A cosmic mystery has been revealed through violence. A double star called HD 148937 doesn’t look like what we thought because there were once three of them. A new study has found that two original triplet stars merged to form not only the beautiful Dragon Egg Nebula that hosts the stars, but also two incompatible stars linked together in a gravitational dance.

“I was amazed at how special this system looked during the background reading,” says astronomer Abigail Frost of KU Leuven in Belgium and the European Southern Observatory in Chile.

“A nebula surrounding two massive stars is very rare, and it really made us feel like something amazing was going to happen in this system. “When we look at the data, it seems that the composure has increased even more.”

Located approximately 3,800 light-years from Earth, the system consists of two massive stars in a 26-year orbit. And they are huge – one has a mass of 29.9, the other has 26.6 solar masses. The theory suggests that this is large enough to form a black hole every time a star dies.

The larger of the two stars is really interesting. Preliminary studies show that it has a magnetic field. This is truly surprising because stars with a mass of about seven times the Sun generally do not have such a thing; They do not appear to have the convective interiors necessary to maintain a magnetic field like smaller stars.

That’s what intrigued Frost and his team. They analyzed nine years of observations of the system collected by ESO’s Very Large Telescope, as well as archival data from the MPG/ESO 2.2-meter telescope. This allowed them to characterize stars and their orbits in detail. And when they started looking closely, the researchers noticed something strange. Two massive stars in a binary system like this should be about the same age and formed in the same stellar nursery at about the same time.

But when the researchers analyzed the chemical composition of the stars, whose profile helps determine their age, they found that the older of the two stars is about 2.7 million years old, while the younger is at least 4.1 million years old. This is not an insignificant age difference.

And there is a nebula whose age is estimated to be about 7,500 years. Its existence is strange enough in itself; such nebulae often emit dying stars, but both stars in the nebula’s core are in the prime of their lives.

It also contains plenty of nitrogen, carbon and oxygen. These elements are often trapped inside stars rather than floating outside them. One possible explanation for magnetically massive stars is the merger of two smaller stars. Such an event could also cause the interior materials of stars to be released into the surrounding space. Together, the clues indicate that such a merger actually occurred in HD 148937.

“We believe there were at least three stars in this system initially; The two should be close to each other at the same point in the orbit, while the other star should be much further away, says astronomer Hugues Sana from KU Leuven.

“The two inner stars violently merged, forming a magnetic star and expelling some of the material that formed the nebula. The more distant star formed a new orbit with the newly merged, now magnetic star, forming the binary system we see today. At the center of the nebula.”

This would make HD 148937 the first definitive evidence that stellar mergers do indeed produce the magnetic fields we sometimes see orbiting massive stars. The expected rate of these mergers is consistent with the percentage of massive stars we see having magnetic fields.

And since these magnetic fields are thought to be very transient in space, this is also consistent with a relatively recent time frame for the merger, consistent with the estimated age range of the Dragon Egg Nebula. The team’s research was published on: Science.