Thursday, April 30, 2009

GRB 090423

Ooooh! Yesterday's APOD shows the afterglow of gamma-ray burst 090423 which has a measured redshift of 8.2 -- making it the most distant GRB detected and (apart from the CMB) the most distant object ever observed. (090423 is also coincidentally our 10-year dating anniversary.)

For non-astronomers, redshift (or z) is the stretching of light-waves by the expansion of the universe; astronomers use it as a convenient shorthand for distance. Until recently you almost never saw anything beyond a z of 5, so a redshift of 8.2 is sort of like hitting 100 home runs in a season -- pretty cool! This burst arose from the death of a massive star back in the very, very early universe.

The rarity of high-z objects is partly because the bulk of the emitted light is shifted into the infrared (which is more of a pain to detect) and partly because neutral hydrogen absorbs much of the visible light past a certain redshift. In theory, objects like this one can tell us a lot about the era of reionization and the formation of structure in the universe. No doubt telescopes with infrared detectors are trying to squeeze every last photon out of this event.

If anyone is interested, you can follow the observation reports for this event -- from the initial detection by Swift to the discovery of the NIR afterglow -- at GRBlog or Jochen Greiner's website.

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