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Massive Neutron Stars vs. Black HolesBlack holes may not form as often as previously believed |
By Gabriel Gache, Science News Editor
15th of January 2008, 07:53 GMT
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The universe is practically littered with corpses of dead stars, or at least the visible part of the universe is. In fact, most of the matter forming the Earth comes from the bodies of one or more stars
that shed part of their material at the end of their lives. However, not all the stars come to share the same fate. Many of the more massive stars turn into neutron stars or black holes during the process of supernova explosion.
New findings of the Arecibo Radio Telescope argue that, in fact, the neutron stars could get more massive than the previous theories predicted, thus black holes may not form so often, as they would require an increased mass in order to determine the gravitational collapse of neutron stars.
The neutron stars are thought to be composed of a mix of nuclear constituents, mostly neutrons, in a state of super dense matter. Meaning that the average density inside a neutron star would in fact be higher than in the middle of an atomic nucleus. Just a spoon of matter in such a dense state would weigh about a few billion metric tonnes on Earth.
It is generally believed that a neutron star forms during the supernova phase of a massive star, determined by the lack of nuclear fuel inside it. As the star explodes, the top layers of the star are being ejected into the space. At the same time, the third law of motion, stating that an action must have an equal reaction, acts on the inner core of the star compressing it into a super-dense object. Usually, the theory predicts that the minimum amount of mass required to create a neutron star would average 1.4 the mass of the Sun, with a diameter ranging between 10 to 16 kilometers, the size of a relative large asteroid.
Until recently, it was suggested that black holes may be relatively abundant in the universe and about 30 percent of the total black holes population would be practically wandering alone through interstellar and intergalactic space. Nevertheless, the new observations carried out by the Arecibo Observatory, predicting increased masses for neutron stars, result in a natural presumption that black holes would not form so frequently as previously believed, thus their number must have been greatly overestimated.
Theoretical models of black holes formation reveal a minimum necessary amount of matter to form a black hole in the range of 1.6 to 2.5 solar masses. Astronomers from Arecibo, however, predict that a neutron star could maintain its state until it reaches a mass of about 1.9 to 2.7 times the mass of the Sun, so anything above this limit will ultimately result in a gravitational collapse.
For about six years, the Arecibo observatory has been studying a binary pulsar located in the globular star cluster known as M5. Light pulses emitted by the M5 B pulsar, received on the surface of the Earth with a period of about 8 milliseconds, corroborated with the orbital motion of the companion, have shown that the M5 B pulsar has an estimated mass of about 1.9 solar masses.
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