The key seems to be in the merger of medium-mass stars, according to researchers.
The unexpected occurrence of huge stars distant from their genesis in the disk of our Milky Way Galaxy has been explained by astronomers from Georgia State University.
Stars with masses greater than the Sun have very hot cores, which fuel rapid nuclear energy creation. They are among our galaxy’s brightest objects. However, since they burn up their hydrogen fuel so fast, their lives are brief, possibly 10 million years compared to the Sun’s 10 billion.
Because of their limited lifespan, they have little opportunity to go far from home. The vast majority of large stars are located in the flat disk region of our galaxy, where gas clouds are thick enough to drive star formation and astronomers discover newborn massive star clusters.
So, how did a huge star end up so far out from the disk of the galaxy?
“Astronomers are discovering enormous stars far distant from their birthplace, so far away that the journey takes longer than the star’s lifespan,” Georgia State astronomer Douglas Gies stated. “How this may happen is a hot question among scientists right now.”
This is the difficulty posed by HD93521, a big star located 3,600 light years above the disk of the galaxy. The journey time to reach this place much surpasses the anticipated age of this big star, according to a recent research by Gies and other astronomers from Georgia State University.
The researchers utilized a new distance estimate from the European Space Agency’s Gaia probe, as well as a spectrum analysis, to figure out the star’s mass, age, and speed across space. They discovered that HD93521 has a mass around 17 times that of the Sun, implying that it is about 5 million years old. The star’s speed, on the other hand, suggests that its voyage from the disk took far longer, about 39 million years.
The Georgia State researchers propose that HD93521 departed the disk as two lower-mass, longer-lived stars, rather than the one massive star we observe today, to explain the unusual disparity in the star’s lifespan and trip time. The Astronomical Journal has published its results.
The fact that HD93521 is one of the galaxy’s fastest revolving stars provides a hint to the riddle. Stars may spin up as a result of stellar mergers, which occur when two closely circling stars develop and collide over time to create a single star.
“HD93521 was most likely born as a nearby pair of medium-mass stars that were doomed to collide and merge into the single, fast-spinning star we see today,” Gies added.
Such stars of intermediate mass survive long enough to match HD93521’s extended flight duration.
HD93521 isn’t the first time a huge star has been discovered so distant from its origin. Peter Wysocki, a PhD student at Georgia State University, is looking at a faraway huge binary pair that is likely typical of the period shortly before a merger. IT Librae is the name of this star, which has an alignment that causes mutual eclipses when the two stars pass in front of each other. Estimates of star masses are derived from an examination of fluctuations in light output and movements seen in the spectra.
From the bulk findings, Wysocki discovers a similar conundrum: the anticipated age is substantially shorter than IT Librae’s disk transit time. However, the analysis also indicates that the lower-mass star in the pair has already started to transfer most of its mass to the higher-mass star, indicating that the pair is on the verge of merging. This implies that the higher-mass star was formerly a lower-mass star and is thus older than it looks.
These far-off enormous stars, according to Gies, give compelling evidence that nearby pairs of stars may combine to become even bigger stars, as well as crucial information about how quickly revolving massive stars can produce black holes with high spins.
The National Science Foundation provided funding for this research.