Published online by Cambridge University Press: 19 July 2016
The observational evidence for unseen matter is briefly reviewed for objects ranging from small to very large scales. The existence of large mass discrepancies is clearly recognized in individual spiral galaxies and in rich clusters of galaxies. For other systems - dwarfs, ellipticals, binaries and groups - the results are more uncertain and still rather controversial. The data on spirals indicate values of the cosmological density parameter Ω around 0.02, those on clusters Ω ≃ 0.2. The spatial distribution of this dark matter is still largely unknown: while on the galaxy scale it must be located mainly in the outer parts of the stellar system, in clusters it is unclear whether it follows the distribution of the visible galaxies or not.
To send this article to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Dropbox account. Find out more about saving content to Dropbox.
To save this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Google Drive account. Find out more about saving content to Google Drive.