GRB's per galaxy

  • Thread starter granpa
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  • #1
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Main Question or Discussion Point

GRB's occur once per day. over 10 billion years thats 3650 billion bursts (in the observable universe?). I think there are said to be around 100 billion galaxies in the observable universe so does that mean that 36 bursts occur in each galaxy?

http://www.faqs.org/faqs/astronomy/faq/part8/section-4.html

I wonder how large a galaxy has to be before it has a supermassive black hole?

I wonder how many globular clusters there are and how that compares to the number 3650 billion?
 
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Answers and Replies

  • #2
Chronos
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GRB's are high redshift events [the nearest suspect occured at a distance estimated at over 30 Mpc], meaning they are relics of the distant past. Scientists believe hypernova are responsible for most GRB's. They are thought to arise from enormous, pristine [little or no metallicity] Pop I stars. Such stars do not exist in the Milky Way, or other nearby galaxies [gas clouds are too heavily polluted]. The rate of occurence is thought to be time dependent [frequency steadily decreases as universe ages].
 
  • #3
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30 megaparsecs is only 100 million lightyears.
 
  • #5
Chronos
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Indeed, 30 Mpc is z~.1 which is a little too close for comfort to support the hypernova hypothesis. It is suspected more exotic mechanisms may also exist, such as binary neutron star mergers. No one is quite sure what might happen in those cases, but, they are rare events. High redshift hypernova's, however, reasonably account for the vast majority of GRB's. Cosmology is always full of surprises and outlier observations evoke a great deal of interest. Most scientists take a wait and see attitude when a rogue observation contradicts reasonably well established theories. Many explanations are possible. Unfortunately the resources necessary to validate [or invalidate] them are precious and most researchers are unwilling to gamble their grant money on hitting a home run. It's the nature of the beast. The need to conduct daring experiments is often obviated by more mainstream studies. Clever scientists find ways to squeeze exotic information from these more 'mainstream' studies - a low risk, high reward opportunity. They are fond of referring to this as serendipity [a technobable term meaning 'lucky guess'].
 
  • #6
Hello Chronos and granpa,

A few comments.

There are two types of GRB's, long bursts and short bursts ( > few seconds and < few seconds respectively). The hypernova model only attempts to explain long GRB bursts. Hypernova are not necessarily stars formed early in the universe ( Chronos had a typo, he meant the early pristine stars are population II or III stars), they are just really massive stars (rapidly spinning Wolf-Rayet stars).
 

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