Distant galaxies are moving away, but at what speed?

  • 1 Replies
  • 3098 Views

0 Members and 1 Guest are viewing this topic.

*

Offline RealEarthling

  • First timers
  • *
  • 6
    • View Profile
I hear a lot about the expanding universe and recent reports tell us that some galaxies are moving away even faster than before (meaning acceleration).  But I never hear anything about actual speed or, for that matter, Velocity (V).  I suppose there would be many different values for different galaxies, but I just wonder about order of magnitude (.2c, .5c, .7c??? - c! ?)   Larry

*

Offline PhysBang

  • Hero Member
  • *****
  • 592
    • View Profile
Distant galaxies are moving away, but at what speed?
« Reply #1 on: 19/04/2010 23:51:11 »
A really good review of the expansion is here: http://lanl.arxiv.org/abs/astro-ph/0310808

"Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe" Tamara M. Davis & Charles H. Lineweaver

That might provide more info than you want, though.

In general, the recession, v, of a distant galaxy from our position is  v = cz, where c is the speed of light and z is the measurement of the redshift of the galaxy. This approximation holds for redshifts of appreciably less than 0.5. At about redshift 1.5, a galaxy is, at present, moving away from us at the speed of light and more distant galaxies are moving away from us faster.