Search Publications
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…
Discovery of a massive equatorial torus in the η Carinae stellar system
de Graauw, Th.; Waters, L. B. F. M.; Mutschke, H. +10 more
The enigmatic object η Carinae is believed to represent an important, but short-lived, unstable phase in the life of the most massive stars, occurring shortly before they explode as supernovae or collapse directly to black holes. The putative binary system believed to constitute η Carinae survived an outburst in the previous century that lasted 20…
Disappearance of stellar debris disks around main-sequence stars after 400 million years
Kessler, M. F.; Siebenmorgen, R.; Metcalfe, L. +7 more
Almost 5 billion years ago, the Sun formed in a local contraction of a cloud of molecular gas. A rotating disk of gas and dust is believed to have fed material onto the proto-Sun for the first few million years of its life, and to have formed the planets, comets and other Solar System objects. Similar disks, but with less mass, have been observed …
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…
Discovery of molecular hydrogen in a high-velocity cloud of the Galactic halo
de Boer, K. S.; Grewing, M.; Richter, P. +4 more
The Milky Way's halo contains clouds of neutral hydrogen with high radial velocities which do not follow the general rotational motion of the Galaxy. Few distances to these high-velocity clouds are known, so even gross properties such as total mass are hard to determine. As a consequence, there is no generally accepted theory regarding their origi…
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…
Discovery of a supernova explosion at half the age of the Universe
Panagia, N.; Lidman, C.; Aldering, G. +19 more
The ultimate fate of the Universe, infinite expansion or a big crunch, can be determined by using the redshifts and distances of very distant supernovae to monitor changes in the expansion rate. We can now find large numbers of these distant supernovae, and measure their redshifts and apparent brightnesses; moreover, recent studies of nearby type …
An unusual supernova in the error box of the γ-ray burst of 25 April 1998
Piro, L.; Pian, E.; Palazzi, E. +46 more
The discovery of afterglows associated with γ-ray bursts at X-ray, optical and radio wavelengths and the measurement of the redshifts of some of these events, has established that γ-ray bursts lie at extreme distances, making them the most powerful photon-emitters known in the Universe. Here we report the discovery of transient optical emission in…
X-ray flare sparks quake inside Sun
Kosovichev, A. G.; Zharkova, V. V.
Solar flares involve a release of the Sun's magnetic energy as X-radiation, particle beams and high-speed plasma flows. But we have discovered, using data from the Solar and Heliospheric Observatory (SOHO), that these flares also affect the Sun's interior, generating seismic waves similar to earthquakes. For example, a three-kilometre-high seismic…