As stars age their surface rotation slows down due to a loss of mass and angular momentum, but contrary to current theory, the phenomenon does not continue throughout the lives of these aging stars, according to new research published Monday in the journal Nature.
The rotational slowdown observed in older stars, which is the result of a loss of mass and angular momentum, was long thought to have continued unabated throughout their later years. In the new study, however, an international group of astronomers found that there comes a time in the life of every star when its rotation stops slowing down.
Take the sun, for example. As the study authors explained in a statement, it is beginning to slow down as its magnetic field interacts with particles flowing away from its surface. Researchers use a technique known as gyrochronology to estimate its age, and the age of other, similar stars.
Previous studies involving gyrochronology had indicated that the rotational rates of aging stars continued to slow down as they grew older and older, but the authors of the new study found that they stop slowing once they reach a certain age. This discovery could alter our understanding of how low-mass stars like the sun influence planets and other nearby objects as they age.
Changes in the sun could lessen impact on technology
According to study co-author Dr. Guy Davies from the University of Birmingham’s School of Physics and Astronomy, the slowdown in stellar rotation stops once a star reaches middle age. The sun, which is 4.5 billion years old, is nearing this point in its lifespan, which means that it should stop slowing down within the next few hundred million years, he added.
Once this change takes place, it will likely affect the way that the sun interacts with the Earth, Dr. Davies and his colleagues explained. For one thing, changes in the magnetic field expected to occur will likely result in a the emission of fewer high-energy particles and a reduction in the frequency of solar storms, reducing space weather-related risks to technology. Furthermore, this terminated slow down could make human space travel safer, they noted.
“This research has major implications for how we see the Sun in the wider context of other Sun-like stars in our Galaxy, some of which will harbor planets like our own,” Professor Bill Chaplin, head of solar and stellar research at Birmingham, said in a statement.
“Our findings might suggest a fundamental change in the nature of ageing stellar dynamos, with the Sun being close to the critical transition to much weaker magnetized winds. This weakened braking limits the diagnostic power of gyrochronology for those stars that are more than halfway through their main-sequence lifetimes,” he and his colleagues added in their study.
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Feature Image: The sun is nearing the point in its lifespan when it should stop slowing down within the next few hundred million years. Credit: NASA.
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