User Tools

    To create and edit articles, please register and log-in

Main Menu : categories & index etc.

Main menu
Click categories to expand


A-Z listingplugin-autotooltip__plain plugin-autotooltip_bigA-Z listing

This is an alphabetical index of all content pages.


Other categories

Utilities

Contact
Register
Sandbox

Also see

Importance Ratings
News
Legal
Donate/Sponsor
Curator's rationale
AI Policy



Twitter feed 𝕏



Feeds + s.e.o. etc.
rss / xml feed
sitemap file
A-Z listing (archived)


Indexed under : Physics / Cosmology

Wikenigma - an Encyclopedia of Unknowns Wikenigma - an Encyclopedia of the Unknown

Galaxy mass anomalies

The gravitational pull of the combined masses of all the component stars and planets in a spiral galaxy must fall-off away from the centre, simply because there are less of them than in the tightly packed centre. So, before the 1970s, it had been assumed that stars which were further away from the centre of the galaxy would be rotating (around the central axis of the galaxy) at much slower speeds than those towards the centre.

But, in the 1970s, astronomers Vera Rubin and Albert Bosma published observational data which showed that the rotation speed of stars in (many) spiral galaxies appears to be roughly constant - from the centre to the outermost stars, and well beyond their optical discs. See :Galaxy Rotation Problemplugin-autotooltip__plain plugin-autotooltip_bigGalaxy Rotation Problem

"The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre. It is typically rendered graphically as a plot, a…

Those new observations, that the rotation speed was constant, led to the idea of Dark Matterplugin-autotooltip__plain plugin-autotooltip_bigDark Matter

"The nature of the dominant component of galaxies and clusters remains unknown.“

Source : Measuring the dark matter equation of state (Mon. Not. R. Astron. Soc. 415, L74–L77)"

In the 1930s, astronomical observations of galaxy rotations showed that the ou…
as a way of explaining the anomaly. By suggesting that 'missing mass' provided by the Dark Matter was apparently holding the galaxies together

With regard to our local galaxy - The Milky Way - new (2023) experimental data from the European Space Agency’s Gaia satellite appears to show that the outer-most stars are indeed revolving more slowly around the centre. Based on this, new calculations infer that the combined mass of the Milky Way is about four to five times less than had been suggested by several other earlier assessments. And so any 'Dark Matter' content would therefore also be considerably less than seems to be present in other galaxies.

There is currently no explanation for the observations.

Various possibilities have been suggested - including :

  • The Milky Way may in some way differ structurally from other spiral galaxies
  • For some reason there's only about half as much dark matter as in other similar galaxies
  • There are problems with the latest measurements
  • There are problems with previous measurements
  • Over cosmological times and distances gravity might not be constant

See : Detection of the Keplerian decline in the Milky Way rotation curve Astronomy & Astrophysics manuscript no. AA:2023:47513 September 21, 2023


    Please share this page to help promote Wikenigma !

Dear reader : Do you have any suggestions for the site's content?

Ideas for new topics, and suggested additions / corrections for older ones, are always welcome.

If you have skills or interests in a particular field, and have suggestions for Wikenigma, get in touch !


Or, if you'd like to become a regular contributor . . . request a login password. Registered users can edit the entire content of the site, and also create new pages.

( The 'Notes for contributors' section in the main menu has further information and guidelines etc.)

Automatic Translation

You are currently viewing an auto-translated version of Wikenigma

Please be aware that no automatic translation engines are 100% accurate, and so the auto-translated content will very probably feature errors and omissions.

Nevertheless, Wikenigma hopes that the translated content will help to attract a wider global audience.

Show another (random) article

Further resources :

DOKUWIKI IMPLEMENTATION DESIGN BY UNIV.ORG.UK DECEMBER 2023