A unicorn in monoceros: the 3 M⊙ dark companion to the bright, nearby red giant V723 Mon is a non-interacting, mass-gap black hole candidate
ABSTRACT We report the discovery of the closest known black hole candidate as a binary companion to V723 Mon. V723 Mon is a nearby ($d\sim 460\, \rm pc$), bright (V ≃ 8.3 mag), evolved (Teff, giant ≃ 4440 K, and Lgiant ≃ 173 L⊙) red giant in a high mass function, f(M) = 1.72 ± 0.01 M⊙, nearly circular binary (P = 59.9 d, e ≃ 0). V723 Mon is a known variable star, previously classified as an eclipsing binary, but its All-Sky Automated Survey, Kilodegree Extremely Little Telescope, and Transiting Exoplanet Survey Satellite light curves are those of a nearly edge-on ellipsoidal variable. Detailed models of the light curves constrained by the period, radial velocities, and stellar temperature give an inclination of $87.0^{\circ ^{+1.7^\circ }}_{-1.4^\circ }$, a mass ratio of q ≃ 0.33 ± 0.02, a companion mass of Mcomp = 3.04 ± 0.06 M⊙, a stellar radius of Rgiant = 24.9 ± 0.7 R⊙, and a giant mass of Mgiant = 1.00 ± 0.07 M⊙. We identify a likely non-stellar, diffuse veiling component with contributions in the B and V band of ${\sim }63{{\ \rm per\ cent}}$ and ${\sim }24{{\ \rm per\ cent}}$, respectively. The SED and the absence of continuum eclipses imply that the companion mass must be dominated by a compact object. We do observe eclipses of the Balmer more »
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Award ID(s):
Publication Date:
NSF-PAR ID:
10280008
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
504
Issue:
2
Page Range or eLocation-ID:
2577 to 2602
ISSN:
0035-8711
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2. ABSTRACT Using ASAS-SN data, we find that the bright ($V\sim 13.5$ mag) variable star MACHO 80.7443.1718 (ASASSN-V J052624.38–684705.6) is the most extreme heartbeat star yet discovered. This massive binary, consisting of at least one early B-type star, has an orbital period of $P_{\rm ASAS-SN}=32.83627\pm 0.00846\, {\rm d},$ and is located towards the LH58 OB complex in the LMC. Both the ASAS-SN and TESS light curves show extreme brightness variations of ${\sim }40{{\ \rm per\ cent}}$ at periastron and variations of $\sim 10{{\ \rm per\ cent}}$ due to tidally excited oscillations outside periastron. We fit an analytical model of the variability caused by the tidal distortions at pericentre to find orbital parameters of $\omega =-61.4^\circ$, $i=44.8^\circ$, and $e=0.566$. We also present a frequency analysis to identify the pulsation frequencies corresponding to the tidally excited oscillations.
3. ABSTRACT We examine massive black hole (MBH) mergers and their associated gravitational wave signals from the large-volume cosmological simulation Astrid . Astrid includes galaxy formation and black hole models recently updated with an MBH seed population between 3 × 104h−1M⊙ and 3 × 105h−1M⊙ and a sub-grid dynamical friction (DF) model to follow the MBH dynamics down to 1.5 ckpc h−1. We calculate the initial eccentricities of MBH orbits directly from the simulation at kpc-scales, and find orbital eccentricities above 0.7 for most MBH pairs before the numerical merger. After approximating unresolved evolution on scales below ${\sim 200\, \text{pc}}$, we find that the in-simulation DF on large scales accounts for more than half of the total orbital decay time ($\sim 500\, \text{Myr}$) due to DF. The binary hardening time is an order of magnitude longer than the DF time, especially for the seed-mass binaries (MBH < 2Mseed). As a result, only $\lesssim 20{{\rm per \,cent}}$ of seed MBH pairs merge at z > 3 after considering both unresolved DF evolution and binary hardening. These z > 3 seed-mass mergers are hosted in a biased population of galaxies with the highest stellar masses of $\gt 10^9\, {\rm M}_\odot$. With the higher initial eccentricity prediction from Astrid , we estimate anmore »
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