS FROM THE SLOAN DIGITAL SKY SURVEY DR7 KLEINMAN WHITE DWARF CATALOG

We report results from a continuation of our searches for high field magnetic white dwarfs (WDs) paired in a detached binary with non-degenerate companions. We made use of the Sloan Digital Sky Survey DR7 catalog of Kleinman et al. (2013) with 19,712 spectroscopically identified WDs. These include 1735 WD plus M dwarf detached pairs (almost 10% of the Kleinman et al.'s list). No new pairs were found, although we did recover the polar (AM Herculis system) ST LMi in a low state of accretion. With the larger sample the original situation reported 10 yr ago remains intact now at a much higher level of statistical significance: in the selected SDSS sample, high field magnetic WDs are not found in an apparently detached pairing with an M dwarf, unless they are a magnetic cataclysmic variable (CV) in a low state of accretion. This finding strengthens the case that the fields in the isolated high field magnetic WDs are generated by stellar mergers but also raises questions on the nature of the progenitors of the magnetic CVs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

DISSECTING MAGNETAR VARIABILITY WITH BAYESIAN HIERARCHICAL MODELS

Neutron stars are a prime laboratory for testing physical processes under conditions of strong gravity, high density, and extreme magnetic fields. Among the zoo of neutron star phenomena, magnetars stand out for their bursting behavior, ranging from extremely bright, rare giant flares to numerous, less energetic recurrent bursts. The exact trigger and emission mechanisms for these bursts are not known; favored models involve either a crust fracture and subsequent energy release into the magnetosphere, or explosive reconnection of magnetic field lines. In the absence of a predictive model, understanding the physical processes responsible for magnetar burst variability is difficult. Here, we develop an empirical model that decomposes magnetar bursts into a superposition of small spike-like features with a simple functional form, where the number of model components is itself part of the inference problem. The cascades of spikes that we model might be formed by avalanches of reconnection, or crust rupture aftershocks. Using Markov Chain Monte Carlo sampling augmented with reversible jumps between models with different numbers of parameters, we characterize the posterior distributions of the model parameters and the number of components per burst. We relate these model parameters to physical quantities in the system, and show for the first time that the variability within a burst does not conform to predictions from ideas of self-organized criticality. We also examine how well the properties of the spikes fit the predictions of simplified cascade models for the different trigger mechanisms.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Gamma-ray timing of redback PSR J2339–0533: Hints for gravitational quadrupole moment changes

We present the results of precision gamma-ray timing measurements of the binary millisecond pulsar PSR J2339–0533, an irradiating system of the “redback” type, using data from the Fermi Large Area Telescope. We describe an optimized analysis method to determine a long-term phase-coherent timing solution spanning more than six years, including a measured eccentricity of the binary orbit and constraints on the proper motion of the system. A major result of this timing analysis is the discovery of an extreme variation of the nominal 4.6 hr orbital period P{sub orb} over time, showing alternating epochs of decrease and increase. We inferred a cyclic modulation of P{sub orb} with an approximate cycle duration of 4.2 yr and a modulation amplitude of ΔP{sub orb}/P{sub orb}=2.3×10{sup −7}. Considering different possible physical causes, the observed orbital-period modulation most likely results from a variable gravitational quadrupole moment of the companion star due to cyclic magnetic activity in its convective zone.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Search for axions from magnetic white dwarfs with Chandra x-ray observations

Low-mass axionlike particles could be produced in abundance within the cores of hot, compact magnetic white dwarf (MWD) stars from electron bremsstrahlung and converted to detectable x-rays in the strong magnetic fields surrounding these systems. In this work, we constrain the existence of such axions from two dedicated Chandra x-ray observations of ∼ 40 ks each in the energy range ∼ 1–10 keV toward the MWDs WD 1859 +148 and PG 0945 + 246. We find no evidence for axions, which constrains the axion-electron times axion-photon coupling to |𝑔 𝑎⁢𝛾⁢𝛾 ⁡𝑔 𝑎⁢𝑒⁢𝑒 | ≲ 1.54 ×10 −25 (3.54 × 10 −25 ) GeV −1 for PG 0945 + 246 (WD 1859 +148) at 95% confidence for axion masses 𝑚 𝑎 ≲ 10 −6 eV. Here, we find an excess of low-energy x-rays between 1 and 3 keV for WD 1859 + 148 but determine that the spectral morphology is too soft to arise from axions; instead, the soft x-rays may arise from nonthermal emission in the MWD magnetosphere.

Axions↗
DOE OSTI2017

Effect of angular momentum alignment and strong magnetic fields on the formation of protostellar discs

Star-forming molecular clouds are observed to be both highly magnetized and turbulent. Consequently, the formation of protostellar discs is largely dependent on the complex interaction between gravity, magnetic fields, and turbulence. Studies of non-turbulent protostellar disc formation with realistic magnetic fields have shown that these fields are efficient in removing angular momentum from the forming discs, preventing their formation. However, once turbulence is included, discs can form in even highly magnetized clouds, although the precise mechanism remains uncertain. In this work, we introduce several high-resolution simulations of turbulent, realistically magnetized, high-mass molecular clouds with both aligned and random turbulence to study the role that turbulence, misalignment, and magnetic fields have on the formation of protostellar discs. We reveal that when the turbulence is artificially aligned so that the angular momentum is parallel to the initial uniform field, no rotationally supported discs are formed, regardless of the initial turbulent energy. We conclude that turbulence and the associated misalignment between the angular momentum and the magnetic field are crucial in the formation of protostellar discs in the presence of realistic magnetic fields.

79 ASTRONOMY AND ASTROPHYSICS↗