Y-ray burst

Massive stars play a key role in the spectral evolution of galaxies, they are also the progenitors of Wo I f Rayet (WR) stars, supernovae and y-ray bursts. They are the main agents of nucleosynthesis driving the chemical evolution of galaxies. The relative numbers of the various kinds of massive stars (blue, red supergiants, WR stars), their properties and nucleosynthesis very much depend on mass loss and rotation, as well as on the interaction of these two effects. 

DLAs and other intervening absorption-line systems are also found projected against the visual afterglows of long-duration y-ray burst sources at high redshifts. 

X-ray and optical follow-up studies reveal origin of y-ray bursts in powerful extragalactic sources ( hypernovae ) at cosmological distances. 

The y-ray bursts emitted by supernovae generally consist of photons with energies less than about 3.0 10 electron volts (eV). Convert this energy to SI units, and calculate the wavelength and frequency of the radiation. 

The coalescence of a binary neutron star system in coincidence with a y-ray burst should allow researchers to test the origin of this process. A coalescing binary system can also be used as a standard candle, up to hundreds of Mpc. In fact, the measurement of the chirp time allows for deduction of the chirp mass and prediction of the signal intensity, thus determining the distance of the binary system. If an optical counterpart of the source is found, its redshift can be determined by classical methods. In this way, the Hubble constant can be determined. 

G. R. Burbidge gave a review paper on the Masses of Galaxies and the Mass-Energy in the Universe and Hofstadter presented the information available at the time on the recent discovery of bursts of -y-rays.111... 

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