A seven-Earth-radius helium-burning star inside a 20.5-min detached binary

Abstract

Binary evolution theory predicts that the second common envelope (CE) ejection can produce low-mass (0.32-0.36 Msun) subdwarf B (sdB) stars inside ultrashort-orbital-period binary systems, as their helium cores are ignited under nondegenerate conditions. With the orbital decay driven by gravitational-wave (GW) radiation, the minimum orbital periods of detached sdB binaries could be as short as ~20 minutes. However, only four sdB binaries with orbital periods below an hour have been reported so far, while none of them has an orbital period approaching the above theoretical limit. Here we report the discovery of a 20.5-minute-orbital-period ellipsoidal binary, TMTS J052610.43+593445.1, in which the visible star is being tidally deformed by an invisible carbon-oxygen white dwarf (WD) companion. The visible component is inferred to be an sdB star with a mass of ~0.33 Msun, approaching that of helium-ignition limit, although a He-core WD cannot be completely ruled out. In particular, the radius of this low-mass sdB star is only 0.066 Rsun, about seven Earth radii, possibly representing the most compact nondegenerate star ever known. Such a system provides a key clue to map the binary evolution scheme from the second CE ejection to the formation of AM CVn stars having a helium-star donor, and it will also serve as a crucial verification binary of space-borne GW detectors in the future.

arXiv comment24 pages, 11 figures, 1 table, published on Nature Astronomy, URL: https://www.nature.com/articles/s41550-023-02188-2

References in corpus (88)

• Gaia Data Release 2. Summary of the contents and survey properties
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Gaia mission
• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• LSST: from Science Drivers to Reference Design and Anticipated Data Products
• Correcting for the Effects of Interstellar Extinction
• Modules for Experiments in Stellar Astrophysics (MESA): Binaries, Pulsations, and Explosions
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• The Galaxy Evolution Explorer: A Space Ultraviolet Survey Mission
• Modules for Experiments in Stellar Astrophysics (MESA): Convective Boundaries, Element Diffusion, and Massive Star Explosions
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• TianQin: a space-borne gravitational wave detector
• The Swift Ultra-Violet/Optical Telescope
• MESA Isochrones and Stellar Tracks (MIST) 0: Methods for the construction of stellar isochrones
• Local Kinematics and the Local Standard of Rest
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• A 3D Dust Map Based on Gaia, Pan-STARRS 1 and 2MASS
• Understanding the Lomb-Scargle Periodogram
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 microns Using GLIMPSE Data
• The Origin of Subdwarf B Star (I): the Formation Channels
• The origin of sdB stars (II)
• The construction and use of LISA sensitivity curves
• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• Probabilistic Forecasting of the Masses and Radii of Other Worlds
• VOSA: Virtual Observatory SED Analyzer. An application to the Collinder 69 open cluster
• Ultraviolet Radiation from Evolved Stellar Populations -- I. Models
• A $Gaia$ Data Release 2 catalogue of white dwarfs and a comparison with SDSS
• A Spectroscopic Survey & Analysis of Bright, Hydrogen-Rich White Dwarfs
• Galactic Rotation and Solar Motion from Stellar Kinematics
• Population synthesis for double white dwarfs. II. Semi-detached systems: AM CVn stars
• New evolutionary sequences for extremely low mass white dwarfs: Homogeneous mass and age determinations, and asteroseismic prospects
• Fully-Automated Reduction of Longslit Spectroscopy with the Low Resolution Imaging Spectrometer at Keck Observatory
• Periodic Flux Variability of Stars due to the Reflex Doppler Effect Induced by Planetary Companions
• Helium star donor channel for the progenitors of type Ia supernovae
• LISA verification binaries with updated distances from Gaia Data Release 2
• Models of low-mass helium white dwarfs including gravitational settling, thermal and chemical diffusion, and rotational mixing
• A selection of hot subluminous stars in the GALEX survey II. Subdwarf atmospheric parameters
• Beaming Binaries - a New Observational Category of Photometric Binary Stars
• ELLC - a fast, flexible light curve model for detached eclipsing binary stars and transiting exoplanets
• Science with the TianQin Observatory: Preliminary results on Galactic double white dwarf binaries
• General relativistic orbital decay in a seven-minute-orbital-period eclipsing binary system
• The Solar Neighborhood XXXII. The Hydrogen Burning Limit
• Mass accumulation efficiency in helium shell flashes for various white dwarf masses
• 3D kinematics of white dwarfs from the SPY project II
• White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14
• Adiabatic Mass Loss in Binary Stars. II. From Zero-Age Main Sequence to the Base of the Giant Branch
• Spectral analysis of sdB stars from the Hamburg Quasar Survey
• The hot subdwarf B + white dwarf binary KPD 1930+2752 - a Supernova Type Ia progenitor candidate
• A progenitor binary and an ejected mass donor remnant of faint type Ia supernovae
• Testing the white dwarf mass-radius relationship with eclipsing binaries
• A systematic search of Zwicky Transient Facility data for ultracompact binary LISA-detectable gravitational-wave sources
• Sciences with the 2.5-meter Wide Field Survey Telescope (WFST)
• The ELM Survey. VIII. 98 Double White Dwarf Binaries
• Lijiang 2.4-meter Telescope and its Instruments
• Evolution of Low-Mass Helium Stars in Semidetached Binaries
• Abundance studies of sdB stars using UV echelle HST/STIS spectroscopy
• The ESO supernovae type Ia progenitor survey (SPY)
• Population of hot subdwarf stars studied with Gaia III. Catalogue of known hot subdwarf stars: Data Release 2
• The orbital periods of subdwarf B binaries produced by the first stable Roche overflow channel
• A Jovian analogue orbiting a white dwarf star
• The first ultracompact Roche lobe-filling hot subdwarf binary
• He-accreting carbon-oxygen white dwarfs and type Ia supernovae
• Gaia Data Release 2 Catalogue of Extremely-low Mass White Dwarf Candidates
• A hot subdwarf-white dwarf super-Chandrasekhar candidate supernova Ia progenitor
• An 8.8 minute orbital period eclipsing detached double white dwarf binary
• Hot subdwarfs in close binaries observed from space I: orbital, atmospheric, and absolute parameters and the nature of their companions
• Orbital Decay in a 20 Minute Orbital Period Detached Binary with a Hydrogen Poor Low Mass White Dwarf
• Gravity and limb-darkening coefficients for compact stars: DA, DB, and DBA eclipsing white dwarfs
• A new class of Roche lobe-filling hot subdwarf binaries
• Identifying LISA verification binaries among the Galactic population of double white dwarfs
• Subdwarf B stars from the common envelope ejection channel
• Hot subdwarf Atmospheric parameters, Kinematics, and Origins -- Based on 1587 hot subdwarf stars observed in Gaia DR2 and LAMOST DR7
• Hot subdwarf stars identified in Gaia DR2 with spectra of LAMOST DR6 and DR7 I. Single-lined spectra
• Mass retention efficiencies of He accretion onto carbon-oxygen white dwarfs and type Ia supernovae
• The Tsinghua University-Ma Huateng Telescopes for Survey: Overview and Performance of the System
• A Systematic Search for Short-period Close White Dwarf Binary Candidates Based on Gaia EDR3 Catalog and Zwicky Transient Facility Data
• Formation of hot subdwarf B stars with neutron star components
• A dynamically discovered and characterized non-accreting neutron star -- M dwarf binary candidate
• Extremely low-mass white dwarf stars observed in Gaia DR2 and LAMOST DR8
• Minute-cadence Observations of the LAMOST Fields with the TMTS: I. Methodology of Detecting Short-period Variables and Results from the first-year Survey
• The Nearest Neutron Star Candidate in a Binary Revealed by Optical Time-domain Surveys
• The relation between outburst rate and orbital period in low-mass X-ray binary transients
• Minute-Cadence Observations of the LAMOST Fields with the TMTS: II. Catalogues of Short-Period Variable Stars from the First Two-Year Surveys
• Minimum Orbital Periods of H-Rich Bodies
• The effect of aspherical stellar wind of giant stars on the symbiotic channel of type Ia supernovae
• Practical Guidance for Bayesian Inference in Astronomy

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• Gravitational Wave Astronomy With TianQin
• A Catalogue of Ultracompact Mass-Transferring White Dwarf Binaries
• J0526+5934: a peculiar ultra-short period double white dwarf
• A post-common-envelope binary with double-peaked Balmer emission lines from TMTS
• Comparing population synthesis models of compact double white dwarfs to electromagnetic observations
• The first low-mass eclipsing binary within the fully convective zone from TMTS