- 3664 - STARS - why are they all about the same size? In wildly different environments, stars end up roughly the same? When you look at a region of the sky where stars are born, you see a cloud of gas and dust and a bunch of stars. In most places, the stars all end up being about the same mass.
--------------------- 3664 - STARS - why are they all about the same size?
- That stellar mass is probably the most important factor you want to know about a star. It directs how long the star will live and what its future will be like. But, what determines its mass and the mass of its siblings in a stellar nursery? Is there some governing force that tells them how massive they’ll be? It turns out that the stars do it for themselves.
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- Years of observations show that no matter where we look in our galaxy, stars in clusters have similar masses. They could be clusters of sun-like stars all the way up to groupings of massive stellar behemoths. And, this is true whether they’re hot and young in the modern epoch, or are billions of years old.
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- Astronomers wanted to know how that could be?
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- Astronomers have discovered that star formation is a self-regulating process. Stars that form in wildly different environments have a similar mass, because stellar feedback, which opposes gravity, acts differently, pushing stellar masses toward the same mass distribution.
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- This phenomenon is called ‘stellar feedback’ and it’s part of the self-regulating mechanism that governs the stellar masses. Stars are born in batches inside giant clouds of gas and dust. Over time, gravitational attraction pulls the dust grains together along with the gas. That forms dense clumps that falls inwards toward the center of the clouds and compresses them. As densities rise, temperatures rise. Eventually, a star is born.
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- Each star has a rotating disk of gas and dust around it, and that’s where planets can form. If they do, that raises the question of whether they can become life-supporting worlds.
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- Whether those planets could host life is dependent on the star’s mass and how it formed. Therefore, understanding the formation and the masses of the stars that get created in a given cloud is crucial to determining where life can form in the universe.
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- Stars are the atoms of the galaxy. Their mass distribution dictates whether planets will be born and if life could develop. The self-regulatory process of mass among newly forming stars isn’t just important to understand planet and life formation in our own galaxy. That knowledge can now be used to study other galaxies and help astronomers get a better handle on the same processes in distant galaxies.
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- Our Sun is the source of life on Earth. Its calm glow across billions of years has allowed life to evolve and flourish on our world. This does not mean our Sun doesn’t have an active side.
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- We have observed massive solar flares, such as the “1859 Carrington event“, which produced northern lights as far south as the Caribbean, and drove electrical currents in telegraph lines. If such a flare occurred in Earth’s direction today, it would devastate our electrical infrastructure. But fortunately for us, the Sun is mostly calm. Unusually calm when compared to other stars.
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- Astronomers have only recently studied the activity of the Sun. The oldest study, undertaken since the 1600s, follows counts the number of spots seen on the Sun’s surface. It has shown us that the Sun goes through cycles of active and quiet periods. A four-century study is long in human terms, but is barely a moment of cosmic time.
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- Longer studies have looked at isotopes of carbon and other elements in ice cores and tree rings. When the Sun is particularly active, high-energy protons can strike atoms in the upper atmosphere, converting them into radioactive isotopes. They can then become trapped in ice and wood. This gives us an idea of solar activity across nearly 10,000 years.
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- That is still only a fraction of the Sun’s lifetime. Is the past few thousand years a good sample of solar activity? What if the Sun just happens to be going through an unusually calm period, and is usually far more active?
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- Using data from the “Gaia spacecraft“, astronomers looked for stars very similar to the Sun. They found stars of similar mass, age, and surface temperature. From these they chose stars that not only had a similar metallicity, but also a similar rotational speed. They were left with 369 stars that are nearly twins of our Sun.
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- They then compared the Sun’s variation in activity over four years to the activity of these other stars. They found that the Sun’s activity is much lower than the others. The variability of other stars is five times stronger than our Sun. Solar flares such as the Carrington event are much more common on other stars.
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- This could mean that our Sun has been usually calm during the span of human civilization. If that’s the case, it could become more active in the future, which could have serious consequences for our civilization. It is also possible that there is some unknown factor that keeps our Sun so calm.
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- At the moment, there is no indication that the Sun might enter a hyperactive period. For now and for the foreseeable future we can continue to enjoy the calm of the Sun. But, we are entering a period of more solar flares. That lucky ol Sun got nothing to do but to roam around heaven all day and shoot flares at us.
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August 27, 2022 STARS - why are they all about the same size? 3664
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