The death of stars
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Updated June 01, 2013
Nebulae that show the death of a star are common, so that astronomers were able to study closely the various steps of this scenario, properly understood.
Our Sun is a star, neither too big nor too small.
It shines and warms us with the energy released by a thermonuclear reaction that converts its hydrogen into helium.
Every second, our sun converted 4.26 million tons of hydrogen into energy. At this rate, scientists estimate there is about 5 billion years our sun to burn all its hydrogen reserves.
Depending on their size, the stars will therefore die in different ways. So in 5 billion years our Sun begins to run out of hydrogen.
After that time his heart very heavy with helium produced during the past billion years, are beginning to shrink thereby increasing its internal temperature and the effect of partially revive the fusion of hydrogen near the heart.
The envelope of the star then expands under the effect of heat and the diameter of the sun reaches one hundred times its current diameter.
In the heart, the temperature becomes high enough that the helium fuses into carbon. Under these conditions, ignition of the material is explosive: it speaks of 'helium flash'.
Then, the carbon is converted into nitrogen, nitrogen with oxygen.
The volume of the star increases further, causing a drop in temperature on its surface.
The star resembles a huge glowing embers, the color tends toward red.
It's become a red giant.
The dying star known intense stellar winds and these winds push the material of the outer layers under the effect of radiation pressure exerted by light.
The fusion of helium is exhausted in 10 million years ago, leaving a heart rich in carbon and oxygen, nitrogen has almost entirely disappeared.
The residual layers of hydrogen and helium burn: the layer of helium releases energy by lighting which again pushes the hydrogen layer. When the shock is absorbed, the material drawn by gravity, then falls on the layers of helium. It compresses and warms up prior to absorb another shock and begin the cycle again. The giant after 500 million years, then comes to an end. The envelope of the star, very dilated and structured peel onions, crumbled quickly, exposing the inner layers hot.
A planetary nebula takes shape in layers of expanding gases leaving appear inside a white dwarf with a density of 1 million times greater than that of the star to start. 10 billion years later, the white dwarf cools, becomes a black dwarf, cold and finally extinguished. The stars make it heavier, more solid chemicals such as iron. When they grow, too, they exhaust the gases contained in their nucleus.
The latter remains hot while the upper layers are cooled, causing an explosion in the upper layers and their projection into space. This phenomenon has been observed from Earth, about 1000 years ago and the light emitted by the star was visible for several days. Although the upper layers have exploded, the Linux kernel, is heavier than ever.
According to its mass, it will become a neutron star (pulsar) or black hole. The former are sometimes so small and dense, they go unnoticed.
Only their gas jet emitted by instinct, is detectable by radio telescopes. As for black holes, observations that could make this phenomenon tell us they have so much gravitational pull that nothing can nearby, resist them, not even their own light, so they are invisible. Astronomers can detect their presence by agitation they cause around them.
Image: Material ejected during a supernova that occurred in 1054 and had been noted by the Chinese: a superposition of X-ray image (shown in blue) and visible (red). The size of the ring is about one light year.
Credit: X-ray: NASA / CXC / ASU / J. Hester et al. ; visible: NASA / HST / ASU / J. Hester et al.
Image: The Hubble Space Telescope has photographed the remains of a star shining in the planetary nebula, cataloged NGC 6369, with its center, the small dwarf star dying. The star radiates strongly in the ultraviolet wavelengths and contributes to the expansion of the nebula. The main ring of the nebula is about a light year in diameter. Oxygen, hydrogen and ionized nitrogen are colored respectively in blue, green and red. This nebula, called the Little Ghost Nebula, is located about 2000 light years from our solar system. The Little Ghost Nebula suggests the destiny of our Sun, which should produce its own planetary nebula in about 5 billion years. Credits: NASA
Death of NGC 2440
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On February 7, 2007, Hubble has photographed NGC 2440, thanks to his instrument WPFC 2 (Wide Field Planetary Camera).
The false colors indicate the molecules of the cloud of gas and dust. Hydrogen is coincident with the nitrogen in the same red, blue helium and oxygen in blue-green.
The material ejected is made light by the ultraviolet emission that remains of the central star.
Very dense, it has become a white dwarf.
That of NGC 2440 reaches a temperature of 200k Kelvin.
This beautiful image also shows the irregularity of the cloud suggests that multiple explosions.
NGC 2440 is a planetary nebula, that is to say, a gaseous envelope ejected violently by a dying star, which exploded when lack of fuel, the nuclear reactions have been sufficient to contain the force of gravitation.
The accuracy of the image taken by Hubble shows the complexity of the internal cloud, which suggests a chaotic structure, with areas heavily laden with material and other nearly empty.
This heterogeneity suggests that the star did not explode at once, but the dying star has undergone several cycles of contractions and explosions.
At every jolt, some of his material was found ejected, but in a different direction.
The dust that was present around the star has been blown and now form long streaks, the white dwarf central styling.
Image: The image is observed cons, false color by the Hubble instrument WPFC 2; the nebula NGC 2440 shows a cloud of gas and dust which extends over a light year.
In the center, we identify the white dwarf, a remnant of the exploded star.
The cloud has an irregular and chaotic structure: the star has experienced several explosions that ejected matter in different directions by sculpting the columns of dust.
The red color shows the nitrogen and hydrogen, helium blue, green oxygen.
Credit: ESA/K. Noll (STScI).
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Massive stars can produce life directly in their periphery but they are responsible for the most basic foundations. Without them, neither carbon nor oxygen and other heavier elements could not exist. From the 76% hydrogen and 24% helium primitive, these stars have seeded the Universe with everything else we know. It is in their grand finale and a continuous mixing of nebulae increasingly loaded with heavy elements and complex than current stars of second and third generation have constituted solid planets where life has emerged.
So we are stardust, as Reeves said. It is troubling that nature constantly seeks the complexity in evolution. This consciousness within us that reasoning and thinking, is not material but yet need the biological substrate material and our brain to resonate.
Moreover it is our own or she crosses the whole thing?
Is the basis or the principle of the universe, its intention?
Inanimate things would you have a soul? In our insatiable curiosity, we seek to know and we want it to go back in time to Big Bang, there are approximately 13.7 billion years. The big question now scientists and astrophysicists is what was there before. Given this uniqueness, this quantum fluctuation where time stops and the laws of physics disappear, it is almost certain that we will never have any other answer than unverifiable conjecture. We thus see that these major scientific issues have become philosophical, even metaphysical, since the great philosophical questions now become metaphysical or scientific.
Image: The giant particle detector Atlas LHC could discover new elementary particles like the Higgs boson, a particle vainly sought to date, find super symmetric particles or access to extra dimensions of space. Credit: CERN
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