# Does the milky way have relativistic mass against galaxies which are moving away from it at high speeds?

According to the article cited behind, and to a post here in Astronomy SE , there are galaxies moving away from Milky Way faster than light, even at speeds of 2.3c . According to this article Can two galaxies move away from each other faster than light

The two galaxies we've been discussing are not travelling through space, it is the space between them that is expanding. Or put in another way, they are stationary and all the space around them is being stretched out. This is why it doesn't violate the theory of relativity, because it is not motion in the traditional sense.

So does this motion between galaxies "in not a traditional sense" count at all to calculate relativistic mass?

• "Relativistic mass" is an outdated concept. The momentum increases non-linearly with velocity, but not the gravitational attraction. – Asher Jun 28 '17 at 19:09
• If by relativistic mass, you're referring to $\gamma m$, where $\gamma$ is the Lorentz Factor, and $m$ is the "rest mass" of the body, then no. – zephyr Jun 28 '17 at 19:46
• @RobJeffries is that comment for me or for Asher? – Pablo Jun 28 '17 at 21:39
• Crossposted to physics.stackexchange.com/q/342031/2451 – Qmechanic Jun 29 '17 at 11:45