How do Scientists Calculate the Age of Stars

How do Scientists Calculate the Age of Stars and Which Star is the Oldest?

Stars | Astronomers have demonstrated that they can accurately calculate the age of a star, following the speed of rotation of the star around its own axis, according to BBC material, and according to Agerpres.

Scientists knew that the speed of rotation of stars declined over time, but until recently they had too little data to accurately calculate their age starting at the speed of rotation. This time, American astronomers have been able to measure the rotation speed of stars known to be over 1 billion years old, and the results obtained are conclusive for establishing a ratio between this rotation speed and the starry age, with a margin error of only 10%.

The results of their study were presented in Seattle on the occasion of the American Astronomical Society meeting and were also published by Nature magazine. Determining the age of stars is of utmost importance for astronomy, just as setting fossil age is of crucial importance for the study of biology. This method applies to so-called “cold stars” – stars in the Sun category or smaller ones (these are the most widespread stars in our galaxy and have longer lives than larger stars).

“They have the role of lanterns, illuminating even the earliest corners of our galaxy,” said Soren Meibom of the Harvard-Smithsonian Center for Astrophysics, the coordinator of this study.

Also, these colder stars also host the vast majority of Earth exoplanets that we have discovered so far. Most of the properties of a “cold start” like the Sun – its size, mass, brightness, and temperature – remain almost constant throughout its entire life, which makes it very difficult to find the age of such a star. The solution to measure rotation speed was first proposed in the 1970s and was named “gyro-chronology” in 2003.

“A cold star rotates very fast when it’s young, but this rotation is getting slower as the star gets old,” according to Meibom.

However, this method is not without difficulty. Astronomers find it difficult to track the rotation of a star and therefore call landmarks at its surface, such as sunspots, spots that produce only up to 1% of the star’s lustre. “Old” stars also pose more problems because they are less active and form fewer and smaller sunspots. The team coordinated by Dr Meibom used the images obtained with the Kepler Telescope, which is in the circumferential orbit since 2009. They have been able to measure the rotation speeds of 30 stars from a cluster known to be age about 2.5 billion years ago, called NGC 6819. Prior to the Kepler telescope mission, the astronomers had only very cold star data from very young clusters – all younger than 600 million years old, all rotating pretty fast – about once a week.

NGC 6811 and Keppler 66

In 2011, the team coordinated by Dr Meibom used the images captured by the Kepler telescope to study another star cluster, NGC 6811, with an estimated 1 billion years of age. The cooler stars in this cluster complete a rotation once in about 10 days. Besides these data, the only star we know about age and rotation speed is the Sun – 4.6 billion years and a 26-day spin. The stars in the newly studied cluster complete a rotation once in about 18 days. “This cluster helps us determine how good gyro-chronology is as a way of finding a star’s age,” according to Ruth Angus, a researcher at Oxford University.

Which Star is the Oldest Star?

The oldest star discovered so far by mankind seems to be even older than the universe itself, but a new study helps clarify this paradox. Earlier research has estimated that the “star Matusalem” dates back 16 billion years ago. This dating is problematic as most scientists believe that the Big Bang, the event that led to the conception of the Universe, took place about 13.8 billion years ago. Recently, a team of astronomers calculated a new age for the star Matusalem, using information about the distance, glow, composition and structure of this star.

“Using all of these ingredients we are at the age of 14.5 billion years, with an uncertainty that makes the age of the star compatible with the age of the universe,” commented Howard Bond, a Pennsylvania State University specialist and principal author of the new research.

Bond’s uncertainty is over-plus 800 million years, which means that the star could be 13.7 billion years old – being a little younger than the universe. Bond and his team of scientists studied Matusalem star, known as HD 140283, using the Hubble Space Telescope. The star has been known for over 100 years because it crosses the sky at a very high speed. “Matusalem” travels with 1.3 million kilometres per hour and covers a distance equal to the width of the full moon every 1,500 years. Researchers say that by repeatedly studying this star could get a more accurate age, unambiguously stating that HD 140283 is no longer “old” than the universe.
The new study was published in the journal Astrophysical Journal Letters.

Stars, Science and The age of the Universe

Physics and astronomy of the twentieth century have made remarkable progress to the point where we can know with certainty the age of the universe. However, with some humility, which is, of course, the science, we recognize not only the existence of mysteries but also the fact that behind the physical universe there are causes that transcend it and which we can not investigate with our own methods of science.

Our understanding of the size and age of the universe has evolved rapidly in the last thousand years. In Ptolemy’s cosmology, the earth is in the geometric centre of the universe, the sun and the stars rotating around it. Copernicus has overcome this conception, noting that the earth is actually rotating around the sun. The very idea of the centre of the universe disappeared later when it came to the conclusion that the sun is itself a star, one of the millions or, as it was later found, of the billions of stars in our galaxy, the Milky Way.

Even more recently, in the 20th century, it was discovered that our galaxy, which has approximately 200 billion stars, is one of approximately 200 billion galaxies in the visible universe. In 1929, American astronomer Edwin Hubble made an epochal discovery, ultimately resulting in calculating the age of the universe. He studied the spectrum of light from different heavenly bodies and found that this spectrum is moving towards the end of the red colour. Since light consists of electromagnetic waves, this spectral shift is a manifestation of the Doppler effect and indicates that all the celestial bodies are moving away from one another.

The Doppler effect refers to changing the frequency with which we perceive the waves when the object that emits them approaches or departs from us. We feel this effect when we are in the vicinity of a locomotive that whistles. When the locomotive approaches, the acoustic waves arrive at a higher frequency, so the sound is shifted to the more acute side of the range. After the locomotive has gone and gone, the waves arrive at a lower frequency, so the sound is shifted to the worst side of the range. Knowing the resting frequency of the locomotive’s whistle, an observer can realize without looking at whether the locomotive is approaching or moving away. Moreover, with sufficiently precise instruments, he can even measure the speed of the locomotive.

Light waves are subject to the same Doppler effect. If a star moves away, the frequency of the waves decreases, so the light moves to red. If the star approaches, the frequency of the waves increases and the light that it emits appears shifted to the purple. Hubble has discovered that the spectrum of the world from stars is shifted to red, which means that everything is moving away from the earth. It should not create the false impression that the earth would be the centre of this movement.

The relativistic Doppler effect, in two spatial dimensions, where the observer and emitter move with relative velocity V as shown, and the circles are wavefronts each a cycle apart. The medium the waves propagate through is stationary relative to the emitter. Left: In the emitter’s frame, the wave has frequency ν′ propagates with wave velocity s′, measured in the direction shown with the magnitude equal to the speed of propagation. The observer will appear to move with velocity −V. Right: In the observer’s frame, the emitter will appear to move with velocity V, the frequency ν increases during the approach to the observer, and the wave velocity s is given by the relativistic velocity addition formula. Wikipedia

Hubble has discovered that the speed at which a body moves is proportional to the distance to that body. This proves that it is uniform inflation of the space, somewhat similar to the inflation of a balloon, on which all the stains on its surface are evenly spaced from the cavities, without a point on the sphere that is the centre of this movement. The conclusion is inevitable: the universe is in a state of inflation whose speed can be calculated and described by physics equations. But these equations have an interesting property that gives us the opportunity to study the movement of the universe by reversing it, as a film can be reversed and viewed from a certain moment to the beginning.

In the case of the inflation of the universe, the laws of physics allow us to calculate not only the age of the universe but also how that beginning began. This was the idea of the Big Bang, which states that all matter and space itself would have been concentrated in an infinitesimal volume. Moreover, it is possible to calculate the energies and forces that have occurred and the reactions between the elementary particles at the twentieth second after the start of the Big Bang process. It was thus possible to calculate that the resulting substances were hydrogen (approximately 80%), helium (about 20%) and lithium, and they only appeared 377,000 years after the Big Bang before they -existing stable atoms.

It could be calculated that the first stars appeared about 300 million years after the Big Bang, following the collapse of hydrogen and helium clouds under gravity. The theory of inflation in the universe is not a speculative theory (such as the one about the existence of UFOs), but one based on accurate observations, measurements and calculations. Its precision was confirmed spectacularly in 1964 by the discovery of background cosmic radiation by two engineers working at Bell Labs in New Jersey, USA.

The theory of inflation predicted the existence of this radiation and calculated its intensity as being equivalent to a temperature of about 4 degrees Kelvin. What two engineers, Arno Penzias and Robert Wilson, who were experimenting with a certain kind of antenna, found that trying to capture radio signals could not eliminate a certain “noise” that came with the same intensity from all directions of the universe. The astrophysicists later confirmed that this “noise” was precisely that background radiation predicted by the universe’s theory of inflation, and with the same intensity as the predicted.




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