How old are the stars we see today
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Age of Stars We See Today
Understanding the age of stars is crucial for comprehending the broader dynamics of the universe. Recent advancements in astronomical techniques and theoretical models have provided more accurate estimates of stellar ages, particularly for the oldest stars.
Improved Age Estimates of Ancient Stars
Historically, there was a discrepancy where the oldest stars appeared to be older than the universe itself. This paradox has been resolved through improved theoretical models and precise data from the European Space Agency's Hipparcos star-mapping satellite. These advancements have revised the ages of ancient star systems, such as globular clusters, to approximately 12 billion years. Concurrently, observations from the Hubble Space Telescope and new methods for measuring cosmic distances have adjusted the estimated age of the universe to around 12 billion years as well.
Gyrochronology and Stellar Rotation
Gyrochronology, a technique that uses the rotation period of a star to determine its age, has been instrumental in age-dating stars. However, this method requires calibration with stars of known ages. Recent data from an intermediate-age open cluster (NGC 6819, 2.5 billion years old) and old field stars with ages determined through asteroseismology have shown that traditional period-age relations do not always hold. Specifically, older stars exhibit unexpectedly rapid rotation. This phenomenon has been attributed to weakened magnetic braking in stars that are more evolved than the Sun, suggesting a fundamental change in the nature of ageing stellar dynamos.
Methods for Determining Stellar Ages
Several methods have been developed over the past sixty years to determine the ages of old stellar systems and individual stars. These methods include the use of color magnitude diagrams (CMD) and asteroseismology. For instance, the ages of star clusters such as NGC 188 and M41 have been determined using CMD, with NGC 188 estimated to be around 4 billion years old and M41 approximately 220 million years old .
Conclusion
The stars we observe today, particularly the oldest ones, are estimated to be around 12 billion years old. This estimate aligns with the revised age of the universe, thanks to advancements in theoretical models and observational techniques. Methods like gyrochronology and CMD have been pivotal in refining our understanding of stellar ages, although challenges remain in accurately dating older stars due to phenomena like weakened magnetic braking.
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