10 pages, 3 figures, published in ApJ Letters
Observations have found black holes spanning ten orders of magnitude in mass across most of cosmic history. The Kerr black hole solution is however provisional as its behavior at infinity is incompatible with an expanding universe. Black hole models with realistic behavior at infinity predict that the gravitating mass of a black hole can increase with the expansion of the universe independently of accretion or mergers, in a manner that depends on the black hole's interior solution. We test this prediction by considering the growth of supermassive black holes in elliptical galaxies over $0<z\lesssim2.5$. We find evidence for cosmologically coupled mass growth among these black holes, with zero cosmological coupling excluded at 99.98% confidence. The redshift dependence of the mass growth implies that, at $z\lesssim7$, black holes contribute an effectively constant cosmological energy density to Friedmann's equations. The continuity equation then requires that black holes contribute cosmologically as vacuum energy. We further show that black hole production from the cosmic star formation history gives the value of $\Omega_{\Lambda}$ measured by Planck while being consistent with constraints from massive compact halo objects. We thus propose that stellar remnant black holes are the astrophysical origin of dark energy, explaining the onset of accelerating expansion at $z \sim 0.7$.
22 pages, 15 figures. Submitted to MNRAS
We report spectroscopic and photometric follow-up of a dormant black hole (BH) candidate from Gaia DR3. We show that the system, which we call Gaia BH2, contains a $\sim 1M_{\odot}$ red giant and a dark companion with mass $M_2 = 8.9\pm 0.3\,M_{\odot}$ that is very likely a BH. The orbital period, $P_{\rm orb} = 1277$ days, is much longer than that of any previously studied BH binary. Our radial velocity (RV) follow-up over a 6-month period spans most of the orbit's dynamic range in RV and is in excellent agreement with predictions of the Gaia solution. UV imaging and high-resolution optical spectra rule out all plausible luminous companions that could explain the orbit. The star is a bright ($G=12.3$), slightly metal-poor ($\rm [Fe/H]=-0.22$) low-luminosity giant ($T_{\rm eff}=4600\,\rm K$; $R = 7.9\,R_{\odot}$; $\log\left[g/\left({\rm cm\,s^{-2}}\right)\right] = 2.6$). The binary's orbit is moderately eccentric ($e=0.52$). The giant is strongly enhanced in $\alpha-$elements, with $\rm [\alpha/Fe] = +0.26$, but the system's Galactocentric orbit is typical of the thin disk. We obtained X-ray and radio nondetections of the source near periastron, which support BH accretion models in which the net accretion rate at the horizon is much lower than the Bondi-Hoyle-Lyttleton rate. At a distance of 1.16 kpc, Gaia BH2 is the second-nearest known BH, after Gaia BH1. Its orbit -- like that of Gaia BH1 -- seems too wide to have formed through common envelope evolution. Gaia BH1 and BH2 have orbital periods at opposite edges of the Gaia DR3 sensitivity curve, perhaps hinting at a bimodal intrinsic period distribution for wide BH binaries. Dormant BH binaries like Gaia BH1 and Gaia BH2 likely significantly outnumber their close, X-ray bright cousins, but their formation pathways remain uncertain.
12 pages, 8 figures, 2 tables, submitted to MNRAS
Many double white dwarf (WD) mergers likely do not lead to a prompt thermonuclear explosion. We investigate the prospects for observationally detecting the surviving remnants of such mergers, focusing on the case of mergers of Carbon-Oxygen WDs. For $\sim 10^4$ yr, the merger remnant is observationally similar to an extreme AGB star evolving to become a massive WD. Identifying merger remnants is thus easiest in galaxies with high stellar masses (high WD merger rate) and low star formation rates (low birth rate of $\sim 6-10 \,{\rm M_{\odot}}$ stars). Photometrically identifying merger remnants is challenging even in these cases because the merger remnants appear similar to He stars and post-outburst classical novae. We propose that the most promising technique for discovering WD merger remnants is through their unusual surrounding photoionized nebulae. We use CLOUDY photoionization calculations to investigate their unique spectral features. Merger remnants should produce weak hydrogen lines and strong carbon and oxygen recombination and fine-structure lines in the UV, optical and IR. With integral field spectrographs, we predict that hundreds of candidates are detectable in M87 and other nearby massive galaxies. Dust somewhat reduces the optical line emission for nebula radii $\lesssim 10^{17}$ cm, but the sources spend most of their time with larger radii when dust is less important. Our models roughly reproduce the WISE nebula surrounding the Galactic WD merger candidate IRAS 00500+6713; we predict detectable [Ne VI] and [Mg VII] lines with JWST but that the mid-IR WISE emission is dominated by dust not fine-structure lines.
14 pages, 9 figures, 3 tables, submitted to MNRAS, comments welcome
The multiwavelength observations of GRB afterglows, together with some high-performance particle-in-cell simulations, hint that the magnetic field may decay behind the shock front. In this work, we develop a numerical code to calculate the evolution of the accelerated electron distribution, their synchrotron and inverse-Compton (IC) spectra and accordingly the light curves (LCs) under the assumption of decaying microturbulence (DM) downstream of the shock, $\epsilon_B(t_p')\propto t_p'^{\alpha_t}$ with $t_p'$ the fluid proper time since injection. We find: (1) The synchrotron spectrum in the DM model is similar to that in the homogeneous turbulence (HT) model with very low magnetic field strength. However, the difference in the IC spectral component is relatively more obvious between them, due to the significant change of the postshock electron energy distribution with DM. (2) If the magnetic field decay faster, there are less electrons cool fast, and the IC spectral component becomes weaker. (3) The LCs in the DM model decay steeper than in the HT model, and the spectral evolution and the LCs in the DM model is similar to the HT model where the magnetic field energy fraction decreases with observer time, $\epsilon_B(t) \propto t^{5\alpha_t /8}$. (4) The DM model can naturally produce a significant IC spectral component in TeV energy range, but due to the Klein-Nishina suppression the IC power cannot be far larger than the synchrotron power. We apply the DM model to describe the afterglow data of GRB 190114C and find the magnetic field decay exponent $\alpha_t\sim -0.4$ and the electron spectral index $p\sim2.4$. Future TeV observations of the IC emission from GRB afterglows will further help to probe the poorly known microphysics of relativistic shocks.
arXiv only posting, contact Greg Henry for access to the data
4 pages, 4 figures, Astronomical Data Analysis Software and System XXXII (31 October-4 November 2022)
10 pages, 5 figures, 1 table (excluding Appendixes). Abstract abridged to meet arXiv requirements. Submitted to A&A
14 pages, 10 figures + appendices, submitted to MNRAS
Accepted for publication in ApJL. 15 pages, 8 figures
Accepted for publication in Frontiers of Astronomy and Space Sciences, 27 pages, 8 figures
9 pages, 4 figures, submitted to Astronomy & Astrophysics
Submitted to Astronomy and Astrophysics in the form of letter to the Editor, 5 pages, 1 figure, 1 table
10 pages, 4 figures, 2 tables (including appendix). Submitted to ApJL
11 pages, many figures. In press at MNRAS
13+10 pages, 9 figures
6 pages, 3 figures, 1 table, Accepted for publication in MNRAS-L
Submitted version. 53 pages, 9 figures, 6 tables
Accepted for publication in A&A
Updated version of Chapter 3 in "Active Galactic Nuclei"; F. Combes ed.; iSTE/Wiley 2022; DOI:10.1002/9781394163724. One figure (Fig. 2.) and several references added. A graduate-student level lecture on accretion discs in active galactic nuclei, not a review article. arXiv admin note: substantial text overlap with arXiv:1505.02172
22 pages, 11 figures, 3 tables
8 pages, 5 figures, 2 tables, accepted for publication in the proceedings of the 27th European Cosmic Ray Symposium
14 pages, 7 figures, 1 table
Submitted to Monthly Notices of the Royal Astronomical Society. Comments and discussions are welcome. Data and codes can be found at this https URL
5 pages, 8 figures, Conference paper
17 figures, 12 figures, 7 tables, accepted by MNRAS
16 pages, 14 figures, accepted for publication by MNRAS
10 pages, 4 figures, CSQCD IX proceedings
9 pages, 1 figure, 3 tables
Accepted by MNRAS
Published in Science Advances. Supplementary Materials available at this https URL
14 pages, Submitted to MNRAS
19 pages, 7 figures and 3 tables
10 pages, 7 figures
Submitted to MNRAS Main Joural
Accepted for publication in A&A
33 pages, 5 + 4 figures, 4 tables. To be submitted to JCAP. Comments welcome. arXiv admin note: text overlap with arXiv:2204.02945
Accepted for publication on MNRAS, 17 pages, 7 figures
12 pages, 6 figures, accepted for publication in A&A
19 pages, 16 figures - Will be submitted to MNRAS
19 pages, 16 figures, accepted for publication in MNRAS
20 pages, 15 figures. Accepted for publication in MNRAS
29 pages, 15 figures, submitted to PASJ
45 pages, 7 figures, 4 tables; accepted as a chapter in the book "Planetary systems now", eds. Luisa M. Lara and David Jewitt, World Scientific Publishing Co Pte Ltd
4 pages, 1 figure, Astronomical Data Analysis Software and System XXXII (2022)
31 pages, 20 figures, 1 table
21 pages, 17 figures, accepted by ApJ
13 pages, 4 figures
arXiv admin note: text overlap with arXiv:2111.07385
15 pages, 13 figures, Submitted to MNRAS
13 pages, 5 figures
17 pages, 12 figures, 2 tables, accepted in PASP
Accepted for publication in ApJL. 13 pages, 6 figures, 2 tables. The code is made publicly available online as a part of Prospector; the version used in this work corresponds to the state of the Git repository at commit 820ad72
Published in Planetary Science Journal
20+2 pages, 21+3 figures. Comments welcome. Code available at this https URL
16 pages, 10 figures
32 pages, 5 figures
14 pages, 6 figures. Comments welcome
7 pages, 4 figures (main texts) + 15 pages, 3 figures, 21 tables (supplement) - Submitted to Physical Review Letters
8 pages, 5 figures
12 pages, 4 figures
20 pages, 2 figures, accepted for publication in PRD
10 pages, 8 figures
13 pages, 9 figures, 1 table. First application of physics informed neural operators to solve magnetohydrodynamics equations
3 Figures
7 pages, 8 figures
Contribution to the "Journees de Rencontre des Jeunes Chercheurs (JRJC) 2021" proceedings