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GRB 090423: probably the birth of a black hole

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GRB 090423 is a gamma-ray burst (GRB) detected by the Swift Gamma-Ray Burst Mission on April 23, 2009 at 07:55:19 UTC.
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Two international teams of astronomers have reported their observations of what they refer to as the last blank space on the map of the Universe, namely, a gamma-ray burst from a star that died when the Universe was 640 million years old, or less than 5 percent of its present age.
Dubbed GRB 090423, the record-breaker is an example of the brightest and most violent explosions known to exist.

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Light coming to us from such a distance is stretched because the universe is expanding. The greater the stretching - called redshift - the more distant the object. The previous most-distant object, a galaxy, has a redshift of 6.96. GRB 090423 has a redshift of 8.2 and appears to observers as an extremely red point of light. When that explosion took place, the universe was more than nine times smaller than it is now.

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Astronomers have confirmed that an exploding star spotted by Nasa's Swift satellite is the most distant cosmic object to be detected by telescopes.
In the journal Nature, two teams of astronomers report their observations of a gamma-ray burst from a star that died 13.1 billion light-years away.
The massive star died about 630 million years after the Big Bang.


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Two teams have spied a huge blast from the far reaches of our early Universe. Such -ray bursts occur when certain massive stars violently explode. The latest burst happened a mere 630 million years after the Big Bang (that's 13.1 billion years ago) and is the youngest such blast to have been spotted - the previous record-beater happened 825 million years after the Big Bang.

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Most Distant Object Yet Detected Carries Clues from Early Universe
A violent explosion picked up by a NASA satellite earlier this year is the oldest object ever seen by astronomers, its light having been emitted some 13 billion years ago. At that time the universe was roughly 5 percent of its present age and the big bang was a fairly recent occurrence, having taken place just 600 million years earlier.


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Title: Discovery of Radio Afterglow from the Most Distant Cosmic Explosion
Authors: Poonam Chandra, Dale A. Frail, Derek Fox, Shrinivas Kulkarni, Edo BErger, S. Bradley Cenko, Douglas C.-J. Bock, Fiona Harrison, Mansi Kasliwal

We report the discovery of radio afterglow emission from the gamma-ray burst GRB 090423, which exploded at a redshift of 8.3, making it the object with the highest known redshift in the Universe. By combining our radio measurements with existing X-ray and infrared observations, we estimate the kinetic energy of the afterglow, the geometry of the outflow and the density of the circumburst medium. Our best fit model is a quasi-spherical, high-energy explosion in a low, constant-density medium. \event had a similar energy release to the other well-studied high redshift GRB 050904 (z=6.26), but their circumburst densities differ by two orders of magnitude. We compare the properties of \event with a sample of GRBs at moderate redshifts. We find that the high energy and afterglow properties of \event are not sufficiently different from other GRBs to suggest a different kind of progenitor, such as a Population III star. However, we argue that it is not clear that the afterglow properties alone can provide convincing identification of Population III progenitors. We suggest that the millimetre and centimetre radio detections of \event at early times contained emission from a reverse shock component. This has important implications for the detection of high redshift GRBs by the next generation of radio facilities.

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Scrambling to Read the Meaning Of the Sky's Most Ancient Flare
This spring, astronomers detected GRB 090423, the most distant gamma ray burst they had ever seen. Its redshift of 8.2 shows that it went off a mere 625 million years after the big bang, proving that the universe had already come alive with stars when it was less than 5% of its present age. GRB 090423's discovery and the ensuing race to publish observations offer a glimpse into 21st century astronomy - a high-stakes pursuit in which communications networks make possible worldwide, round-the-clock collaborations, and pressures for cooperation and competition often come into simultaneous play.


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