Dark matter strikes again
Article Abstract:
Recent Rosat observations suggest the presence of dark matter in small groups of galaxies such as HG62 and HG92. Dark matter had been previously associated with individual galaxies and rich clusters. Both compact groups exhibit low metallicity and a four per cent baryon mass to dark mass ratio for HG92 and 13 percent for HG62. The problem with HG62 is that it has too few baryons to account for the dark matter but too numerous to be accomodated by the simplest cosmological model. This maybe caused by spreading out of gas by galactic winds or overestimation of gas density. There is evidence that cooling flow occurs for compact groups.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1993
User Contributions:
Comment about this article or add new information about this topic:
Gamma-ray bursts as collimated jets from neutron star/black hole mergers
Article Abstract:
Gamma-ray bursts in space may result from neutrino-antineutrino annihilation brought on when a black hole clashes with a stellar-mass neutron star. Astrophysicists have struggled to explain the approximately 150 gamma-ray bursts that have been discovered, but the new model accounts for how the bursts are able to overcome the optically thick stellar winds that accompany the bursts. The angular momentum conservation that would occur with neutrino annihilation would enable the bursts to escape into space.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1993
User Contributions:
Comment about this article or add new information about this topic:
Decaying neutrino theory
Article Abstract:
Analysis of X-rays emitted by dark matter in the A665 galaxy cluster supports Sciama's decaying neutrino theory, which holds that such dark matter X-ray data should be mostly baryonic. Hence the inability of A.F. Davidsen and colleagues to find an unidentified emission line at about 15 eV does not overturn the theory as they believed. The theory will stand until large amounts of nonbaryonic dark matter in clusters have been detected.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1992
User Contributions:
Comment about this article or add new information about this topic:
- Abstracts: Ice cores and mammoth extinction. Contrasting atmospheric and climate dynamics of the last-glacial and Holocene periods
- Abstracts: Temperatures in the Earth's core from melting-point measurements of iron at high static pressures. High-pressure polymorphs of olivine and the 660-km seismic discontinuity
- Abstracts: Liquid-crystalline phases as templates for the synthesis of mesoporous silica. Fragile-to-strong transition and polyamorphism in the energy landscape of liquid silica
- Abstracts: Badge size in collared flycatchers predicts outcome of male competition over territories. The effects of territory quality on age-dependent reproductive performance in the northern wheatear, Oenanthe oenanthe
- Abstracts: Temporal variation in responses to intraspecific brood parasitism in the moorhen. Factors affecting the rates of intraspecific nest parasitism among Anseriformes and Galliformes