Astronomers have solved the mystery of how some stars remain young, bright and blue despite being almost as old as the universe itself. In other words, stars cannibalize their sibling stars.
These timeless objects, known as blue stragglers, have puzzled astronomers for more than 70 years. “Blue stragglers are hydrogen-burning stars with unusually heavy cores that, according to single-star evolution theory, should not exist,” the researchers wrote in a paper published January 3 in the same journal. nature communications.
Searching for stars beyond their age
Scientists have previously argued that blue stragglers can form in two ways. One is due to violent collisions between two stars, and the other is due to more subtle interactions between stars. binary system Pairs of stars orbit each other and exchange gas.
The research team found that the latter scenario was more likely.
Galactic globular clusters are perfect places to study stellar interactions between gas-sucking binary star systems. These globular clusters contain thousands or millions of stars, held together by their collective gravity. With so many stars living in regions just tens or hundreds of light-years across, star clusters are some of the densest stellar environments in the universe. Therefore, they host many stellar collisions and many binary star systems.
cluster too incredibly old. “Their age is about 12 years old. [billion years]Therefore, it is comparable to the age of the universe. ” 13.8 billion years old, Francesco FerraroThe study’s lead author, a professor of astronomy at the University of Bologna in Italy, told Live Science via email. “In fact, they are the oldest population in our galaxy.” This means a single star within each cluster houses blue stragglers formed during the period of galaxy formation.
Old stars also emit radiation at different wavelengths. So the researchers used JWST’s ultraviolet filter to distinguish between the blue stragglers and their older cluster friends. Because they are hotter, young stars emit more radiation at shorter wavelengths than older red clusters, which emit less in this region. electromagnetic spectrum.
amazing and wonderful scenario
Perhaps counterintuitive, the researchers found that blue stray stars are rarer in dense stellar environments, even though these regions are more likely to foster interactions between stars. Rather, stragglers are significantly more common in calm, low-density regions where stars are far apart and “vulnerable binary star systems are more likely to survive.”
The researchers used established quantitative measures that relate the number of blue stragglers to characteristics of the host cluster, such as brightness. The measurements revealed that blue straggler populations vary widely, from 3 to 58 per luminosity unit, which is equivalent to the brightness of 10,000 suns. Brightness is therefore related to the overall mass of the cluster, and therefore its density.
Using the same measure, the researchers calculated that the number of regular stars in a cluster remains relatively constant. This suggests that stragglers and binary systems are particularly sensitive to environmental density.
“Crowded star clusters are not friendly places for stellar partnerships,” study co-authors enrico vesperinisaid astronomers at Indiana University in a paper. statement. “When the universe is small, binaries are more easily destroyed and the stars lose the chance to stay young.”
Therefore, crowded environments, such as locations close to the center of a cluster, may not be the good speed-dating venues they were supposed to be. The gravitational influence from large populations of stars creates a cosmic bumper car-like effect, disrupting binary star systems early in their evolution before they turn into blue stragglers. The researchers found that straggler formation and survival were 20 times more efficient in quieter, lower-density environments.
A new way to understand stellar evolution
In addition to solving astronomical mysteries, the study provides “a new way to understand how stars evolve over billions of years,” study co-authors said. barbara lanzoniastronomers from the University of Bologna said in a statement.
But billions of years from now, the blue stragglers may not be able to live a peaceful and quiet life. Because they are much more massive than their sibling stars, they are more likely to sink into the center of the cluster through a process called . dynamic friction. While this is unfortunate for calm stars, astronomers can use star clusters as “dynamic clocks” to estimate their age based on the distribution of blue stragglers.
Finally, these vibrant, fresh-faced stars highlight the dynamic star balance. If they had been born larger, they would have died long ago. supernova or white dwarf. Its modest size, less than 0.8 solar masses, allowed it to survive long enough to renew its lifespan, at the cost of consuming its brethren.