Beautiful nebula, violent history: Clash of stars solves stellar mystery

When astronomers checked out a stellar pair on the coronary heart of a surprising cloud of gasoline and dust, they have been in for a shock. Star pairs are sometimes very related, like twins, however in HD 148937, one star seems youthful and, not like the opposite, is magnetic.

New knowledge from the European Southern Observatory (ESO) counsel there have been initially three stars within the system, till two of them clashed and merged. This violent occasion created the encompassing cloud and without end altered the system’s destiny.

“When doing background studying, I used to be struck by how particular this technique appeared,” says Abigail Frost, an astronomer at ESO in Chile and lead creator of the study, “A magnetic large star has skilled a stellar merger,” revealed in Science.

The system, HD 148937, is situated about 3800 light-years away from Earth within the path of the Norma constellation. It’s made up of two stars way more large than the sun and surrounded by a lovely nebula, a cloud of gasoline and dust. “A nebula surrounding two massive stars is a rarity, and it actually made us really feel like one thing cool needed to have occurred on this system. When wanting on the knowledge, the coolness solely elevated.”

“After an in depth evaluation, we may decide that the extra large star seems a lot youthful than its companion, which does not make any sense since they need to have shaped on the similar time,” Frost says. The age distinction—one star seems to be at the very least 1.5 million years youthful than the opposite—suggests one thing should have rejuvenated the extra large star.

One other piece of the puzzle is the nebula surrounding the celebrities, often known as NGC 6164/6165. It’s 7,500 years previous, lots of of instances youthful than each stars. The nebula additionally exhibits very excessive quantities of nitrogen, carbon and oxygen. That is stunning as these components are usually anticipated deep inside a star, not exterior; it’s as if some violent occasion had set them free.

To unravel the thriller, the staff assembled 9 years’ price of knowledge from the PIONIER and GRAVITY devices, each on ESO’s Very Massive Telescope Interferometer (VLTI), situated in Chile’s Atacama Desert. In addition they used archival knowledge from the FEROS instrument at ESO’s La Silla Observatory.

“We expect this technique had at the very least three stars initially; two of them needed to be shut collectively at one level within the orbit whereas one other star was way more distant,” explains Hugues Sana, a professor at KU Leuven in Belgium and the principal investigator of the observations.

“The 2 inside stars merged in a violent method, making a magnetic star and throwing out some materials, which created the nebula. The extra distant star shaped a brand new orbit with the newly merged, now-magnetic star, creating the binary we see right this moment on the heart of the nebula.”

“The merger situation was already in my head again in 2017 once I studied nebula observations obtained with the European House Company’s Herschel House Telescope,” provides co-author Laurent Mahy, at the moment a senior researcher on the Royal Observatory of Belgium.

“Discovering an age discrepancy between the celebrities means that this situation is essentially the most believable one and it was solely potential to point out it with the brand new ESO knowledge.”

This situation additionally explains why one of many stars within the system is magnetic and the opposite isn’t—one other peculiar characteristic of HD 148937 noticed within the VLTI knowledge.

On the similar time, it helps remedy a long-standing thriller in astronomy: how large stars get their magnetic fields. Whereas magnetic fields are a typical characteristic of low-mass stars like our sun, extra large stars can’t maintain magnetic fields in the identical approach. But some large stars are certainly magnetic.

Astronomers had suspected for a while that large stars may purchase magnetic fields when two stars merge. However that is the primary time researchers discover such direct proof of this taking place. Within the case of HD 148937, the merger should have occurred lately.

“Magnetism in large stars is not anticipated to final very lengthy in comparison with the lifetime of the star, so it appears we have now noticed this uncommon occasion very quickly after it occurred,” Frost provides.

ESO’s Extraordinarily Massive Telescope (ELT), at the moment below building within the Chilean Atacama Desert, will allow researchers to work out what occurred within the system in additional element, and maybe reveal much more surprises.