When observing two stars in the heart of a nebula astronomers at the European Southern Observatory (ESO) were surprised by some rare features: one of the stars appeared to be much younger than the other and, also unlike his companion, had a strong magnetic field .
Normally, observed pairs of stars tend to be very similar to each other, as if they were twins. In case of HD system 148937 located approximately 3,800 light-years away from Earth, the two stars, both with much greater mass than our Sun, not only appear to be different ages, but also have different characteristics.
The existence of a nebula, a cloud of gas and dust, around the stars only increased scientists' hypotheses that there was a story behind this system that was worth investigating.
“Finding a nebula around two massive stars is quite rare and led us to think that something different must have happened in this system. When we analyzed the data, we saw that, in fact, this was the case”, explained Abigail Frost, astronomer at ESO in Chile and main author of the study published this Thursday (11) in the journal Science.
Frost said she was “blown away by how special the system seemed to be.”
The most massive star appears to be at least 1.5 million years younger than the other. “Which is illogical, since these stars should have formed at the same time,” explained the astronomer.
Furthermore, the nebula that surrounds the stars, known as NGC 6164/6165 or Dragon's Egg, is approximately 7,500 years old. It is hundreds of times younger than both stars and has a high amount of elements that are usually found inside a star, rather than around it.
A violent story that unraveled a mystery
After investigating these mysteries, ESO scientists came to the conclusion that these peculiarities were the result of a violent history : data suggests that Originally three stars formed the HD 148937 system, two of which merged after a shock.
“The two inner stars merged violently, creating a magnetic star and ejecting material, which gave rise to the nebula. The third, most distant star gained a new orbit with the newly merged magnetic star, creating the binary system we currently observe at the center of the nebula,” said study co-author Laurent Mahy, currently a senior researcher at the Royal Observatory of Belgium. .
The data obtained by ESO to demonstrate what would have happened in the formation of the system as we see it today also helped solve a mystery that has troubled astronomers for a long time: how some massive stars get their magnetic fields .
Magnetic fields are a common feature in small stars, like our Sun, but more massive stars are generally unable to maintain them. Even so, some massive stars are magnetic, and scientists could not explain the cause of these exceptions.
Astronomers already suspected that the merger of two stars could result in the magnetic field, but this is the first time that evidence has been presented to support this theory.
“Magnetism in massive stars is not expected to last very long compared to the lifetime of the star, so we think we observed this rare event shortly after the merger occurred,” Frost added.
Source: CNN Brasil
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