Search Publications
Near-coeval formation of the Galactic bulge and halo inferred from globular cluster ages
Gilmozzi, Roberto; Rich, R. Michael; Renzini, Alvio +4 more
THE morphology of our Galaxy is characterized by a disk of stars moving on circular orbits, surrounding a central spheroidal body of stars on high-velocity, randomly oriented orbits. The spheroid is further differentiated into an inner bulge and an outer halo; the bulge stars are rich in elements heavier than helium ('metals'), whereas the halo st…
Detection of an oxygen atmosphere on Jupiter's moon Europa
Feldman, P. D.; Strobel, D. F.; Weaver, H. A. +2 more
EUROPA, the second large satellite out from Jupiter, is roughly the size of Earth's Moon, but unlike the Moon, it has water ice on its surface1. There have been suggestions that an oxygen atmosphere should accumulate around such a body, through reactions which break up the water molecules and form molecular hydrogen and oxygen2,3
Determination of the Hubble constant from observations of Cepheid variables in the galaxy M96
Ferguson, H. C.; Tanvir, N. R.; Shanks, T. +1 more
New Hubble Space Telescope observations of Cepheid variable stars in the nearby galaxy M96 give a distance to the host galaxy group, Leo I, of 11.6 +/- 0.8 Mpc. This value, used in conjunction with several reliable secondary indicators of relative distance, constrains the distances to more remote galaxy clusters, and yields a value of the Hubble c…
Interacting elliptical galaxies as hosts of intermediate-redshift quasars
Boksenberg, A.; Crane, P.; Sparks, W. B. +7 more
QUASARS are the most luminous objects in the Universe. It has been speculated that they are the visible evidence for accretion of gas onto supermassive black holes that reside at the centres of host galaxies. Direct observational confirmation that quasars reside in the centres of galaxies has been hard to obtain, because atmospheric turbulence usu…
Detection of massive forming galaxies at redshifts z>l
Cowie, Lennox L.; Hu, Esther M.; Songaila, Antoinette
THE complex problem of when and how galaxies formed has only recently become susceptible to direct attack. It has been known for some time that the excess of blue galaxies counted at faint magnitudes1á¤-5 implies that a considerable fraction of the massive-star formation in the Universe occurred at redshift z < 3 (refs 6, 7); but sur…
Large size of Lyman-α gas clouds at intermediate redshifts
Morris, Simon L.; Weymann, Ray J.; Foltz, Craig B. +2 more
THE Lyman-α absorption lines observed in the spectra of quasars are thought to be caused by intervening clouds of atomic hydrogen, the origin and physical nature of which are still unknown. These clouds might be structures confined by the pressure of the surrounding intergalactic medium1, relicts of density fluctuations in the early Uni…
An ultraviolet flare at the centre of the elliptical galaxy NGC4552
Cappellari, Michele; Renzini, Alvio; Greggio, Laura +3 more
MOST present-day galaxies are not 'active', in that they show no signs of continuing, high-energy events. The high energy output of an active galaxy is usually attributed to accretion of gas onto a massive black hole at its centre. Yet it remains an open question whether such black holes might exist at the centre of most large galaxies, and be und…
Propagation of solar oscillations through the interplanetary medium
Lanzerotti, Louis J.; Thomson, David J.; Maclennan, Carol G.
Time-series analysis of the fluxes of interplanetary charged particles measured by the Ulysses and Voyager spacecraft reveals many periodic components. From 1 to 140 µHz, the spectral components are consistent with those estimated (but not confirmed) for gravity-mode oscillations of the Sun: from 1,000 to 4,000 µHz, the spectral lines closely matc…
Identification of faint radio sources with optically luminous interacting disk galaxies
Griffiths, R. E.; Fomalont, E. B.; Windhorst, R. A. +5 more
THE question of when galaxies and stars started to form in the early Universe is one of the most fundamental in cosmology. Faint radio sources (with fluxes of a few microjanskys or less) may be these early galaxies; radio surveys have shown them to be increasingly common as fainter levels are reached1-7, suggesting that they are an impo…
Extensive dark-matter haloes in low-luminosity galaxies revealed by quasar absorption lines
Barcons, X.; Webb, J. K.; Lanzettat, K. M.
STUDIES of the kinematics of spiral galaxies suggest that dark (possibly non-baryonic) matter is a significant component of their total mass1. It has been difficult to determine how far the dark-matter haloes of galaxies extend, however, because the presence of dark matter must be inferred from the motion of a luminous component such as…