V838 Monocerotis Shows First Evidence of Pulsations in Stellar Merger Remnant
Astronomers have detected the first observational evidence of pulsations in V838 Monocerotis, the remnant of a stellar merger that occurred in 2002, following its deepest dimming event since 2006. The dimming was caused by a transiting clump of freshly formed circumstellar dust, while spectroscopic signatures during recovery revealed a sub-photospheric pulsation shock similar to those seen in red supergiants and Mira variable stars. The findings confirm theoretical predictions of pulsational instability in post-merger stellar objects and suggest another dimming event may begin in northern summer 2026.
V838 Monocerotis, the remnant of a stellar coalescence event in 2002, entered its deepest dimming phase since 2006 in late 2025, prompting a detailed observational campaign using multiband photometry and high-resolution spectroscopy. Analysis of the photometric color evolution during the dimming is consistent with dust extinction characterized by AV=1.26 mag and RV=1.8, pointing to a transiting clump of small silicate or alumina grains of circumstellar origin. The photospheric effective temperature varied by no more than approximately 200 K throughout the event, ruling out intrinsic temperature changes as the primary cause of the dimming. During the recovery phase, hydrogen recombination lines from the Balmer, Paschen, and Brackett series appeared in emission with anomalous ratios matching those of pulsating Mira stars near maximum light, interpreted as a sub-photospheric pulsation shock. Low-ionization metal lines were simultaneously observed blueshifted by 90 km/s relative to the stellar rest frame, tracing shock-affected gas on the near side of the stellar disk. The spectroscopic sequence implies the 2026 dimming was itself triggered by a pulsation shock that occurred earlier in 2025, and the authors predict a further dimming event driven by the observed shock to begin in northern summer 2026. The study, submitted to Astronomy & Astrophysics, presents the first direct observational confirmation of pulsations in a stellar merger remnant.
What's missing
The study is a preprint submitted to Astronomy & Astrophysics and has not yet undergone peer review. The authors acknowledge the prediction of a further dimming event in summer 2026 but do not quantify the uncertainty range on this forecast. The physical mechanism linking the pulsation shock to dust clump formation in the circumstellar environment is described qualitatively but not fully modeled.
What different sources said
- arXiv astro-phCenter
Dimming and pulsation shock of the coalesced star V838 Monocerotis
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