For most people, when we look at the stars in the sky, surely we find that all stars are almost identical to each other, the sparkling glow of gas. The question is, how do we know how old the star is?
Not long ago, astronomers have found a method to determine the age of stars accurately from observing how the star is rotating.Like a top that is rotated on the table, how soon or slowly the star rotates can be a determinant of what the age of a star is. It was delivered by astronomer Soren Meibom of Harvard-Smithsonian Center for Astrophysics at the 218th meeting of the American Astronomical Society.
Why do astronomers need to understand the age of a star? Star age studies have a very important role in various studies in astronomy, specifically of course for the search for planets outside the Solar System, studying how its formation, its development, and why every planetary system that has been discovered is so unique to one another. By knowing the star age, then we can determine the age of the planets, as well as whether there might be a life that had grown out there. The older the age of the planet, the more likely it is that life is formed, because as it is known the planetary system that resides on a star usually forms along with the birth of the star itself.
Knowing the age of a star tends to be easy to determine if the star to be measured is within a cluster system. It is a basic knowledge for astronomy to obtain the color and brightness of the stars in the clusters to determine the age of the clusters, but the condition will be very difficult if the age-determined star is not in a cluster system. As the stars that have been discovered have planetary systems, most are not in clusters, thus determining their age to be a challenge in astronomical studies.
Research conducted by Meibon et al using observations of the Kepler rides, by measuring the rotation ratio of a 1 billion-year-old group referred to as NGC 6811. This value is almost twice that of the previous study, and the age around it is still said to be investigated in clusters young.
This study provides a new understanding of the relationship of star rotation ratio to its age. If the validity of the star and age rotation relationship can be obtained, then the measurement of the star rotation period of each star can be used to determine its age - a technique known as gyrochronology - but this can not necessarily be used.
As the Earth time system requires standards, the timing system must be calibrated to a standard. As we on Earth declare that a year consists of 365 days, etc., so in order to obtain the conformity of time, it must be possible to obtain a standard.
For that, the first step that the researchers are doing is to start by measuring a cluster system that has been known to his age. By measuring the rotation of the stars of the cluster members, it can be studied the ratio of the rotation of the stars to determine its age. Measurement of star rotation of cluster members at different ages can connect between the rotation and its age.
To be able to measure the spin of a star, astronomers must get a star's brightness changes due to the star's spots on the star's surface, just as the sunspots on the Sun's surface. If there are spots formed on the surface and are in the direction to the observer, then the star will experience a little dimming, until when the spots disappear, and the star back slightly more luminous. By determining how long the spots rotate on the star's aperture, it can be determined how quickly the star is observed spinning.
Of course, the change in the brightness of the star due to spots is very, very small, smaller than one percent and become smaller in older stars. Thus the measurement of star rotation in stars older than half a billion years cannot be made from the Earth's surface due to Earth's atmospheric disturbances. But the problem has now been solved by observing the Kepler spacecraft because it has been designed to measure the star's brightness with great precision in order to determine the planetary system of stars.
Surely determining the rotation-age relationship in the case of NGC 6811 is not an easy job for Meibom et al because they have spent four years determining the star member of the cluster or the coincidence of other stars in the same direction. This is done using a device called Hectochelle mounted on the MMT telescope at Mt. Hopkins south Arizona. The Hectochelle tool can observe 240 stars simultaneously, and thus has observed about 7000 stars during its four years of observation. After knowing the stars that are members of the cluster, then the data from Kepler is used to determine how fast the stars are spinning.
They found a rotation period of between 1 and 11 days (which is hotter and massive rotates faster), compared with the Sun whose turn ratio is only 30 days. The most important of their findings is the relationship of star mass with the rotation ratio with small data distribution. These findings confirm that gyrochronology is a new method that can be used to study the age of a star.
Tim Meibom is currently planning to study an older cluster system to calibrate their star timers. This is certainly a more difficult step because older stars rotate more slowly and have fewer spots, which means the brightness changes will be very, very small.
Meibom et al's work has become a leap in the understanding of how the stars in the sky (including the Sun) work, as well as on the understanding of planetary systems in distant stars.
Reference :
- http://www.iflscience.com/space/scientists-age-stars-based-their-spin/
- http://www.iflscience.com/space/scientists-age-stars-based-their-spin/
- https://www.scientificamerican.com/article/how-do-scientists-determi/
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