These are the binary star “HD 148937” about 3,800 light years away in the direction of the constellation “Polymera” in the southern sky, and the nebulae “NGC 6164” and “NGC 6165” that extend around it. The bright star in the center is HD 148937, the one on the top right (northwest side) is called NGC 6164, and the one on the bottom left (southeast side) is called NGC 6165.
[▲Stellabinaria”HD148937″enebulose”NGC6164″e”NGC6165″fotografatedal”VLTSurveyTelescope(VST)”dell’OsservatoriodelParanal(Crediti:teamESO/VPHAS+.Ringraziamenti:CASU)]
It is generally believed that multiple stars in a binary star form at the same time, so they must be the same age. However, a research team led by astronomer Abigail Frost of the European Southern Observatory (ESO) has found that of the two massive stars that make up HD 148937, the companion star is estimated to be at least 2.7 million years old. million years and in some cases around 3.9 million years (depending on how the age of the companion star is estimated).
Another difference is that while the host star has a magnetic field, which is unusual for a massive star, the companion star does not. According to ESO, magnetic fields are a common feature of light stars like the Sun, but massive stars cannot maintain magnetic fields like lighter stars can. However, some massive stars have magnetic fields, which is one of the long-standing mysteries of astronomy.
Furthermore, NGC 6164 and NGC 6165, which surround HD 148937, are several hundred times younger than this binary star, forming only about 7,500 years ago. Furthermore, the nebula is said to be rich in elements such as nitrogen, carbon and oxygen. It is not surprising that they are detected in objects associated with “stellar death”, such as planetary nebulae and supernova remnants, but these are normally found deep within the star in a star like HD 148937. Since it is supposed to be an element, it may have been released from some destructive event that occurred in the past.
[▲StoriadiHD148937comeimmaginatadalgruppodiricerca.Inaltoasinistra:undisegnoimmaginariodiquandoeraunastellatriplaconduestellevicineeunastelladistante.Inaltoadestra:un’immagineimmaginariadiduestellevicinechesifondonoebrillanointensamente.Inbassoasinistra:impressionediunartistadiquandolaluminositàsièattenuataelestellesonodinuovovisibili.Inbassoadestra:immaginerealediHD148937(Crediti:ESO/L.CalçadateamVPHAS+.Ringraziamenti:CASU)]
Therefore, Frost and his colleagues analyzed HD 148937 using nine years of observational data acquired by the ESO-operated VLT Interferometer (VLTI) at the Paranal Observatory in Chile. VLTI is an interferometer that connects all four telescopes with a The 8.2 m aperture that makes up the Very Large Telescope (VLT) of the Paranal Observatory. As a result of the analysis, the research team developed the following scenario.
HD 148937 originally formed as a triple star composed of three stars. It is believed that two of the three stars were close to each other and one orbited at a distance from each other. Eventually, the two stars that were close to each other merged into a single star with a magnetic field, and the material ejected from the surrounding area formed a nebula. This scenario could successfully explain mysteries such as the different ages of host and companion stars, the unusual magnetic fields of massive stars, and the elemental composition of the nebula.
According to ESO, it has been predicted that the magnetic field of a massive star could be generated by the merger of two stars, and this result is the first direct evidence of this possibility and is attracting attention. “The magnetic field of a massive star is expected to last for only a short period of time compared to the age of the star, so we probably observed this rare phenomenon soon after it occurred,” Frost commented. An article summarizing the research group’s findings was published in Science.
[▲StoriadiHD148937comeimmaginatadalgruppodiricerca(video)]
（Credit: ESO/L. Calçada, M. Kornmesser/VPHAS+ team. Credit: CASU）
Furthermore, ESO is progressing with the construction of the next generation large telescope, the European Extremely Large Telescope (ELT), at Cerro Almazones, Chile. It is hoped that the ELT will allow us to look in more detail at what is happened with HD 148937, which could reveal even more surprises.
Source
- ESO – Beautiful nebula, violent story: the clash of stars solves the stellar mystery
- Gelo et al. – A massive magnetic star underwent a stellar merger (Science, arXiv)
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