Researchers discover violent past and merging stars explain strange age difference.

A team of scientists has uncovered the reason behind a unique star system, HD 148937, where two stars have a remarkable age gap of over a million years. Normally, stars in a binary system are very similar in age, but in this case, one of the stars is about 1.4 million years older than the other.

The researchers believe the unusual age difference can be traced to a violent past involving a third star. According to the team, HD 148937 originally consisted of three stars. Two of these stars were in close orbit, and a third star was much more distant. At some point, the two closer stars collided and merged, creating a nebula — a cloud of gas and dust — around the newly formed star. This violent collision, which likely happened about 2.6 million years ago, resulted in the younger star becoming magnetic, unlike its older companion.

This merger not only explains the age discrepancy but also sheds light on the formation of magnetic fields in massive stars, which are typically difficult to maintain. While magnetic fields are common in lower-mass stars like the Sun, they are much rarer in more massive stars. The discovery that this phenomenon can occur as a result of a stellar merger provides new insights into the behavior of such stars.

The scientists, led by Hugues Sana of KU Leuven in Belgium, believe that the merger of the two inner stars created a magnetic star, and the more distant star then formed a new orbit with the magnetic star, resulting in the binary system we observe today.

Dr. Abigail Frost, an astronomer at the European Southern Observatory (ESO), noted that the rarity of a nebula surrounding two massive stars made them suspect that something unusual had happened in this system. The magnetic field in one of the stars is particularly intriguing because such fields typically don’t last long in massive stars. This suggests that the scientists have captured this rare event shortly after it occurred, providing direct evidence of the formation of magnetic fields in massive stars following a stellar merger.

This research, based on nine years of data from ESO’s Very Large Telescope Interferometer (VLTI) in Chile, provides valuable insights into stellar evolution, especially in systems with high-mass stars. The study helps explain not only the age gap between the stars in HD 148937 but also contributes to understanding the complex processes that shape the characteristics of massive stars.