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Extensive and meticulous observations of the rotation curves of galaxies show that they are either flat or gently going up,
but rarely decreasing, at large galactocentric distances. Here we show that the gravitational potential which would lead to
such rotation curves arises naturally when the visible matter modelled as a collisionless Maxwellian gas is embedded in a
dark halo of collisionless particles with a much higher dispersion in velocities. 相似文献
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If the dwarf spheroidals are embedded in an extended cloud of dark matter then their density profiles can be reproduced by
assuming a Maxwellian distribution of velocities for the constituent stars. The observed luminosity profiles of dwarf spheroidals
imply densities for the dark matter in the range 10-26 to 10-25 g cm-3, and mass-to-luminosity ratios which are typically an order of magnitude greater than those of globular clusters. Neutrinos
of mass ∼ 10 eV and (v) ∼ 1000 km s-1 can provide this requisite density for the background. 相似文献
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Cowsik Ramanath Singh Jagdev Saxena A.K. Srinivasan R. Raveendran A.V. 《Solar physics》1999,188(1):89-98
Encouraged by the detection of high-frequency, low-amplitude continuum intensity oscillations in the solar corona during the total solar eclipse of 1995, we designed and fabricated a six-channel photometer incorporating low-noise Hamamatsu R647 photomultipliers. Fast photometry at five different locations in the solar corona was performed at Don Bosco Mission, Venezuela during the total solar eclipse of 26 February 1998. Three interference filters with passbands of about 150 Å and centered around 4700, 4900, and 5000 Å were used. The photometric data were recorded at a rate of 20 Hz in three channels and 50 Hz in the remaining three channels. The power spectrum analysis of one of the channels that recorded appreciable counts indicates the existence of intensity oscillations in the frequency range 0.01–0.2 Hz. A least-squares analysis yields 90.1, 25.2, and 6.9 s periods for the three prominent components which have amplitudes in the range 0.5–3.5% of the coronal brightness. These periods and their amplitudes are similar to those detected in the coronal intensity oscillations during the 1995 eclipse. 相似文献
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