# Simple question needs answer

1. Apr 9, 2006

### ACLerok

Is there a way to find the electron concentration of an object (N/V; number of free electrons per unit volume) given only that it's mass density is 7.0 * 10^17 kg/m^3? Thanks.

2. Apr 9, 2006

### nrqed

The short answer is: no.

You need to know what it is made of!

3. Apr 9, 2006

### Astronuc

Staff Emeritus
That is extremely dense material - as in a neutron star.

One would have to know the nuclear reactions taking place in order to determine the equilibrium concentration for free electrons, which would ostensibly come from the decay of free neutrons.

Pulsars have free electrons - http://hyperphysics.phy-astr.gsu.edu/Hbase/astro/pulsar.html#c4

http://cassfos02.ucsd.edu/public/tutorial/SN.html [Broken] - search for "free electrons" on the page

http://www.astro.soton.ac.uk/~bexmgr/xrpulsar.html [Broken]

Last edited by a moderator: May 2, 2017
4. Apr 9, 2006

### nrqed

Good point.. I had not paid attention to the exponent of the density when I read the question. I thought it was ordinary matter. Thanks for pointing this out.

5. Apr 10, 2006

### ACLerok

Ohh, I forgot to mention that the object is indeed a neutron star. Would u just multiply that number above by the mass of a single neutron? I am stuck.. :/

6. Apr 11, 2006

### nrqed

Wait a minute!
Are you asking for the concentration of *neutrons* or of *electrons*?? If it is a question about neutrons, then it is extremely simple. If it is a question about electrons, then it is quite advanced and Astronuc gave some hints in that direction. It makes a huge difference...It goes from a high scholl level question to a physics undergrad (or higher) level question!

Patrick