* Astronomy

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GRB 090423

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Title: GRB 090423 reveals an exploding star at the epoch of re-ionisation
Authors: R. Salvaterra, M. Della Valle, S. Campana, G. Chincarini, S. Covino, P. D'Avanzo, A. Fernandez-Soto, C. Guidorzi, F. Mannucci, R. Margutti, C.C. Thoene, L.A. Antonelli, S.D. Barthelmy, M. De Pasquale, V. D'Elia, F. Fiore, D. Fugazza, L.K. Hunt, E. Maiorano, S. Marinoni, F.E. Marshall, E. Molinari, J. Nousek, E. Pian, J.L. Racusin, L. Stella, L. Amati, G. Andreuzzi, G. Cusumano, E.E. Fenimore, P. Ferrero, P. Giommi, D. Guetta, S.T. Holland, K. Hurley, G.L. Israel, J. Mao, C.B. Markwardt, N. Masetti, C. Pagani, E. Palazzi, D.M. Palmer, S. Piranomonte, G. Tagliaferri, V. Testa
(Version v2)

The observation of the very early stages of the Universe represents one of the main challenges of modern cosmology. 200-300 million years after the Big Bang stars began to form, thus providing the Universe with the first sources of light and heat after the Big Bang. This event marks the transition between the epoch when the Universe was dark and neutral and the time when the Universe became fully ionised. The direct investigation of this cosmic epoch, usually accomplished by observing distant quasars, has been revolutionized in the last decade through the study of Gamma-ray Bursts (GRBs). GRBs are gamma-ray flashes, detected from space, produced by rare types of massive stellar explosions. Their rapidly fading afterglows are often bright at optical wavelengths, such that GRBs are detectable up to cosmological distances. Here we report on the Swift observation of GRB 090423 and the near-infrared spectroscopic measurement of its redshift z=8.1^{+0.1}_{-0.3} obtained with the Telescopio Nazionale Galileo (TNG). This GRB was produced in a cosmic explosion that occurred before the re-ionisation process was completed, when the Universe was only ~4% of its current age. Unexpectedly, this primordial object exhibits properties similar to those of GRBs observed at low/intermediate redshifts, indicating that the mechanisms and progenitors which gave rise to GRBs about 600 million years after the Big Bang are not markedly different from those producing GRBs ~10 billion years later. The detection of this GRB at z=8.1 indicates either that the GRBs are not good tracers of the cosmic star formation or that the number of bright GRBs was greater at high redshift.

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The discovery of the most remote star known to man opens a new window over one still unexplored period of history of our Universe: that of the formation of first stars and the first galaxies which led to the Universe which we currently know. For a few years the astrophysicists had hoped to discover explosions of massive stars in the very young universe (between 400 and 700 million years). This period of the life of our Universe is particularly interesting because it corresponds to the formation of first stars and galaxies which illuminated the cosmos after one long dark ages period. Such explosions, called "gamma ray bursts" , occur when the core of a star of more than 20 solar masses collapses into a black hole which swallows the central parts of the star in a few seconds and expels a jet of matter at speeds close to that of the light. The gamma bursts are composed of two phases: an intense flash of x-rays and gamma produced at the very moment of the explosion and a residual emission in all of the electromagnetic spectrum produced by the shock of the matter jet on the interstellar environment. The gamma bursts are observed regularly by the Swift satellite of NASA which alerts the observatories on the ground which can thus study the residual emission to measure the distance and energy of the explosion and to find the galaxy in which it is produced. The extreme luminosity of the gamma ray bursts makes it possible to detect them until in the most distant reaches of the Universe.

At 7:55 on the 23rd April, 2009, the NASA Swift satellite detected a 10 seconds duration flash of gamma rays that it quickly located. This event was named GRB 090423, (GRB for " Burst" gamma-Ray;) followed by the date on which the burst was detected.

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GRB 090423 with a a redshift of 8.2 is now officially the oldest and most distant known object in the Universe.
GRB 090423 exploded about 600 million years after the Big Bang.
The object replaces the previous record holder, GRB 080913, with a redshift of 6.7 (placing it 800 million yeas after the big bang).
Another distant object, a galaxy called I0K-1 was confirmed spectroscopically with a redshift of 6.964. The galaxy lies so far away that astronomers are seeing it as it appeared 12.88 billion years ago.

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GRB090423

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RE: GRB 090423

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The Gemini Observatory has released the first colour image of what astronomers are calling the most distant object ever seen in the universe. The object is what is known as a Gamma-ray burst (GRB) which are the most energetic single events known in the universe.

"Our infrared observations from Gemini immediately suggested that this was an unusually distant burst, these images were the smoking gun. The visible light was completely absorbed by hydrogen gas in the early universe, but the GRB was brightly glowing in the infrared images from Gemini" - Edo Berger, a leader in the scientific team that made the discovery and professor at Harvard Smithsonian Centre for Astrophysics.

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Universe: astronomers observe distant gamma-ray burst in Leo

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ESO's Very Large Telescope has shown that a faint gamma-ray burst detected last Thursday is the signature of the explosion of the earliest, most distant known object in the Universe (a redshift of 8.2). The explosion apparently took place more than 13 billion years ago, only about 600 million years after the Big Bang.
Gamma-ray bursts (GRBs) are powerful flashes of energetic gamma-rays lasting from less than a second to several minutes. They release a tremendous amount of energy in this short time making them the most powerful events in the Universe. They are thought to be mostly associated with the explosion of stars that collapse into black holes.

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The cataclysmic explosion of a giant star early in the history of the Universe is the most distant single object ever detected by telescopes.
The colossal blast was picked up first by Nasa's Swift space observatory which is tuned to see the high-energy gamma-rays emitted from extreme events.
Other telescopes then followed up the signal, confirming the source to be more than 13 billion light-years away.
Scientists say the star's destruction probably resulted in a black hole.

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NASA's Swift satellite and an international team of astronomers have found a gamma-ray burst from a star that died when the universe was only 630 million years old, or less than five percent of its present age. The event, dubbed GRB 090423, is the most distant cosmic explosion ever seen.

"Swift was designed to catch these very distant bursts. The incredible distance to this burst exceeded our greatest expectations -- it was a true blast from the past" - Swift lead scientist Neil Gehrels at NASA's Goddard Space Flight Centre in Greenbelt, Md.

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Astronomers have spotted the most distant object yet confirmed in the universe a self-destructing star that exploded 13.1 billion light years from Earth. It detonated just 640 million years after the big bang, around the end of the cosmic "dark ages", when the first stars and galaxies were lighting up space.

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GRB 090423 is a gamma-ray burst (GRB) discovered by the Swift Gamma-Ray Burst Mission on April 23, 2009 at 07:55:19 UTC. It is the current record-holder as the event/object most distant from Earth, occurring at a redshift of z = 8.2.

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