To examine what kinds of stars contribute to the overall density distribution in the solar neighbourhood, various statistical sampling arguments can be applied to catalogs and lists of stars. The result of such a procedure is summarized in the table, which lists some of the kinds of objects and gives the calculated mean density over an appropriate volume centred on the Sun. For rare objects such as globular clusters, the volume of the sample must of course be rather large compared with that required to calculate the density for more common stars.
| Space densities of stars | |
| object | density (solar mass per cubic light-year) |
| O, B stars | 0.00003 |
| A, F stars | 0.0001 |
| dG, dK stars | 0.0004 |
| dM stars | 0.0008 |
| gG, gK stars | 0.00003 |
| gM stars | 0.0000003 |
| dark companions | 0.00014 |
| white dwarfs | 0.0002 |
| long-period variables | 0.00000003 |
| RR Lyrae stars | 0.0000000003 |
| Cepheids | 0.00000003 |
| planetary nebulae | 0.00000000015 |
| open clusters | 0.0000011 |
| globular clusters | 0.00000003 |
The most common stars and those that contribute the most to the local stellar mass density are the dwarf M (dM) stars, which provide a total of 0.0008 solar masses per cubic light-year. It is interesting to note that RR Lyrae variables and planetary nebulae—though many are known and thoroughly studied—contribute almost imperceptibly to the local star density. At the same time, white dwarf stars, which are difficult to observe and of which very few are known, are among the more significant contributors.
Milky-Way-Galaxy-as-seen-from-EarthMilky Way Galaxy as seen from Earth[Credits : © Dirk Hoppe]
Bright-nebulosity-in-the-Pleiades-distance-490-light-yearsBright nebulosity in the Pleiades (M45, NGC 1432), distance 490 light-years.[Credits : Hale Observatories ©1961]
Centre-of-the-Orion-Nebula-Astronomers-have-identified-some-700Centre of the Orion Nebula (M42).[Credits : Photo AURA/STScI/NASA/JPL (NASA photo # STScI-PRC95-45a)]
Composite-picture-of-the-Cats-Eye-Nebula-combining-three-imagesComposite picture of the Cat’s Eye Nebula (NGC 6543), combining three images taken by the Hubble …[Credits : Photo AURA/STScI/NASA/JPL (NASA photo # STScI-PRC95-01a)]
The-Crab-Nebula-which-was-formed-by-a-supernova-explosionThe Crab Nebula, which was formed by a supernova explosion recorded in 1054. This image was made by …[Credits : NASA]
The-Eagle-NebulaThe Eagle Nebula. Stars are forming in this column of cold dust and gas, which is 9.5 light-years …[Credits : NASA, ESA, and The Hubble Heritage Team (STScI/AURA)]
Horsehead-NebulaHorsehead Nebula[Credits : © Anglo-Australian Observatory]
Globular-cluster-NGC-1850-in-the-Large-Magellanic-CloudGlobular cluster NGC 1850 in the Large Magellanic Cloud.[Credits : Photo AURA/STScI/NASA/JPL (NASA photo # STScI-PRC94-40)]
Our solar system is just a miniscule part of a much larger system called the Milky Way Galaxy.[Credits : Acquired from Vast Video]
The universe is made up of many stars, solar systems, and galaxies.[Credits : Acquired from Vast Video]
Using their telescope, the brother and sister team of William and Caroline Herschel discovered the …[Credits : Acquired from Vast Video]
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