Gamma Ray Bursts and the Volume of the Distant Universe

[Devil Particle]

I read somewhere that gamma ray bursts occur in the distant universe for some reason having to do with the early universe having a greater density or lower metalicity. I apologize becuase I don't recall the exact reason. But statistically wouldn't you expect that an event as rare as a gamma ray burst would be detected more often in the distant universe due to the volume of the distant universe being proportional the cube of the distance?

For instance, if you look within 1 billion light years (bly) from earth the volume would be 4/3 pi bly cubed. But if you look between 9 and 10 bly it would be 360 pi bly cubed. (approximately)

Is it possible that gamma ray bursts are just as likely to occur in the nearby universe (say in the virgo cluster) as in the distant universe?

[neufer]

I read somewhere that gamma ray bursts occur in the distant universe for some reason having to do with the early universe having a greater density or lower metalicity. I apologize because I don't recall the exact reason. But statistically wouldn't you expect that an event as rare as a gamma ray burst would be detected more often in the distant universe due to the volume of the distant universe being proportional the cube of the distance?

For instance, if you look within 1 billion light years (bly) from earth the volume would be 4/3 pi bly cubed. But if you look between 9 and 10 bly it would be 360 pi bly cubed. (approximately)

Is it possible that gamma ray bursts are just as likely to occur in the nearby universe (say in the virgo cluster) as in the distant universe?

No. Old galaxies (like the Milky Way and Virgo Cluster members) do not have very many extremely massive low-metallicity stars that would make good candidates for a gamma-ray burst source.

<<The most widely-accepted mechanism for the origin of long-duration gamma-ray burst sources is the collapsar model, in which the core of an extremely massive, low-metallicity, rapidly-rotating star collapses into a black hole in the final stages of its evolution.>>

<<Orbiting the Sun roughly 1.5 million kilometres from Earth, the Planck space-based telescope is scanning the sky for ultra-cold objects. The mission has also picked up what researchers believe to be light from some of the earliest galaxies in the Universe. The ubiquitous infrared glow covers much of the sky and seems to be emanating from galaxies that form 10–1,000 new stars a year. By contrast, the Milky Way forms just one new star a year.>>

Positions on the sky of all gamma-ray bursts detected during the BATSE mission. The distribution is isotropic, with no concentration towards the plane of the Milky Way, which runs horizontally through the center of the image.

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<<Because of the immense distances of most gamma-ray burst sources from Earth, identification of the progenitors, the systems that produce these explosions, is particularly challenging. The association of some long GRBs with supernovae and the fact that their host galaxies are rapidly star-forming offer very strong evidence that long gamma-ray bursts are associated with massive stars. The most widely-accepted mechanism for the origin of long-duration GRBs is the collapsar model, in which the core of an extremely massive, low-metallicity, rapidly-rotating star collapses into a black hole in the final stages of its evolution. Matter near the star's core rains down towards the center and swirls into a high-density accretion disk. The infall of this material into a black hole drives a pair of relativistic jets out along the rotational axis, which pummel through the stellar envelope and eventually break through the stellar surface and radiate as gamma rays. Some alternative models replace the black hole with a newly-formed magnetar, although most other aspects of the model (the collapse of the core of a massive star and the formation of relativistic jets) are the same.

The closest Galactic analogs of the stars producing long gamma-ray bursts are likely the Wolf-Rayet stars, extremely hot and massive stars which have shed most or all of their hydrogen due to radiation pressure. Eta Carinae and WR 104 have been cited as possible gamma-ray burst progenitors. It is unclear if any star in the Milky Way has the appropriate characteristics to produce a gamma-ray burst.

The massive-star model probably does not explain all types of gamma-ray burst. There is strong evidence that some short-duration gamma-ray bursts occur in systems with no star formation and where no massive stars are present, such as galaxy halos and intergalactic space. The favored theory for the origin of most short gamma-ray bursts is the merger of a binary system consisting of two neutron stars. According to this model, the two stars in a binary slowly spiral towards each other due to the release of energy via gravitational radiation until the neutron stars suddenly rip each other apart due to tidal forces and collapse into a single black hole. The infall of matter into the new black hole in an accretion disk then powers an explosion, similar to the collapsar model. Numerous other models have also been proposed to explain short gamma-ray bursts, including the merger of a neutron star and a black hole, the accretion-induced collapse of a neutron star, or the evaporation of primordial black holes.>>

[Devil Particle]

Thanks! I hadn't previously read the Nature article about the recent data from the Planck telescope. Very interesting stuff.

[bystander]

Thanks! I hadn't previously read the Nature article about the recent data from the Planck telescope. Very interesting stuff.

http://asterisk.apod.com/vie ... 17#p140917
http://asterisk.apod.com/vie ... 94#p140894

http://asterisk.apod.com/vie ... 31&t=22313