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Astronomers have tracked AT 2025abao, a luminous red nova in the Andromeda galaxy, documenting the complete evolution of a common envelope event where a main-sequence star spiraled into the expanding envelope of a dying giant star. Through comprehensive modeling, researchers determined that a 1.4 solar mass companion star inspiraled through the wind of a 6.9 solar mass asymptotic giant branch star over eight years before plunging into its envelope, ejecting approximately 0.92 solar masses of material. Critically, the models indicate both stellar components survived without merging, remaining in an eccentric orbit at least 400 days after the event began.
Why it matters
This represents potentially the first direct observation of common envelope evolution producing a close binary system, a process that is theoretically crucial for forming compact binaries like those that produce gravitational waves but has never been fully observed before. Understanding this process helps explain how neutron star and black hole binaries form in nature.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Abstract: Luminous red novae (LRNe) are potential signatures of common envelope evolution (CEE), a critical yet poorly understood phase in compact binary formation. AT 2025abao, an LRN in the Andromeda galaxy, originated from an asymptotic giant branch (AGB) progenitor and exhibited a prolonged pre-outburst transient. Lacking direct constraints on the companion, however, the system’s evolutionary fate remains unclear. Here, we unravel the binary nature of AT 2025abao by modeling its complete evolution, from precursor to final outcome. We show that the eight-year infrared precursor arises from a $approx1.4^{+0.2}_{-0.3},M_{odot}$ main-sequence companion inspiralling through the wind of a $approx 6.9,M_{odot}$ AGB star. As CEE commences, the companion plunges into the envelope and launches a shock. Radiation hydrodynamic modeling of this outburst constrains the total ejecta mass to $approx 0.92,M_{odot}$ and energy to $approx 1.25times 10^{47},$erg, revealing that only $approx 0.57,M_{odot}$ becomes unbound. Subsequent radiative transfer simulations successfully reproduce the evolving spectral energy distribution. Crucially, our models indicate the main-sequence companion and AGB core survive in an eccentric orbit without merging at least 400 days after CEE onset. AT 2025abao may therefore be the first observed CEE event caught forming a close compact binary, bridging a long-standing observational gap in compact binary formation.
Source: Unravelling the Nature of AT 2025abao: From Precursor to Final Fate