From: Andy Soos, ENN
Published March 24, 2010 05:00 PM

The Edge of Space and Time

Alpha Centauri is the closest star to our solar system and is 4.3 light years away. If it disappeared it would take 4.3 years for us humans to notice the difference, Looking up into the sky is looking at a what happened long, long ago. Theoretically one can look all the way back to the Big Bang moment.

As telescopes become ever more powerful, we are able to observe objects closer and closer to the Big Bang. It is believed that the first stars formed when the Universe was very young – between 200 and 400 million years old – and the nearest we have got to seeing them so far is 630 million years from the Big Bang, when the Universe was less than five percent of its current age. The not so elegantly named ‘GRB 090423’ was discovered there, making it the most distant object yet seen in the Universe.


The burst occurred when the universe was approximately one twentieth of its present age. Prior to the observations done on GRB 090423, the previous record holder for age and distance was GRB 080913, which was observed in September 2008. That burst had a redshift of 6.7, placing it approximately 190 million light years closer to Earth than GRB 090423.

“GRB 090423 is an example of a gamma ray burst, the brightest and most violent explosions in the Universe,” explains Bremer, who was involved in the observations. “The explosion, which only lasted a matter of seconds, is thought to have accompanied the catastrophic death of a very massive star. It would have been triggered by the center of the star collapsing to form a black hole.”

A gamma ray burst is an extremely luminous flash of gamma rays that occurs as the result of an explosion, and is thought to be associated with the formation of a black hole. The burst itself typically only lasts for a few seconds, but gamma ray bursts frequently produce an afterglow at longer wavelengths that can be observed for many hours or even days after the burst.

Specifically, the progenitor star appears to belong to the second or third generation of stars, rather than the very first generation. The earliest stars are thought to have been massive, short lived balls of hydrogen and helium, whereas their offspring incorporated heavier elements formed in the first generation's explosive demise. The burst and afterglow of GRB 090423 is not unlike that of closer (and hence more recent) gamma ray bursts, pointing to a later generation progenitor.

GRB 090423 was discovered on April 23, 2009 by a robotic spacecraft called Swift that was launched into orbit in 2004. The discovery of such a distant gamma ray burst confirms that massive stellar births – and deaths – occurred in the very early Universe. Gamma ray bursts release a tremendous amount of energy in a very short time, but despite GRB 090423’s brief appearance, light from the explosion still managed to get here even though it took more than 13 billion years (which is at least 13 billion light years).

Light years are a convenient shorthand to describe the vast distances to these objects, telling us how long their light has been traveling to reach us, the Universe has been expanding during that whole period, so the Earth and these objects are now even further apart than they were when the light we see was first emitted. The object is even further away than 13 billion light years which is already an incredible number to imagine.

In comparison the furthest visible stellar object to the naked eye is generally considered to be the Andromeda galaxy which is only 2.5 million light years away. GRB090423 is quite a bit further away.

Galaxy clusters are the largest gravitationally bound objects in the Universe and at a distance of 10.2 billion light years, JKCS041 – the most distant galaxy cluster yet discovered – beats the previous record holder by about a billion light years. It sits on the cusp of the distance limit expected for a galaxy cluster, as physicists believe gravity could not have worked fast enough for them to cluster together much earlier. By studying the vicinity of GRB 090423 even earlier and further clusters or proto galaxies may be found.

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