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The formation and evolution of galaxies.
Ellis, Richard
Galaxies represent the visible fabric of the Universe and there has been considerable progress recently in both observational and theoretical studies. The underlying goal is to understand the present-day diversity of galaxy forms, masses and luminosities. Popular models predict the bulk of the population assembled recently, in apparent agreement w…
The optical counterparts of γ-ray bursts
Harrison, Thomas E.; McNamara, Bernard J.
The origin of γ-ray bursts-which are among the most energetic events in the Universe-has puzzled astronomers for 25 years. Since 1991, new events have been discovered at a rate of about one per day, but because their positions were poorly determined, the objects responsible for these outbursts could not be identified. Now, following the launch of …
Bi-directional plasma jets produced by magnetic reconnection on the Sun
Inhester, B.; Wilhelm, K.; Innes, D. E. +1 more
Magnetic reconnection, the process by which magnetic lines of force break and rejoin into a lower-energy configuration, is considered to be the fundamental process by which magnetic energy is converted into plasma kinetic energy1. The Sun has a large reservoir of magnetic energy, and the energy released by magnetic reconnection has been…
A subsurface flow of material from the Sun's equator to its poles
Scherrer, P. H.; Bogart, R. S.; Duvall, T. L. +1 more
Gas on the Sun's surface has been observed to flow away from the equator towards both poles. If the same flow persists to great depths, it could play an important dynamical role in the eleven-year sunspot cycle, by carrying the magnetic remnants of the sunspots to high latitudes. An even deeper counterflow, which would be required to maintain mass…
The optical counterpart to γ-ray burst GRB970228 observed using the Hubble Space Telescope
Livio, Mario; Kouveliotou, Chryssa; Sahu, Kailash C. +7 more
Although more than 2,000 astronomical γ-ray bursts (GRBs) have been detected, and numerous models proposed to explain their occurrence1, they have remained enigmatic owing to the lack of an obvious counterpart at other wavelengths2-5. The recent ground-based detection6,7 of a transient optical source in the vicinit…
External supply of oxygen to the atmospheres of the giant planets
Lellouch, E.; Encrenaz, T.; de Graauw, T. +3 more
The atmospheres of the giant planets are reducing, being mainly composed of hydrogen, helium and methane. But the rings and icy satellites that surround these planets, together with the flux of interplanetary dust, could act as important sources of oxygen, which would be delivered to the atmospheres mainly in the form of water ice or silicate dust…
A high deuterium abundance at redshift z = 0.7
Ferlet, R.; Vidal-Madjar, A.; Lemoine, M. +4 more
Of the light elements, the primordial abundance of deuterium relative to hydrogen, (D/H)p, provides the most sensitive diagnostic for the cosmological mass density parameter, ΩB. Recent high-redshift D/H measurements are highly discrepant, although this may reflect observational uncertainties,. The larger primordial D/H value…
Detection of ozone on Saturn's satellites RHEA and Dione
Johnson, R. E.; Cruikshank, D. P.; Pendleton, Y. J. +2 more
The satellites Rhea and Dione orbit within the magnetosphere of Saturn, where they are exposed to particle irradiation from trapped ions. A similar situation applies to the galilean moons Europa, Ganymede and Callisto, which reside within Jupiter's radiation belts. All of these satellites have surfaces rich in water ice. Laboratory studies of the …
Anomalously small magnetic field in the local interstellar cloud
Gloeckler, George; Geiss, Johannes; Fisk, L. A.
The solar wind carves out a cavity, known as the heliosphere, in the warm local interstellar cloud, which is itself embedded in a larger hot cloud. It is generally assumed that there is an overall pressure balance between these three regions. Thermal pressure and magnetic field pressure in the local interstellar cloud should therefore balance the …
The optical counterpart of the isolated neutron star RX J185635-3754
Walter, Frederick M.; Matthews, Lynn D.
The extreme densities of neutron stars make them an ideal system in which to investigate the equation of state of nuclear matter; accurate determinations of neutron star masses and radii are crucial for this. Current observations of neutron stars in binary systems yield masses that are generally consistent with theory. But measurements of radii ar…