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How big are the stars?

26 Oct

big starsShimmering Stars seem tiny points of light, but in reality, they are huge. Astronomers do not know exactly how big can become a star, but in certain circumstances, it seems, they can be truly enormous. The nearest star – is, of course, the sun. It has a weight of about 2 million trillion trillion kilograms (two and thirty zeros after it). If the Earth were weighed as a paper clip, the Sun would weigh like a motorcycle Ural.

Although the sun is not so easy, and in fact the weight of a little above average. About 1% of the stars weigh eight times larger than the Sun, and the sheer handful of stars in the galaxy weighs as much as one or two hundred suns.

The most massive star known – R136a1 – weighs about 265 solar masses. It is so huge that its discovery in 2010 prompted astronomers to revise their theories of how massive a star can be. This, in turn, leads us to revise our understanding of the first stars that were once formed. It turns out that some of the first stars born after just 200 million years after the Big Bang, might weigh 100, 000 times that of the Sun, making them the most massive stars in principle. The question is how these primary R136a1 star general could be so big?

The mass stars – not just an interesting quantity. This is the most important property of stars, which determines how the star lives and dies. Star – is a giant ball of hot gas is so massive that its gravity pulls him to her. As a result, the core of the star becomes extremely dense and hot. This triggers nuclear reaction in which a pair of atoms coalesce to larger, producing a lot of heat and pressure, which pushes back the star outward.

The life of the stars hanging in the balance between gravity and pressure. As soon as the fuel, fusion stops and cannot prevent the collapse. The fate of the star and its rate of burn is completely dependent on its mass. Massive stars of several tens of solar masses burn fast and bright. They live only a few hundred million years before exploding into a supernova and retain dense, exotic objects such as black holes or neutron stars. In contrast, small stars like the Sun burn slowly and steadily for millions of years before becoming a stellar corpse – white dwarfs.

The smallest star can be 0.08 solar mass, based on the relative certainty and simple calculations. Star is such a mass of massive enough to start nuclear fusion. Anything less will be a ball of gas. But if astronomers are well aware of the minimum mass of the star at the other end all blurry. This is one of the biggest unsolved mysteries of astrophysics, – says Volker Bromma, an astrophysicist at the University of Texas at Austin, USA.

Ten years ago, astronomers thought that the upper limit of stellar masses in the current universe of 150 solar masses. There were a lot of good evidence to support this limit, as the theory and observation of, – says Paul Krauter of the University of Sheffield in the UK. You must be lucky that you saw the star of high mass, because their lifespan is very short. Stars of a hundred or more solar masses die in a couple of million years: an instant on space standards.

One of the most promising places to look for such a star – Arches cluster is one of the densest collections of stars in the Milky Way. This cluster seemed to have formed relatively recently, since the most massive stars are still alive. Around him lying as much material for star formation, ensuring an environment conducive to stellar giants. But astronomers have not been able to find a star with a mass greater than 150 solar. Perhaps, they thought, the stars just cannot be so massive.

At some point, a star must be so massive and bright that it blows away the outer layers of radiation, preventing further growth. This natural weight limit is called the Eddington limit, and calculations suggest that it is close to 150 solar masses. But in 2010, a group of astronomers and Krauter studied even heavier stars in the cluster group of R136. There they found not one, but even a few stars, surpassed the limit of 150 solar masses. The most surprising, that R136a1, was incredible mass of 265 solar.

Moreover, perhaps it was even heavier when born.R136a1 – Star Wolf – Rayet star, which means that it is a massive, bright and hot, with a powerful radiation, which blows off its outer layers. Its temperature of about 53,000 degrees Celsius, and it shines 10 million times brighter than the sun. Even though she is young, barely more than a million years old, she has already lost 50 of our gas Suns.

From which it follows that R136a1 once weighed more than 300 suns. Much more than the limit of 150 solar masses. Exceeding this limit was not a problem. Previous estimates Eddington luminosity were relatively crude, said Krauter, and more detailed calculations showed that the stars can be much more massive – in theory, at least.

With regard to cluster Arches, astronomers have discovered that it is older than previously thought and really massive stars have long since ceased to exist. R136, however, is much younger than the original stars. Whatever it was, heavyweights like R136a1 – a rarity. In the Milky Way there could be very little, says Krauter. The biggest question is how they scored a lot of – he says. To a growing star gained weight, it takes time. Stars like the Sun should be about 10 million years to education. But stars like R136a1 live only a few million years, so they must have been formed hundreds of thousands of years ago.

Nobody knows for sure. One idea is that these huge stars are formed when faced long filaments of cold and dense gas. Over the past couple of years, the Herschel Space Observatory in Europe has found such filaments across the galaxy. Each pulled a few light years. When these strands are facing each other, may form dense volumes of gas that collapse into a star, giving life to a whole star cluster at the same time. Most of these new stars will be small, some massive, and even less like the giant R136a1.

It is difficult to understand how this happens. Details fairly blurred, I would say, – said Krauter. These regions of massive star formation hidden dense clouds of interstellar dust, so even the most powerful telescopes can barely get through them. The giant stars may also be formed when the stars merge. Most of the heavy stars are in pairs, one way or another, so if a couple of these stars will have a mass of several tens of times greater than the sun, they can merge into one big star. As stars like R136a1 become so large, it remains a mystery, but the very first stars surprise even more. They are truly enormous.

After 200 million years after the Big Bang was a lot of light. When the clouds of hydrogen and helium gas to collapse into the first stars of the universe. Unlike today’s stars, they were much more massive. Many weigh tens of solar masses, some reaching hundreds or two. Those first stars could reach it, as the space environment was different. In particular, there was no heavy chemical element. Heavy elements are important because they help to cool gas clouds. The hot gas atoms flicker back and forth and collide with each other. Heavy elements can transform this collision energy into light, which would then be rejected. So goes the heat.

But the heavy elements are not always existed. They were forged from nuclear fusion in the cores of stars and in the explosive deaths of massive stars. Generation after generation, the star made all the elements that we find in space today. When the first star in the world was only hydrogen, helium and a tiny fraction of lithium. Without the heavy elements, gas clouds cooled down with difficulty, and therefore they were harder to collapse into stars. To compensate for this, every cloud has grown more and more, gaining more than gravity to trigger the collapse.

As a result, born stars that are more massive than modern stars. For decades, no one knew for sure how it was massive. Recently, astronomers have come to the discovery that those stars can be much larger than previously thought. Astronomers have discovered quasars exist in a billion years after the Big Bang. Quasars – an extremely bright objects, which are fed black hole millions or billions of times the mass of the sun. A black hole is fed swirling disk of dust and gas, throwing out powerful beams of energy.

Black holes form when stars exhaust their fuel and collapse. To become a super massive black hole, it must absorb a lot of weight in the form of the nearest gas and dust, or merging with other black holes. The problem is that these quasars existed in this early history of the cosmos, which super massive black holes were to gain your weight in an incredibly short period of time. Based on theory and computer simulations, even the star of a few hundred solar masses would not have to grow up so quickly to become super massive.

There is a solution to this paradox, but it includes a really huge stars of 100 000 solar masses. Next to such stars even R136a1 would dwarf. Computer calculations show that the cloud of a million solar masses may collapse into a star with a mass of 100 000 suns. Conditions should also be suitable: no heavy elements and a lot of ultraviolet radiation, which further prevents the cooling of the gas cloud. The star of this size will be unstable and can instantly collapse into a black hole.

This black hole and then continue to increase their weight by consuming dust and gas, or merging with other black holes, until it becomes massive enough to feed the quasar. That is the theory. Our computers patiently create these objects, – says Alexander Heger of Monash University in Australia. – But do they exist in nature, we have no direct evidence of this. All are active theoretical point.

 
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Posted by on October 26, 2015 in Planet

 

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