Le téléscope spatial Hubble n’a pas dit son dernier mot. Des astrophysiciens des universités de Londres (University College London) et de Postdam l’ont utilisé pour observer une paire d’étoiles nommée SSN 7 localisée dans une région dite NGC 346 riche en formation d’étoiles du Petit Nuage de Magellan, une galaxie située à 200.000 années lumière de nous.
Pour en savoir plus sur SSN 7, ils ont fait appel aux observations rassemblées depuis une décade et provenant de 6 observatoires différents. Ils ont découvert que ces deux étoiles, d’une masse de 32 et 55 fois celle du soleil orbitaient l’une autour de l’autre en 3 jours, au lieu des 20 jours précédemment estimés.
Les observations montrent également que la plus grande de ces étoiles absorbe de la matière provenant de l’autre au rythme de 13 fois le poids de la Terre par an. Les chercheurs estiment qu’en environ 800.000 ans, la situation changera. La plus petite des étoiles s’effondrera sur elle-même et deviendra un trou noir.
Après plusieurs millions d’années, l’étoile restante commencera à s’étendre.
Alors le trou noir aura sa revanche. Il l’absorbera progressivement. Celle-ci à son tour deviendra un trou noir et les deux trous noirs spiraleront l’un autour de l’autre sur le modèle de ce que l’on observe de plus en plus dans les Observatoires d’ondes gravitationnelles.
Référence
| A&A Volume 674, June 2023 | ||
| Article | A56 | |
|---|---|---|
| Number of page(s) | 19 | |
| Section | Stellar structure and evolution | |
| DOI | https://doi.org/10.1051/0004-6361/202346055 | |
| Published online | 31 May 2023 | |
A low-metallicity massive contact binary undergoing slow Case A mass transfer:
A detailed spectroscopic and orbital analysis of SSN 7 in NGC 346 in the SMC⋆
. J. Rickard1,2 and D. Pauli1Received: 1 February 2023 Accepted: 26 March 2023
Abstract
Context. Most massive stars are believed to be born in close binary systems where they can exchange mass, which impacts the evolution of both binary components. Their evolution is of great interest in the search for the progenitors of gravitational waves. However, there are unknowns in the physics of mass transfer as observational examples are rare, especially at low metallicity. Nearby low-metallicity environments are particularly interesting hunting grounds for interacting systems as they act as the closest proxy for the early universe where we can resolve individual stars.
Aims. Using multi-epoch spectroscopic data, we complete a consistent spectral and orbital analysis of the early-type massive binary SSN 7 hosting a ON3 If*+O5.5 V((f)) star. Using these detailed results, we constrain an evolutionary scenario that can help us to understand binary evolution in low metallicity.
Methods. We were able to derive reliable radial velocities of the two components from the multi-epoch data, which were used to constrain the orbital parameters. The spectroscopic data covers the UV, optical, and near-IR, allowing a consistent analysis with the stellar atmosphere code, PoWR. Given the stellar and orbital parameters, we interpreted the results using binary evolutionary models.
Results. The two stars in the system have comparable luminosities of log(L1/L⊙) = 5.75 and log(L2/L⊙) = 5.78 for the primary and secondary, respectively, but have different temperatures (T1 = 43.6 kK and T2 = 38.7 kK). The primary (32 M⊙) is less massive than the secondary (55 M⊙), suggesting mass exchange. The mass estimates are confirmed by the orbital analysis. The revisited orbital period is 3 d. Our evolutionary models also predict mass exchange. Currently, the system is a contact binary undergoing a slow Case A phase, making it the most massive Algol-like system yet discovered.
Conclusions. Following the initial mass function, massive stars are rare, and to find them in an Algol-like configuration is even more unlikely. To date, no comparable system to SSN 7 has been found, making it a unique object to study the efficiency of mass transfer in massive star binaries. This example increases our understanding of massive star binary evolution and the formation of gravitational wave progenitors.
Based on observations with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-2655. Also based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere.
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