Two Halves that don't make a whole

[LaurieAG]

I came across the two articles below and wonder if anybody knows of any developments with regards to revised galaxy rotation curves and/or the total amount of dark matter?

'Lost in Space: Half of All Stars Are Rogues Between Galaxies' http://www.space.com/27682-rogue-stars-between-galaxies.html

As many as half of all stars in the universe lie in the vast gulfs of space between galaxies, an unexpected discovery made in a new study using NASA rockets. These stars could help solve mysteries regarding missing light and particles that theory had suggested should exist, scientists say.

'Milky Way has half the amount of dark matter as previously thought, new measurements reveal' http://www.sciencedaily.com/releases/2014/10/141009091600.htm

A new measurement of dark matter in the Milky Way has revealed there is half as much of the mysterious substance as previously thought. Australian astronomers used a method developed almost 100 years ago to discover that the weight of dark matter in our own galaxy is 800,000,000,000 times the mass of the Sun.

[Janus]

The only galaxy rotation curve to be revised would be that of the Milky way due to more accurate measurements of its halo stars, this has no effect on the measured rotation curves of other galaxies. (measuring our own rotation curve is more difficult since being inside our galaxy we can't see it in it's entirety.)

 

So we are really talking about 2 separate issues, the DM of our own galaxy and the DM of the universe as a whole. Even the discovery of as much as 1/2 of stars being between galaxies would only reduce the required DM by 1/4. Look at it this way, matter in the universe is estimated at 1/5 baryonic and 4/5 DM, so if the baryonic matter were found to make up twice its estimated fraction, then the ratio would go to 2/5 and 3/5. The DM portion goes from 4/5 to 3/5, which is just 1/4 less than its original estimate.( I bring this up because I've heard some people claim that this discovery of additional stars cuts the required DM by half, which is just not the case.)

[pantheory]

 

I came across the two articles below and wonder if anybody knows of any developments with regards to revised galaxy rotation curves and/or the total amount of dark matter?

'Lost in Space: Half of All Stars Are Rogues Between Galaxies' http://www.space.com/27682-rogue-stars-between-galaxies.html

'Milky Way has half the amount of dark matter as previously thought, new measurements reveal' http://www.sciencedaily.com/releases/2014/10/141009091600.htm

 

 

The dark matter hypothesis is based upon rotation curves of galaxies. This latest observation claims that stellar speeds in our outer galaxy are somewhat less than previously calculated based upon observations. If such new calculations and observations are more correct then there would be less hypothetical dark matter needed to explain the Milky Way's rotation curve.

 

There are other explanations than dark matter to explain rotation curves of galaxies, rotation rates of galaxies in a cluster, and the observed extent of gravitational lensing, but only a few of these alternative hypothesis/ explanations are generally known; most of them remain unknown. The point is that dark matter is still an unproven hypothesis developed to explain what are believed to be non-visible gravity influences that may or may not be real.

Edited December 20, 2014 by pantheory

[LaurieAG]

Thanks Janus and pantheory,

 

It will be interesting to see what the new calculations say as I was told on another forum that there would be no change..