What is a star?
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Updated June 01, 2013
A star is a aster like the sun shining through nuclear reactions that occur in the middle.
With the exception of the Sun, the stars appear to the naked eye as a bright, shimmering due to atmospheric turbulence, with no immediate apparent motion relative to other fixed objects in the sky. All the stars are considerably farther from Earth than the Sun. The nearest star, Proxima Centauri, is located about 4 light years of the solar system, nearly 250 000 times further away than the Sun.
The mass of a star is of the order of 1030 kg and its radius of the order of several million kilometers.
The power radiated by a star like the Sun is about 1026 watts. The stars are formed following the contraction of a nebula of gas and dust under the influence of gravity.
If the heating of the material is sufficient, this triggers the cycle of nuclear reactions in the heart of the nebula to form a star. The energy from these reactions is then sufficient to stop the contraction due to the radiation pressure generated.
The number of stars in the universe is estimated between 1022 and 1023. Apart from the Sun, the stars are too faint to be observed in daylight.
Image: Birth of a star, image made from data of X-ray telescope Chandra (blue) and data from the Spitzer Infrared Telescope (red and orange). nota: The astronomers classify stars in dwarf or giant.
At about 4 000 light years from Earth lies RCW 108, a region of the Milky Way where star formation is active where the presence of clusters of young blue stars in the image.
The one we saw the birth, in yellow at the center of the image is deeply embedded in a cloud of molecular hydrogen.
According to data from different telescopes, astronomers determined that star birth in this region is triggered by the proximity effect of massive young stars.
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Neutron stars are very small but very dense (1 billion tons per cubic centimeter). They concentrate the mass of a star like the Sun in a radius of about 10 km, corresponding to what is called the Chandrasekhar mass. These are the remnants of very massive stars with more than ten solar masses.
When a massive star reaches the end of existence, it collapses on itself, producing an impressive explosion called a supernova. The explosion dispersed large amounts of matter in space savings, but the heart of the star. The heart contracts and becomes largely a neutron star. These objects, called magnetars, have very strong magnetic fields. Along the magnetic axis spreads charged particles, eg electrons that produce synchrotron radiation.
If it turns quickly on its own when it projects along its magnetic axis a thin brush of radiation, it is then called "pulsar".
Image: IC 443 follows a stellar explosion, the ultimate fate of massive stars. In this false color composite image, we see the remains of the supernova still vibrating across the radio spectrum (blue), optical (red) and x-rays (green).
IC 443 is also known as the Jellyfish nebula, the image covers about 65 light years. IC443 is located at the estimated distance of 5000 light years. Credit image: Chandra xray
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