How astronomer calculate the age of a star
For most people, when we see the stars in the sky, of course, we get that all the stars is near identical to each other, ie incandescent ball of gas. The question is, how do we know how old the star?
Recently, astronomers have obtained a method to accurately determine the age of the star from observing how the star rotates. Played like a top on the table, then how fast or slow rotation of the star can be a determinant of time what is the age of a star.
These comments were made by astronomers named Soren Meibom of the Harvard-Smithsonian Center for Astrophysics at the American Astronomical Society meeting 218.
Why do astronomers need to understand the age of a star?
Assessment of age stars have a very important role in various studies in astronomy, in particular of course to search for planets outside the solar system, studying how the formation, development, and why every planetary systems that have been found so unique from one another.
By knowing the age of a star, then we can determine the age of planets, and whether there may be a life that had grown out there.
The older age of the planet, the greater the possibility of life forms, because as has been known planetary systems are at a star usually formed simultaneously with the birth star itself.
Knowing the age of stars tend to be easy to determine if stars will be measured it was in a star cluster system.
Basic knowledge of astronomy is to obtain the relationship of color and brightness of stars in the cluster in order to determine the age group, but his condition would become very difficult when the star to be determined age are not in a single cluster system.
As the stars that have been found to have planetary systems, most are not in the group, so determining the age of a challenge in the study of astronomy.
Research conducted by Meibon et al use the observations of the Kepler spacecraft, by measuring the ratio of rotation on a 1 billion year old cluster called NGC 6811.
This value nearly double that of previous studies, and age it still be said about the investigation on the young group.
This study provides new insights on the relationship with the star’s rotation ratio of age. If the validity of the star’s rotation and age relations can be obtained, then the measurement of star’s rotation period of each star can be used to determine their age – a technique known as gyrochronology, but this is not necessarily to be used.
As the system time on Earth that require a standard, then the system timing (age) should be able to be calibrated to a standard.
As we on Earth states that one year consists of 365 days, etc, then for the time to get fit, must be obtained a standard.
To that end, the first step that the researchers did was to start from measurements of a cluster system that has been known to age.
By measuring the rotation of the cluster member stars, can be studied stars spin ratio to determine the age-old. Measurement of rotation of the star members of clusters at different ages can link between rotation and age.
To be able to measure the rotation of stars, astronomers have to get the star brightness changes caused by star spots on the surface of the star, as sun spots on the surface of the Sun.
If there are spots formed on the surface and is in the direction to the observer, the star will experience a slight dimming, until the spots disappear, and come back a little more luminous star.
By determining how long it rotating spots on the surface of the star, it can be determined how fast rotating star observed.
Of course, brightness changes due to star spots are very, very small, less than one percent and become smaller in the older stars.
Thus the star’s rotation measurements in stars that are older than half a billion years can not be done from the Earth’s surface due to the interference of Earth’s atmosphere.
But the problems it currently has to be overcome to use Kepler spacecraft observations, because the spacecraft had been designed to measure star brightness with great precision in order to determine the existence of planetary systems at the stars.
Of course, determining the age-rotation relationship in the case of NGC 6811 is not an easy job for Meibom et al because they have spent four years determine the cluster member stars or other stars who happen to be in the same direction of view.
This is done use a device called Hectochelle mounted on the MMT telescope on Mt. Hopkins southern Arizona. Hectochelle tool can observe 240 stars at once, and thus about 7000 stars have been observed during the four years of observations.
After learning about the stars who are members of the group, then the next data from the Kepler used to determine how fast the stars rotate.
They found a rotation period between 1 to 11 days (a more hot and massive spin faster), compared with the Sun’s rotation ratio is only 30 days.
The most important of their findings is the relationship with the star mass ratio of rotation with small data distribution. These findings confirm that gyrochronology is a new method that can be used to study the age of a star.
Meibom team is currently planning to study the system of the older group in order to calibrate the time determining their star. It certainly is a step that is more difficult because the older star rotates slower and have fewer spots, which means the changes will be very small.
Work Meibom et al that has been a leap in the understanding of how the stars in the sky (including the Sun) to work, as well as on the understanding of planetary systems in the distant stars.