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The afterglow, redshift and extreme energetics of the γ-ray burst of 23 January 1999

Kelson, D. D.; Malkan, M. A.; Harrison, F. A. +26 more

Long-lived emission, known as afterglow, has now been detected from about a dozen γ-ray bursts. Distance determinations place the bursts at cosmological distances, with redshifts, z, ranging from ~1 to 3. The energy required to produce these bright γ-ray flashes is enormous: up to ~10 ⁵³erg, or 10 per cent of the rest-mass energy of a n…

Accretion of low-metallicity gas by the Milky Way

Savage, B. D.; Wakker, B. P.; Peletier, R. F. +7 more

Models of the chemical evolution of the Milky Way suggest that the observed abundances of elements heavier than helium (`metals') require a continuous infall of gas with metallicity (metal abundance) about 0.1 times the solar value. An infall rate integrated over the entire disk of the Milky Way of ~1 solar mass per year can solve the `G-dwarf pro…

Spectroscopic identification of a galaxy at a probable redshift of z = 6.68

Chen, Hsiao-Wen; Lanzetta, Kenneth M.; Pascarelle, Sebastian

The detection and identification of distant galaxies is an important goal of observational cosmology, as such galaxies are seen at a time when the Universe was very young. The development of new techniques and instrumentation permits the search for ever-fainter galaxies, and so aids attempts to determine when the first stars and galaxies formed. H…

A distance to the galaxy NGC4258 from observations of Cepheid variable stars

Zepf, Stephen E.; Davis, Marc; Madore, Barry F. +5 more

Cepheid variable stars pulsate in a way that is correlated with their intrinsic luminosity, making them useful as `standard candles' for determining distances to galaxies; the potential systematic uncertainties in the resulting distances have been estimated to be only 8-10%. They have played a crucial role in establishing the extragalactic distanc…

Stability of Neptune's ring arcs in question

Schneider, Glenn; Dumas, Christophe; Terrile, Richard J. +2 more

Although all four of the gas-giant planets in the Solar System have ring systems, only Neptune exhibits `ring arcs'-stable clumps of dust that are discontinuous from each other. Two basic mechanisms for confining the dust to these arcs have been proposed. The firstrelies on orbital resonances with two shepherding satellites, while the second invok…