Blackbody Spectrum Research Articles

Black-body radiation in an accelerated frame

We derive Planck’s radiation law in a uniformly accelerated frame expressed in Rindler coordinates. The black-body spectrum is time-dependent in its temperature and Planckian at each instantaneous time, but it is scaled by an emissivity factor that depends on the Rindler spatial coordinate and the acceleration magnitude. An observer in an accelerated frame will perceive the black-body as black, hyperblack, or grey, depending on their position relative to the source (moving away or toward it), the acceleration magnitude, and whether they are accelerating or decelerating. For an observer accelerating away from the source, there exists a threshold on the acceleration magnitude beyond which they no longer receive radiation from the black-body. Since the frequency and the number of modes in Planck’s law evolve over time, the spectrum is continuously red- or blue-shifted towards lower or higher frequencies as time progresses, and the radiation modes (photons) may be created or annihilated, depending on the observer’s position and their acceleration or deceleration relative to the source of radiation.

Investigation of Energy Deposition by Soft X-rays into Solar Cell Materials

A high-altitude nuclear detonation releases a significant portion of energy as X-rays with a blackbody spectrum. Satellites are particularly vulnerable to prompt soft X-rays (~1 keV) absorbed within a few microns of the surface of the solar array, causing melting and evaporation of its materials. The absorption of soft X-rays in solar cell materials is studied using GEANT4 computer software. Energy deposition as a function of depth (depth-dose profile) is calculated for slab geometries of dielectric and metallic materials. The photo-absorption and Compton scattering of X-rays and the contribution of secondary radiation, such as photo-electrons, Auger-electrons, and fluorescence photons are taken into account. The effect of the production of secondary radiation on the distribution of deposited dose in the near-surface region of materials is investigated. The results presented in this work are validated against published data and provide valuable insights into X-ray absorption by solar cell materials, the redistribution of energy by secondary radiation, and the spatial scale of power density deposition that can be used as a source term for the further thermomechanical analysis of a material’s phase transformations and melting.

Performance evaluation of thin film GaSb thermophotovoltaic cells

Economical converters are the key component for the industrial applications of thermophotovoltaic technology. In this work thin film GaSb cells are demonstrated for broadband thermophotovoltaic energy conversion. It is shown that n-on-p configuration is a superior choice for thin film cell due to its larger accessible efficiency. Under the illumination of unshaped blackbody spectrum, the matched spectrum temperature for GaSb thin film cells should be in the range of 2000∼2600 K, With those matched spectra, the optimal GaSb thin film can achieve the efficiency up to 8% or so with V OC = 0.55 V, FF = 0.64, J SC = 44 A cm−2, thus showing the power density output up to 15 W cm−2 while only having the active layer thickness 4.5 μm or so. These results are well preserved for S F no more than 104 cm s−1. With increasing spectrum temperature, a phenomenological model has also been formulated to analytically predict the optimal cell structure at a given spectrum illumination. This work has thus established the fundamental guidelines to develop GaSb thin film cells or subcells for economical thermophotovoltaic energy conversion.

Optically Quiet, But FUV Loud: Results from comparing the far-ultraviolet predictions of flare models with TESS and HST

Abstract The far-ultraviolet (FUV) flare activity of low-mass stars has become a focus in our understanding of the exoplanet atmospheres and how they evolve. However, direct detection of FUV flares and measurements of their energies and rates are limited by the need for space-based observations. The difficulty of obtaining such observations may push some works to use widely available optical data to calibrate multi-wavelength spectral models that describe UV and optical flare emission. These models either use single temperature blackbody curves to describe this emission, or combine a blackbody curve with archival spectra. These calibrated models would then be used to predict the FUV flare rates of low-mass stars of interest. To aid these works, we used TESS optical photometry and archival HST FUV spectroscopy to test the FUV predictions of literature flare models. We tested models for partially (M0-M2) and fully convective (M4-M5) stars, 40 Myr and field age stars, and optically quiet stars. We calculated FUV energy correction factors that can be used to bring the FUV predictions of tested models in line with observations. A flare model combining optical and NUV blackbody emission with FUV emission based on HST observations provided the best estimate of FUV flare activity, where others underestimated the emission at all ages, masses and activity levels, by up to a factor of 104 for combined FUV continuum and line emission and greater for individual emission lines. We also confirmed previous findings that showed optically quiet low-mass stars exhibit regular FUV flares.

Inflationary initial conditions for the cosmological gravitational wave background

The initial conditions on the anisotropies of the stochastic gravitational-wave background of cosmological origin (CGWB) largely depend on the mechanism that generates the gravitational waves. Since the CGWB is expected to be non-thermal, the computation of the initial conditions could be more challenging w.r.t. the Cosmic Microwave Background (CMB), whose interactions with other particles in the early Universe lead to a blackbody spectrum. In this paper, we show that the initial conditions for the cosmological background generated by quantum fluctuations of the metric during inflation deviate from adiabaticity. These primordial gravitational waves are indeed generated by quantum fluctuations of two independent degrees of freedom (the two polarization states of the gravitons). Furthermore, the CGWB plays a negligible role in the Einstein's equations, because its energy density is subdominant w.r.t. ordinary matter. Therefore, the only possible way to compute the initial conditions for inflationary gravitons is to perturb the energy-momentum tensor of the gravitational field defined in term of the small-scale tensor perturbation of the metric. This new and self-consistent approach shows that a large, non-adiabatic initial condition is present even during the single-field inflation. Such a contribution enhances the total angular power spectrum of the CGWB compared to the standard adiabatic case, increasing also the sensitivity of the anisotropies to the presence of relativistic and decoupled particles in the early Universe. In this work we have also proved that our findings are quite general and apply to both single-field inflation and other scenarios in which the CGWB is generated by the quantum fluctuations of the metric, like the curvaton.

Determination of the temperature of an object irradiated by microwaves using spectral pyrometry

Recently, due to increasing environmental requirements, microwave carbonization method has been widely investigated for the production of activated carbon from biomass waste. Microwave carbonization is a more energy efficient and environmentally friendly method compared to traditional carbonization in thermal furnaces, but to date there are still a number of questions about the reproducibility and temperature stability of this process. During microwave irradiation, the temperature of biomass samples changes continuously and complex physical and chemical processes occur in them. For deeper study of these processes and determination of optimal modes of microwave treatment it is necessary to know the temperature dynamics of biomass samples. For this purpose, the method of spectral pyrometry based on the allocation of sections of the spectra of thermal radiation of samples coinciding with the Planck spectrum was used. In the specified spectral sections these samples are gray emitters. The method is effective for an unknown emission coefficient, continuously varying with changes in the microstructure, chemical composition and phase state of the sample. The sample irradiated by microwaves was a sample of orthophosphoric acid-treated cotton down weighing 1 g. The microwave source was a magnetron-type generator with a maximum output power of 600 W and an operating frequency of 2450 MHz. Thermal spectra of the irradiated sample were recorded by small-size spectrometers of visible (350–760 nm) and near-infrared (650–1050 nm) ranges. The time of irradiation of samples by microwaves was varied in the range of 60–180 s. To process the obtained spectra, the program “Spectral Pyrometry” was used, which reads the recorded spectrum, processes it, plots it in the necessary coordinates and calculates the temperature. Analysis of the obtained results revealed different types of thermal radiation spectra of the irradiated sample - spectra similar to spectra of a completely black body, spectra with different temperature zones of the sample, spectra with atomic lines and molecular bands. The results obtained are useful for the study of microwave influence on various objects, research of processes occurring during carbonization of biomass, as well as for the development of more effective modes of production of activated carbons by microwave method.

The bright black hole X-ray binary 4U 1543-47 during 2021 outburst. A clear state transition from super-Eddington to sub-Eddington accretion revealed by Insight-HXMT

ABSTRACT We present a detailed analysis of the observations with the Hard X-ray Modulation Telescope of the black hole X-ray transient 4U 1543-47 during its outburst in 2021. We find a clear state transition during the outburst decay of the source. Using previous measurements of the black hole mass and distance to the source, the source luminosity during this transition is close to the Eddington limit. The light curves before and after the transition can be fitted by two exponential functions with short (∼16 d) and long (∼130 d) decay time-scales, respectively. We detect strong reflection features in all observations that can be described with either the relxillns or reflionx_bb reflection models, both of which have a black-body incident spectrum. In the super-Eddington state, we observe a Comptonized component characterized by a low electron temperature of approximately 2.0 keV. We suggest that this component appears exclusively within the inner radiation-pressure-dominated region of the supercritical disc as a part of the intrinsic spectrum of the accretion disc itself. This feature vanishes as the source transitions into the sub-Eddington state. The emissivity index of the accretion disc in the reflection component is significantly different before and after the transition, ∼3.0–5.0 and ∼7.0–9.0 in the super- and sub-Eddington states, respectively. Based on the reflection geometry of returning disc radiation, the geometrically thicker the accretion disc, the smaller the emissivity index. Therefore, we propose that the transition is primarily driven by the change of the accretion flow from a supercritical to a thin disc configuration.

Laser-type cooling with unfiltered sunlight.

Cooling of systems to sub-Kelvin temperatures is usually done using either a cold bath of particles or spontaneous photon scattering from a laser field; in either case, cooling is driven by interaction with a well-ordered cold (i.e., low-entropy) system. However, there have recently been several schemes proposed for "cooling by heating," in which raising the temperature of some mode drives the cooling of the desired system faster. We discuss how to cool a trapped ion to its motional ground state using unfiltered sunlight at 5800K to drive the cooling. We show how to treat the statistics of thermal light in a single-mode fiber for delivery to the ion and show experimentally how the blackbody spectrum is strongly modified by being embedded in quasi-one-dimension. Quantitative estimates for the achievable cooling rate with our measured fiber-coupled low-dimensional sunlight show promise for demonstrating this implementation of cooling by heating.

The 3D geometry of reflection nebulae IC 59 and IC 63 with their illuminating star gamma Cas

ABSTRACT The early-type star gamma Cas illuminates the reflection nebulae IC 59 and IC 63, creating two photodissociation regions (PDRs). Uncertainties about the distances to the nebulae and the resulting uncertainty about the density of the radiation fields incident on their surfaces have hampered the study of these PDRs during the past three decades. We employed far-ultraviolet (UV) – optical nebula – star colour differences of dust-scattered light to infer the locations of the nebulae relative to the plane of the sky containing gamma Cas, finding IC 63 to be positioned behind the star and IC 59 in front of the star. To obtain the linear distances of the nebulae relative to gamma Cas, we fit far-infrared archival Herschel flux data for IC 59 and IC 63 with modified blackbody curves and relate the resulting dust temperatures with the luminosity of gamma Cas, yielding approximate distances of 4.15 pc for IC 59 and 2.3 pc for IC 63. With these distances, using updated far-UV flux data in the 6–13.6 eV range for gamma Cas with two recent determinations of the interstellar extinction for gamma Cas, we estimate that the far-UV radiation density at the surface of IC 63 takes on values of G0 = 58 or G0 = 38 with respective values for E(B − V) for gamma Cas of 0.08 and 0.04 mag. This is a substantial reduction from the range 150 ≤ G0 ≤ 650 used for IC 63 during the past three decades. The corresponding, even lower new values for IC 59 are G0 = 18 and G0 = 12.

The magnetar crustal magneto‐thermal evolution

AbstractMagnetars are a type of pulsars powered by magnetic field energy. Part of the X‐ray luminosities of magnetars in quiescence have a thermal origin and can be fitted by a blackbody spectrum with the surface temperature, much higher than the typical values for rotation‐powered pulsars. The persistent thermal emissions and bursts of magnetars indicate the presence of some internal heat sources in their outer crusts. In this work, we have formulated the energy balance equation and applied it to investigate the thermal evolution in the magnetar crust, taking into account the heating mechanisms of Ohmic decay and electron capture processes. This model can explain the changes in the X‐ray luminosity of the magnetars.

Hydrogen recombination continuum as the radiative model for stellar optical flares

ABSTRACT The study of stellar flares has increased with new observations from CoRoT, Kepler, and TESS satellites, revealing the broad-band visible emission from these events. Typically, stellar flares have been modelled as 104 K blackbody plasma to obtain estimates of their total energy. In the Sun, white-light flares (WLFs) are much fainter than their stellar counterparts, and normally can only be detected via spatially resolved observations. Identifying the radiation mechanism for the formation of the visible spectrum from solar and stellar flares is crucial to understand the energy transfer processes during these events, but spectral data for WLFs are relatively rare, and insufficient to remove the ambiguity of their origin: photospheric blackbody radiation and/or Paschen continuum from hydrogen recombination in the chromosphere. We employed an analytical solution for the recombination continuum of hydrogen instead of the typically assumed 104 K blackbody spectrum to study the energy of stellar flares and infer their fractional area coverage. We investigated 37 events from Kepler-411 and five events from Kepler-396, using both radiation mechanisms. We find that estimates for the total flare energy from the H recombination spectrum are about an order of magnitude lower than the values obtained from the blackbody radiation. Given the known energy transfer processes in flares, we argue that the former is a physically more plausible model than the latter to explain the origin of the broad-band optical emission from flares.

Accelerated electron thermometer: observation of 1D Planck radiation

Abstract We report on the observation of thermal photons from an accelerated electron via examination of radiative beta decay of free neutrons measured by the RDK II collaboration. The emitted photon spectrum is shown to corroborate a thermal distribution consistent with the dynamical Casimir effect. Supported by a robust chi-squared statistic, we find the photons reside in a 1D Planck spectrum with a temperature predicted by the moving mirror model. Subject Indices: B50 (Electromagnetic processes and properties), D29 (Nuclear decays and radioactivities (including fission)), and E76 (Quantum field theory on curved space)

The Frayer Model as Analysis of Instruction and Student Knowledge in Undergraduate Astronomy

The American public’s factual knowledge about science has remained relatively unchanged over the past two decades. Research on scientific literacy connects to science education, interactive instruction techniques, and how introductory undergraduate science courses are many students’ last formal exposure to science. This highlights a need for research on how these courses can contribute toward a scientifically-literate citizenry. This study qualitatively analyzes how instruction in an introductory undergraduate astronomy course informs students on an astronomy concept, specifically blackbody radiation. A case study method of thematic analysis was employed by administering a pre- and post-lesson Frayer Model to students in an ASTR 1010 section and recording the professor’s lecture. Thematic analysis was conducted on all Frayer Models and the lecture transcript. Three key themes (refined understanding, blackbody spectrum, and ideal physical body) emerged, summarizing how students’ knowledge changed following instruction. The results section contextualizes these themes within how the concepts were taught. Blackbody radiation was entirely foreign to most students. Students utilized a few keywords, such as “perfect absorber,” to describe blackbodies. Their visual comprehension improved, for they accurately drew and labeled blackbody spectra. This study is novel in using the Frayer Model as an assessment tool in astronomy education research. The findings contextualize scientific literacy and nuance our understanding of how students conceptualize lecture-based instruction. Educators can interpret the results when considering how to teach blackbody radiation. Implications are made to a growing body of knowledge on language in astronomy education.

A Better Candidate for Dark Matter is Cosmic Plasma

In the ΛCDM cosmological model, based on observations of supernovae Ia, the cosmic dark energy density is assumed to be ΩΛ ∼ 0.70 and the gravitational mass density is assumed to be Ω m ∼ 0.30. Based on the assumption that the observed cosmic microwave background (CMB) is a thermal relic of the early hot universe, the cosmic plasma density should be small, i.e., Ω b ∼ 0.05 (otherwise the Sunyaev-Zeldovich effect of the cosmic plasma would ruin the observed CMB's perfect blackbody spectrum). To fill the gap between Ω m and Ω b , non-baryonic dark matter Ω c ∼ 0.25 is introduced into the ΛCDM model. If the CMB is the result of a partial thermal equilibrium between cosmic radiation and cosmic plasma, then the observed perfect blackbody spectrum of the CMB can coexist with cosmic plasma. In this case, it is not necessary to introduce non-baryonic cold dark matter into cosmological models. A better candidate for dark matter is the cosmic plasma.

Incandescent temporal metamaterials

Regarded as a promising alternative to spatially shaping matter, time-varying media can be seized to control and manipulate wave phenomena, including thermal radiation. Here, based upon the framework of macroscopic quantum electrodynamics, we elaborate a comprehensive quantum theoretical formulation that lies the basis for investigating thermal emission effects in time-modulated media. Our theory unveils unique physical features brought about by time-varying media: nontrivial correlations between fluctuating electromagnetic currents at different frequencies and positions, thermal radiation overcoming the black-body spectrum, and quantum vacuum amplification effects at finite temperature. We illustrate how these features lead to striking phenomena and innovative thermal emitters, specifically, showing that the time-modulation releases strong field fluctuations confined within epsilon-near-zero (ENZ) bodies, and that, in turn, it enables a narrowband (partially coherent) emission spanning the whole range of wavevectors, from near to far-field regimes.

An Energetic Eruption With Associated SO 1.707 Micron Emissions at Io's Kanehekili Fluctus and a Brightening Event at Loki Patera Observed by JWST

AbstractWe observed Io with the James Webb Space Telescope (JWST) while the satellite was in eclipse, and detected thermal emission from several volcanoes. The data were taken as part of our JWST‐ERS program #1373 on 15 November 2022. Kanehekili Fluctus was exceptionally bright, and Loki Patera had most likely entered a new brightening phase. Spectra were taken with NIRSpec/IFU at a resolving power R ≈ 2,700 between 1.65 and 5.3 µm. The spectra were matched by a combination of blackbody curves that showed that the highest temperature, ∼1,200 K, for Kanehekili Fluctus originated from an area ∼0.25 km2 in size, and for Loki Patera this high temperature was confined to an area of ∼0.06 km2. Lower temperatures, down to 300 K, cover areas of ∼2,000 km2 for Kanehekili Fluctus, and ∼5,000 km2 for Loki Patera. We further detected the a1Δ ⇒ X3Σ− 1.707 µm rovibronic forbidden SO emission band complex over the southern hemisphere, which peaked at the location of Kanehekili Fluctus. This is the first time this emission has been seen above an active volcano, and suggests that the origin of such emissions is ejection of SO molecules directly from the vent in an excited state, after having been equilibrated at temperatures of ∼1,500 K below the surface, as was previously hypothesized.

Emission spectra of fullerenes: Computational evidence for blackbody-like radiation due to structural diversity and electronic similarity

The spectral emission of hot ${\mathrm{C}}_{60}$ has been experimentally shown to be broad and continuous, in apparent contradiction with the discrete and narrow absorption spectrum associated with the high symmetry of buckminsterfullerene. In the present work we computationally model the emission spectrum of isolated carbon clusters, assuming a broad distribution of isomers that are likely populated under the experimental conditions. The contributions of individual structures to the global spectrum correspond to the relaxation via recurrent fluorescence and vibrational emission, electronic and vibrational structures being described by a simple but efficient density-functional-based tight-binding scheme. The model predicts a blackbody-like emission spectrum that is naturally broad and correctly accounts for the experimental measurements, except for a maximum that is quantitatively shifted with respect to Wien's displacement law. To quantify such differences, we introduce an emissivity parameter $\ensuremath{\varepsilon}$ as the ratio between the spectral emittance and the corresponding exact blackbody spectrum; $\ensuremath{\varepsilon}$ is numerically found to scale as ${(\ensuremath{\lambda}T)}^{\ensuremath{-}2}$ at leading order with increasing temperature $T$ and for wavelengths $\ensuremath{\lambda}>350$ nm, and we provide a theoretical justification for this behavior. Our results are discussed in the light of the astrophysical detection of interstellar fullerenes, as well as in combustion environments where carbon clusters are relevant in the context of nascent soot particle formation.

Arthur E. Haas, from the Atom to the Cosmos—Struggles for a Scientific Career in the Early 20th Century

Arthur E. Haas, from the Atom to the Cosmos—Struggles for a Scientific Career in the Early 20th Century

TRIPLE MULTIPLICATIVE THERMORESONANCES ON THE SPECTRA OF EXCHANGE INERTIAL RADIATION GENERATED IN NON-EQUILIBRIUM MEDIA WITH CONTACT GAPS IN ENGINEERING, COSMIC, PSEUDO-ELEMENTARY AND BIOLOGICAL SYSTEMS IN COMPLEX SPACE WITH TRIPLET VIOLATION OF ANTISYMMETRY

Calculated ratios that quantitatively describe the properties of resonance triplets of inertial radiation generated in non-equilibrium systems of various scales and levels of organization are given. The multiplicative nature of the energy of resonant components is revealed, which is significantly different from the additive principles of the formation of known triplet structures. The mechanism of triplet violation of the antisymmetry of the complex space is established, which ensures the avoidance of annihilation of the energy created according to the principle of Creatio ex nihilo in the topological contact gaps between the real and imaginary half-spaces. There is a marked dilution of the dominant energy cascades – direct in the imaginary and inverted in the real half-space. The analysis of resonant triads on nuclear and collider spectra was carried out, the components of these spectra were explained and quantitatively calculated. The muon structure of hadrons was confirmed and the parameters of this structure were calculated, as well as the parameters of the collider proton-muon plasma, alternative to the known models of the quark-gluon plasma. The calculation of the spectra of cosmic rays of low, medium, high and ultra-high energies was made, which quantitatively corresponds to natural data. Triple resonances in the spectra of the Sun’s radiation and the spectra of solar and geomagnetic activity were detected and quantified. It is shown that the solar spectrum is significantly different from the blackbody spectrum, and the main periods of the Sun’s activity are determined by resonant triads on the scale of the heliosphere. Calculated parameters of the cold outer photosphere at the periphery of the Solar System, the background microwave radiation of which is usually erroneously attributed to the account of a “relic” from the so-called Big bang. The analysis of resonant triplets on the spectra of acoustic disturbances in technical systems was carried out. Synchronization of gravitational and electromagnetic modes is noted, which leads to dangerous buffeting modes. The relationship between geodynamic, climatic and biological processes on the planet and the activity of cavitation topological gaps on the periphery of the Solar System has been established. The mechanism of contact capillary thermostabilization of the human body was revealed and the multiplicative triplet coronavirus destruction of this mechanism was noted.

Nonlinearity Correction of Fourier Transform Spectrometer in Solar Observation Using Simulated Annealing

A Fourier transform spectrometer (FTS) has been used to observe solar activities due to its ultra-high spectral resolution. However, the FTS in-band spectra are usually distorted and some artifacts appear in out-of-band regions due to nonlinear effects. Therefore, the FTS nonlinear problem must be corrected. In this study, we proposed a novel method to correct the nonlinear effects using simulated annealing. We simulated several nonlinear spectra to evaluate the performance of our method. The calculated quadratic coefficients are extremely close to the given values, demonstrating that the method is effective and accurate. The proposed method is further used to correct the blackbody and solar spectra with nonlinearity obtained by Bruker IFS-125HR installed at the Huairou Solar Observing Station, which is a pathfinder for the accurate infrared magnetic field measurements of the Sun project. To the blackbody spectra, the nonlinearity in low- and high-frequency regions are corrected by 89.09% and 60.84%. The nonlinear correction of the solar spectra in the low- and high-frequency regions have reached 65.34% and 81.04%, respectively. These results prove that our method can correct the nonlinear problem to improve the data accuracy.