Betelgeuse's Buddy: X-Ray Constraints on the Nature of $\alpha$ Ori B

Abstract

The $\sim$$2100$d Long Secondary Period of Betelgeuse's optical lightcurve and radial velocity motivated the prediction of a low-mass stellar companion, expected to be at maximal apparent separation from Betelgeuse around December 2024. We carried out Director's Discretionary Time observations with the Chandra X-ray Observatory to identify any X-ray emission from the companion and constrain its nature as either a compact object or young stellar object (YSO). Past X-ray observations occurred at the wrong phase of the companion's orbit for optimal detection prospects and/or lacked the deep exposure required to constrain the typical X-ray luminosities of YSOs. In our 41.85 ks exposure with Chandra, we do not detect an X-ray source at the position of Betelgeuse. For an estimated hydrogen column density $N_H$$=$$6\times 10^{22}$ cm${}^{-2}$, we place a limit on the X-ray luminosity of $L_X$$\lesssim$$2\times 10^{30}$ erg s${}^{-1}$ ($\lesssim$$4.7\times 10^{-4}{L}_{\odot }$) in $0.5$$-$$8$ keV for a 10 MK plasma temperature spectral model, or $L_X$$\lesssim$$5\times 10^{29}$ erg s${}^{-1}$ ($\lesssim$$1.2\times 10^{-4}{L}_{\odot }$) for an absorbed power law with photon index $\Gamma$$=$$2$. These limits robustly exclude an accreting compact object (white dwarf or neutron star) as the companion. Solar mass YSOs with an age similar to Betelgeuse ($\sim$10 Myr) display a range of X-ray luminosities ($10^{28-32}$ erg s${}^{-1}$), and we can place upper bounds within this range for most absorbing columns. Based on these considerations, we conclude that the companion to Betelgeuse is likely a low-mass YSO.

15 pages including references and appendices, 4 figures, 3 tables. Accepted by ApJ. See also companion publication, Goldberg et al. 2025

References in corpus (31)

• Binary interaction dominates the evolution of massive stars
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Formation of Double Neutron Star Systems
• Observations of Protoplanetary Disk Structures
• Red supergiants as potential Type IIn supernova progenitors: Spatially resolved 4.6 micron CO emission around VY CMa and Betelgeuse
• Variability in red supergiant stars: pulsations, long secondary periods and convection noise
• The evolution of stellar triples: The most common evolutionary pathways
• A dusty veil shading Betelgeuse during its Great Dimming
• The enigmatic nature of the circumstellar envelope and bow shock surrounding Betelgeuse as revealed by Herschel. I. Evidence of clumps, multiple arcs, and a linear bar-like structure
• Standing on the shoulders of giants: New mass and distance estimates for Betelgeuse through combined evolutionary, asteroseismic, and hydrodynamical simulations with MESA
• Stellar triples on the edge; Comprehensive overview of the evolution of destabilised triples leading to stellar and binary exotica
• Betelgeuse Just Isn't That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse
• The Photospheric Temperatures of Betelgeuse during the Great Dimming of 2019/2020: No New Dust Required
• Effect of binary evolution on the inferred initial and final core masses of hydrogen-rich, Type~II supernova progenitors
• An Updated 2017 Astrometric Solution for Betelgeuse
• Wind-accreting Symbiotic X-ray Binaries
• Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse
• The Great Dimming of Betelgeuse: a Surface Mass Ejection (SME) and its Consequences
• Episodic Gaseous Outflows and Mass Loss from Red Supergiants
• The inhomogeneous sub-millimeter atmosphere of Betelgeuse
• The M Supergiant High Mass X-Ray Binary 4U 1954+31
• Stellar models and isochrones from low-mass to massive stars including pre-main sequence phase with accretion
• Evolution of X-ray Activity in <25 Myr Old Pre-Main Sequence Stars
• Orbital evolution with white-dwarf kicks
• SRGA J181414.6-225604: A new Galactic symbiotic X-ray binary outburst triggered by an intense mass loss episode of a heavily obscured Mira variable
• Analysis of photometric and spectroscopic variability of red supergiant Betelgeuse
• SOFIA-EXES Observations of Betelgeuse during the Great Dimming of 2019/2020
• pathfinder: A Semantic Framework for Literature Review and Knowledge Discovery in Astronomy
• A Rapidly Varying Red Supergiant X-Ray Binary in the Galactic Center
• The dusty circumstellar environment of Betelgeuse during the Great Dimming as seen by VLTI/MATISSE
• A massive AGB donor in Scutum X-1: Identification of the first Mira variable in an X-ray binary