Teach Astronomy - Motion of Satellites скачать в хорошем качестве

Teach Astronomy - Motion of Satellites

http://www.teachastronomy.com/ An excellent way of measuring the total mass of either spiral or elliptical galaxies is to use the motion of dwarf satellite companions. Most elliptical galaxies and many spiral galaxies have a number of dwarf companions when studied with deep imaging. The technique depends on the fact that these dwarf companions are ten, twenty, or even a hundred times less massive than the primary galaxy. Astronomers measure the Doppler motions for as many companions as they can, and they use the range of Doppler motions as an estimate of the mass of the major galaxy. This technique leads to the inference that most of the mass of each of the types of galaxies, spirals and ellipticals, is in a dark matter halo. The motions of satellites is a good way to get the total mass of the galaxy because the satellites are found well beyond the halo at distances of up to one megaparsec.