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Direct detection of a microlens in the Milky Way
Alcock, C.; Allsman, R. A.; Alves, D. R. +22 more
The nature of dark matter remains mysterious, with luminous material accounting for at most ~25 per cent of the baryons in the Universe. We accordingly undertook a survey looking for the microlensing of stars in the Large Magellanic Cloud (LMC) to determine the fraction of Galactic dark matter contained in massive compact halo objects (MACHOs). Th…
An auroral flare at Jupiter
Desai, S.; McComas, D. J.; Young, D. T. +8 more
Jupiter's aurora is the most powerful in the Solar System. It is powered largely by energy extracted from planetary rotation, although there seems also to be a contribution from the solar wind. This contrasts with Earth's aurora, which is generated through the interaction of the solar wind with the magnetosphere. The major features of Jupiter's au…
Discovery of X-rays from the protostellar outflow object HH2
Maeda, Yoshitomo; Bally, John; Feigelson, Eric D. +3 more
Herbig-Haro (HH) objects have been known for 50 years to be luminous condensations of gas in star-forming regions, but their underlying physical nature is still being elucidated. Previously suggested models encompass newborn stars, stellar winds clashing with nebular material, dense pockets of interstellar gas excited by shocks from outflows, and …
Temporal evolution of the electric field accelerating electrons away from the auroral ionosphere
Balogh, A.; André, M.; Buchert, S. +10 more
The bright night-time aurorae that are visible to the unaided eye are caused by electrons accelerated towards Earth by an upward-pointing electric field. On adjacent geomagnetic field lines the reverse process occurs: a downward-pointing electric field accelerates electrons away from Earth. Such magnetic-field-aligned electric fields in the collis…
Substantial reservoirs of molecular hydrogen in the debris disks around young stars
Thi, W. F.; Natta, A.; van Dishoeck, E. F. +7 more
Circumstellar accretion disks transfer matter from molecular clouds to young stars and to the sites of planet formation. The disks observed around pre-main-sequence stars have properties consistent with those expected for the pre-solar nebula from which our own Solar System formed 4.5Gyr ago. But the `debris' disks that encircle more than 15% of n…
Gravitational microlensing by low-mass objects in the globular cluster M22
Casertano, Stefano; Livio, Mario; Albrow, Michael D. +4 more
Gravitational microlensing offers a means of determining directly the masses of objects ranging from planets to stars, provided that the distances and motions of the lenses and sources can be determined. A globular cluster observed against the dense stellar field of the Galactic bulge presents ideal conditions for such observations because the pro…
Space physics: Rhythms of the auroral dance
Newell, Patrick T.
Earlier this year, the four satellites of the Cluster mission passed through part of the electric circuit that causes aurorae. Their observations support the view that intense aurorae form in regions largely devoid of electrons.