# Field of Moving masses

Tags:
1. May 19, 2016

### Supantho Raxit

A moving charge that starts or stops generates a spherical wave-front of EM wave, can the same analogy be drawn for a moving mass?

Reference: Electricity & Magnetism by EM Purcell

2. May 19, 2016

### Staff: Mentor

It will emit gravitational waves, yes, mass is the "charge" of gravity. Usually that is completely negligible.

3. May 19, 2016

### Supantho Raxit

So, by drawing analogy with EM, I can easily find the eqn of field of a moving mass, the power radiated or other quantities ???
And, as this is highly negligible, is that the reason why it took so long to detect it?

4. May 19, 2016

### Staff: Mentor

It is a bit more complicated for gravity, but yes, in principle it is possible.
Right. You need really massive objects accelerating really fast to produce notable gravitational waves.

5. May 19, 2016

### pervect

Staff Emeritus
The analogy isn't quite perfect - gravitational radiation is given by a quadrupole formula, EM radiation by a dipole formula. This is related to the issue that you just can't have a moving mass stop for no reason, the conservation of momentum is built into the Einstein field equations, and a mass stopping with no cause is therefore not a solution of Einstein's field equations. So you need to reformulate your test problem in a way that conserves momentum in order to actually solve the equations and get out a number for gravitational radiation.

See for instance the wiki https://en.wikipedia.org/wiki/Gravitational_wave
I snipped some confusing parts of the wiki article that relate to higher order moments. A slightly better statement of what I snipped is is from http://www.tat.physik.uni-tuebingen.de/~kokkotas/Teaching/NS.BH.GW_files/GW_Physics.pdf