hurricanemaxi
Joined: 17 Sep 2011
Posts: 83
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 Posted: Sat Sep 17, 2011 11:03 pm Post subject: Gamma-Ray Bursts Shed Light On the Nature of Dark Energy |
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Dark energy is the basic constituent of the Universe today, one that is responsible for its accelerated expansion. Although astronomers observe the cosmological effects of the impact of dark energy, they still do not know exactly what it is. A new method for measuring the largest distances in the Universe developed by scientists from the Faculty of Physics, University of Warsaw and the University of Naples Federico II helps solve the mystery. A key role is played by the most powerful cosmic explosions -- gamma-ray bursts.
What is the nature of dark energy, a recently discovered dominant constituent of the Universe today? Is expansion-accelerating dark energy an intrinsic property of space-time itself or rather a field unknown to science? A new distance-measuring method developed by scientists from the Faculty of Physics, University of Warsaw (FUW) and the University of Naples Federico II can provide the answer. "We are able to determine the distance of an explosion on the basis of the properties of the radiation emitted during gamma-ray bursts. Given that some of these explosions are related to the most remote objects in space that we know about, we are able, for the first time, to assess the speed of space-time expansion even in the relatively early periods after the Big Bang," says Prof. Marek Demiański (FUW). The method was used to verify models of the structure of the Universe containing dark energy.
In 1998, during the analysis of the brightness of Type Ia supernovae, it was discovered that the most remote explosions seemed to be too weak. Type Ia supernovae appear in binary systems. One of the stars is a white dwarf, a relic of an evolutionary cycle of stars similar to the Sun. When the second star of the system enters the red giant phase and swells up, its external layers, containing mainly hydrogen, begin to fall onto the white dwarf, which gradually grows in mass. When the white dwarf reaches 1.4 solar masses, it explodes and is completely torn apart. Since the conditions that trigger the explosion are similar every time, Type Ia supernovae always release more or less the same amount of energy. Astronomers rely on this property to measure distances in space.
The fainter brightness of remote Type Ia supernovae was a clear indication that they were even more distant than assumed. Instead of slowing down the expansion, the Universe was accelerating. A new form of mass-energy -- dark energy -- needed to be introduced into the theory in order to reconcile the previous models of the Universe with the observations. The calculations indicate the existence of a huge amount of dark energy, nearly 20 times greater than the amount of mass-energy related to the world accessible to human senses. "Overnight, dark energy became, quite literally, the greatest mystery of the Universe," says Prof. Demiański.
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