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DOE OSTI2024

The universal thermodynamic properties of extremely compact objects

An extremely compact object (ECO) is defined as a quantum object without horizon, whose radius is just a small distance s outside its Schwarzschild radius. We show that any ECO of mass M in d + 1 dimensions with s << (M/m p ) 2/(d-2)(d+1) lp must have (at leading order) the same thermodynamic properties—temperature, entropy and radiation rates—as the corresponding semiclassical black hole of mass M. An essential aspect of the argument involves showing that the Tolman–Oppenheimer–Volkoff equation has no consistent solution in the region just outside the ECO surface, unless this region is filled with radiation at the (appropriately blueshifted) Hawking temperature. In string theory it has been found that black hole microstates are fuzzballs—objects with no horizon—which are expected to have a radius that is only a little larger than the horizon radius. Thus the arguments of this paper provide a nice closure to the fuzzball paradigm: the absence of a horizon removes the information paradox, and the thermodynamic properties of the semiclassical hole are nonetheless recovered to an excellent approximation.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1992

Radiation dynamics in X-ray binaries. I - Type 1 bursts. II - Type 2 bursts. III - Extremely compact objects

Equations describing the evolution of a thin, axisymmetric, viscous, relativistic, irradiated accretion disk are presented, as well as numerical solutions of these equations in the case where irradiation results from a thermonuclear flash on the surface of the accreting neutron star. These calculations verify the notion that the radiation torque induces a substantial increase in the accretion rate, during a type 1 X-ray burst, and provide insight into the factors which influence the dynamical response of the disk. A new model for the source XBT 1730-335, the rapid burster, is presented. Temporal and spectral properties are calculated. The rapid burster is found to be a nonmagnetic, 'critically compact', slowly rotating neutron star in a highly eccentric binary system with a period of 6 mo. The spectral modifications which arise from the scattering of photons by accretion disks around nonmagnetic neutron stars are calculated. The 'black hole candidates' are interpreted as extremely compact stars.

Walker, Mark A.↗

DOE OSTI2023

The universality of black hole thermodynamics

The thermodynamic properties of black holes — temperature, entropy and radiation rates — are usually associated with the presence of a horizon. We argue that any extremely compact object (ECO) must have the same thermodynamic properties. Here, quantum fields just outside the surface of an ECO have a large negative Casimir energy similar to the Boulware vacuum of black holes. If the thermal radiation emanating from the ECO does not fill the near-surface region at the local Unruh temperature, then we find that no solution of gravity equations is possible. In string theory, black holes microstates are horizonless quantum objects called fuzzballs that are expected to have a surface ~l p outside r = 2⁢GM; thus the information puzzle is resolved while preserving the semiclassical thermodynamics of black holes.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

Novel Signatures Beyond the Standard Model: From Extreme Environments to Precision Measurements

Most of our universe is dark. It is dark literally—visible matter makes up only 5% of the energy density—and conceptually, as many outstanding questions remain unsolved. The discovery of particle dark matter would shed light on our dark universe and throw open a window on the highest energy scales. This research made progress toward dark matter and new particle searches in three ways. Extreme compact objects, such as black holes, neutron stars, and stellar cores, can parametrically increase the production rates of feebly interacting particles and yield observable signatures. Specifically, a process known as superradiance leads to exponential growth of the number of ultralight particles gravitationally bound to rotating black holes, and turns astrophysical black holes into particle detectors. This research broadened the scope of applicability of superradiance studies to particles with a wide range of interactions and masses, predicting multi messenger signals. When ultralight particles are produced as dark matter in the early universe, they can be detected directly in laboratory experiments. However, these feebly interacting particles lead to small signals that are inevitably difficult to tease out from backgrounds; their detection requires the theoretical development of unique signatures that can be searched for in low-noise experiments. Some dark matter particles could be detectable with thin film metamaterials combined with low noise single-photon detectors. This research develop the theoretical framework and supported experimental efforts for ambitious searches for a wider class of ultralight particles. Overall, the outcome of this theoretical particle physics program developed novel signatures of new dark matter particles, and thereby expanded the particle parameter space which can be explored with astrophysical observations and precision experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1978

The X-ray structure of NGC 5128

During an observation of NGC 5128 (Cen A) by the rotating modulation collimator on board the SAS-3 X-ray observatory in early June 1975, data were obtained which suggest the presence of an extended source with about 3 arcmin FWHM surrounding an extremely compact object located at the radio/IR nucleus. The point component exhibited a 25% increase in intensity over a period of 2 to 5 hours.

Delvaille, J. P.↗

NASA NTRS1981

Extremely red compact radio sources - The empty field objects

Radiation of 10 microns has been detected from 1413+135, one of the very red objects discovered by Rieke, Lebofsky, and Kinman (1979) at near-infrared wavelengths. The spectrum of this object flattens at wavelengths longer than 2.2 microns. Upper limits are also given for the 10-micron emission from 2255+14, 0026+34, and 0406+121. Photometry between 1.25 and 2.2 microns confirms the variability of 1413+135, 2255+41, and 0406+121. Five percent resolution spectra of 1413+135 and 0406+121 between 1.5 and 2.4 microns show no emission or absorption lines. The spectral data rule out the possibility that 1413+135 is a quasar with normal line strengths and a redshift less than 1.3 and greater than 4. The lack of features of the 1.5-2.4-micron spectra, the rapid variability, and the overall shape of the radio, infrared, and X-ray energy distributions are consistent with a BL Lac nature for these objects.

Beichman, C. A.↗

NASA NTRS1978

X-ray and radio emission from the compact galaxy III Zw 2

X-rays from the compact galaxy III Zw 2 have been detected with the rotating modulation collimator on board SAS 3. The (2-10-keV) flux is (4.3 + or - 0.5) by 10 to the -11th power erg/sq cm per sec, which corresponds to a luminosity of 1.4 by 10 to the 45th power erg/s at 530 Mpc. Subsequent radio observations between 1.46 and 90 GHz were made at the NRAO Very Large Array and 36-foot (11-m) installations. The radio spectrum rises sharply toward higher frequencies and, below about 100 GHz, is indicative of a self-absorbed synchrotron spectrum from an extremely compact, rapidly evolving object.

Schnopper, H. W.↗

NASA NTRS2019

All-Sky Medium-Energy Gamma-Ray Observatory (AMEGO)

The gamma-ray energy range from a few hundred keV (kiloelectronvolts) to a few hundred MeV (megaelectronvolts) has remained largely unexplored since the pioneering but limited observations by COMPTEL (The Imaging Compton Telescope) on the CGRO (Compton Gamma Ray Observatory) (1991-2000). Fundamental astrophysics questions can be addressed by a mission in the MeV range, from astrophysical jets and extreme physics of compact objects to a large population of unidentified objects. Such a mission will also provide critical inputs for multimessenger astrophysics by identifying and exploring the astrophysical objects that produce gravitational waves and neutrinos. To address these questions, we are developing AMEGO: All-sky Medium Energy Gamma-ray Observatory, as a NASA probe-class mission, to investigate the energy range from 200 keV to greater than10 GeV with good energy (ranging from less than 1 percent at the low end to approximately 10 percent at the high end) and angular resolution (from 2 to 6 degrees depending on energy) and with sensitivity a factor of 20-50 better than previous instruments. Measurements at these energies are challenging, mainly due to the fact that two photon interaction processes, Compton scattering and pair production, compete. These interaction processes require different approaches in both detection and data analysis, and consequently in the instrument concept. AMEGO will be capable of measuring both Compton-scattering events at lower energies and pair-production events at higher energies. AMEGO will also have sensitivity to linear polarization of detected radiation at a level of 20 percent minimum detectable polarization from a source 1 percent of the Crab intensity, observed for 106 seconds. AMEGO will be operating mainly in scanning (discovery) mode with a field-of-view of 2.5 sr (Special Relativity) (20 percent of the sky observation any time), with the capability to be pointed to particular regions of interest..

Moiseev, Alexander↗

NASA NTRS1987

IRAS and ground-based observations of star formation regions in the Magellanic clouds

The Infrared Astronomy Satellite (IRAS) detected several hundred individual regions of star formation in the Large and Small Magellanic Clouds. Nearly two dozen of the brightest such sources were searched for from the ground at 10 microns; most of these were located and measured at wavelengths from 0.6 to 20 microns. Three principle results emerge from this study: First, the IRAS data show that star formation is considerably less active in the SMC than in the LMC, relative either to mass, luminosity, or H I content. The reduced activity in the SMC is consistent with the smaller amount of molecular material inferred from CO observations. Second, the sizes of the objects range from less than a few arcsecs (objects which look like extremely compact HII regions, with little or no extended radio, optical, or infrared emission) to some tens of arcsecs across (giant HII regions, of which the largest and brightest is 30 Doradus). Third, there are no obvious differences in the characteristics of the central portions of the LMC and SMC sources; all look like Galactic H II regions of similar luminosity.

Elias, Jonathan H.↗

DOE OSTI2024

Multiple Peaks and a Long Precursor in the Type IIn Supernova 2021qqp: An Energetic Explosion in a Complex Circumstellar Environment

Abstract We present optical photometry and spectroscopy of the Type IIn supernova (SN) 2021qqp. Its unusual light curve is marked by a long precursor for ≈300 days, a rapid increase in brightness for ≈60 days, and then a sharp increase of ≈1.6 mag in only a few days to a first peak ofM r ≈ −19.5 mag. The light curve then declines rapidly until it rebrightens to a second distinct peak ofM r ≈ −17.3 mag centered at ≈335 days after the first peak. The spectra are dominated by Balmer lines with a complex morphology, including a narrow component with a width of ≈1300 km s −1 (first peak) and ≈2500 km s −1 (second peak) that we associate with the circumstellar medium (CSM) and a P Cygni component with an absorption velocity of ≈8500 km s −1 (first peak) and ≈5600 km s −1 (second peak) that we associate with the SN–CSM interaction shell. Using the luminosity and velocity evolution, we construct a flexible analytical model, finding two significant mass-loss episodes with peak mass loss rates of ≈10 and ≈5M ⊙ yr −1 about 0.8 and 2 yr before explosion, respectively, with a total CSM mass of ≈2–4M ⊙ . We show that the most recent mass-loss episode could explain the precursor for the year preceding the explosion. The SN ejecta mass is constrained to be ≈5–30M ⊙ for an explosion energy of ≈(3–10) × 10 51 erg. We discuss eruptive massive stars (luminous blue variable, pulsational pair instability) and an extreme stellar merger with a compact object as possible progenitor channels.

Astronomy & Astrophysics↗

NASA NTRS2010

New Evidence for a Black Hole in the Compact Binary Cygnus X-3

The bright and highly variable X-ray and radio source known as Cygnus X-3 was among the first X-ray sources discovered, yet it remains in many ways an enigma. Its known to consist of a massive. Wolf-Rayet primary in an extremely tight orbit with a compact object. Yet one of the most basic of pa.ranietern the mass of the compact object - is not known. Nor is it even clear whether its is a neutron star or a black hole. In this Paper we present our analysis of the broad-band high-energy continua covering a substantial range in luminosity and spectral morphology. We apply these results to a recently identified scaling relationship which has been demonstrated to provide reliable estimates of the compact object mass in a number of accretion powered binaries. This analysis leads us to conclude that the compact object in Cygnus X-3 has a mass greater than 4.2 solar mass thus clearly indicative of a black hole and as such resolving a longstanding issue. The full range of uncertainty in our analysis and from using a. range of recently published distance estimates constrains the compact object mass to lie between 4.2 solar mass and 14.4 solar mass. Our favored estimate, based on a 9.0 kpc distance estimate is approx. l0 solar mass, with the. error margin of 3.2 solar masses. This result may thus pose challenges to shared-envelope evolutionary models of compact binaries. as well as establishing Cygnus X-3 as the first confirmed accretion-powered galactic gamma: ray source.

Shrader, Chris R.↗

DOE OSTI2022

The role of supernova convection for the lower mass gap and the isolated binary formation of gravitational wave sources

Understanding astrophysical phenomena involving compact objects requires an insight about the engine behind core-collapse supernovae (SNe) and the fate of the stellar collapse of massive stars. In particular, this insight is crucial in developing an understanding of the origin and formation channels of the growing populations of detected black hole-black hole, black holeneutron star and neutron star-neutron star mergers. The timescale of convection growth may have a large effect on the strength of SN explosion and therefore also on the mass distribution of stellar remnants. We adopt new formulas for the relation between the pre-SN star properties and their remnants (Fryer et al. 2022) and check how they impact population of double compact object (DCO) mergers formed via isolated binary evolution. The new formulas give one ability to test wide spectrum of assumptions on the convection growth time. In particular, different variants allow for a smooth transition between having a deep mass gap and a remnant mass distribution filled by massive neutron stars and low mass black holes. We present distribution of masses, mass ratios and the local merger rate densities of DCO for different variants of new formulas and test them together with different approaches to other highly uncertain processes. We find that mass distribution of DCO mergers is sensitive to adopted assumption on SN convection growth timescale up to $m_1$ + $m_2$ ≲ 35$M_⊙$. Between two extreme tested variants the probability of compact object formation within the mass gap may differ up to ~ 2 orders of magnitude.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

The role of supernova convection for the lower mass gap in the isolated binary formation of gravitational wave sources

ABSTRACT Understanding the astrophysical phenomena involving compact objects requires an insight about the engine behind the core-collapse supernovae (SNe) and the fate of the stellar collapse of massive stars. In particular, this insight is crucial in developing an understanding of the origin and formation channels of the growing populations of the detected black hole–black hole, black hole–neutron star, and neutron star–neutron star mergers. The time-scale of convection growth may have a large effect on the strength of SN explosion and therefore also on the mass distribution of stellar remnants. We adopt new formulas for the relation between the pre-SN star properties and their remnants and check how they impact the population of double compact object (DCO) mergers formed via the isolated binary evolution. The new formulas give one the ability to test a wide spectrum of assumptions on the convection growth time. In particular, the different variants allow for a smooth transition between having a deep mass gap and a remnant mass distribution filled by massive neutron stars and low-mass black holes. We present the distribution of masses, mass ratios, and the local merger rate densities of DCO for the different variants of new formulas and test them together with different approaches to other highly uncertain processes. We find that the mass distribution of DCO mergers is sensitive to the adopted assumption on the SN convection growth time-scale up to $m_1+m_2 \lesssim 35 \, \mathrm{M}_{\odot }$. Between the two extreme tested variants the probability of compact object formation within the mass gap may differ by up to approximately two orders of magnitude.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2018

MoonBEAM: Gamma-Ray Burst Detectors on SmallSAT

Moon Burst Energetics All-sky Monitor (MoonBEAM) is a CubeSat concept of deploying gamma-ray detectors in cislunar space to improve localization precision for gamma-ray bursts by utilizing the light travel time difference between a spacecraft in Earth and cislunar orbit. MoonBEAM is designed with high TRL components to be flight ready. This instrument would probe the extreme processes in cosmic collision of compact objects and facilitate multi-messenger time-domain astronomy to explore the end of stellar life cycles and black hole formations.

gamma-ray burst cubesat↗

NASA NTRS2018

MoonBEAM: A Beyond Earth-Orbit Gamma-Ray Burst Detector for Gravitational-Wave Astronomy

Moon Burst Energetics All-sky Monitor (MoonBEAM) is a CubeSat concept of deploying gamma-ray detectors in cislunar space to improve localization precision for gamma-ray bursts by utilizing the light travel time difference between different orbits. We present here a gamma-ray SmallSat concept in Earth-Moon L3 halo orbit that is capable of rapid response and provide a timing baseline for localization improvement when partnered with an Earth-orbit instrument. Such an instrument would probe the extreme processes in cosmic collision of compact objects and facilitate multi-messenger time-domain astronomy to explore the end of stellar life cycles and black hole formations.

gamma-ray burst cubesat↗

NASA NTRS2018

MoonBEAM: A Beyond Earth-Orbit Gamma-Ray Burst Detector for Multi-Messenger Astronomy

Moon Burst Energetics All-sky Monitor (MoonBEAM) is a CubeSat concept of deploying gamma-ray detectors in cislunar space to increase gamma-ray burst detections and improve localization precision with the timing triangulation technique. A gamma-ray instrument in cislunar orbit will have greatly reduced sky blockage compared to instruments in low Earth orbit. Working in conjunction with another instrument in low Earth orbit, MoonBEAM can also help constrain the arrival direction of the wavefront to an annulus on the sky by utilizing the light arrival times between the different orbits. This method has been demonstrated by the Interplanetary Gamma- Ray Burst Timing Network. However, delays in data downlink for instruments outside the Tracking and Data Relay Satellite network prevent rapid follow-up observations. We present here a gamma-ray CubeSat concept in Earth-Moon L3 halo orbit that is capable of faster response and provide a timing baseline for localization improvement. Such an instrument would aid in the gravitational wave follow-up observations in other wavelengths to identify the gamma-ray burst afterglow and kilonova emission. Reducing the region of interest makes identifying afterglows much faster, allowing for rapid on-source observations and monitoring of the rise and decay times. It will also prevent source confusion between two transients and enable robust association. A gamma-ray detection could also increase the confidence of a simultaneous but marginal gravitational wave signal, extending the detection horizon. MoonBEAM is a 12U CubeSat concept of deploying gamma-ray detectors in cislunar space to increase gamma-ray burst detections and improve localization precision with the timing triangulation technique. Such an instrument would probe the extreme processes in cosmic collision of compact objects and facilitate multi-messenger time-domain astronomy to explore the end of stellar life cycles and black hole formations.

gamma-ray Cubesat↗

NASA NTRS2018

MoonBEAM: A Beyond Earth-Orbit Gamma-Ray Burst Detector for Multi-Messenger Astronomy

MoonBEAM is a 12U CubeSat concept of deploying gamma-ray detectors in cislunar space to increase gamma-ray burst detections and improve localization precision with the timing triangulation technique. Such an instrument would probe the extreme processes in cosmic collision of compact objects and facilitate multi-messenger time-domain astronomy to explore the end of explore the end of stellar life cycles and black hole formation.

Beyond Earth-Orbit↗

NASA NTRS2019

X-Ray Follow-Up of Extragalactic Transients

Most violent and energetic processes in our universe, including mergers of compact objects,explosions of massive stars and extreme accretion events, produce copious amounts of X-rays. X-ray follow-up is an efficient tool for identifying transients: (1) X-rays can quickly localize transients with large error circles; (2) X-rays reveal the nature of transients that may not have unique signatures at other wavelengths. Here, we identify key science questions about several extragalactic multi-messenger andmulti-wavelength transients, and demonstrate how X-ray follow-up helps answer these questions.

Kara, Erin↗