Space Warps Talk

Mass of Lenses

  • psaha by psaha scientist

    OK, this particular beauty is known: 66 on this list by anupreeta, but it's fun to estimate the lens mass using just the information on Spacewarps images.

    Taking the usual expressions for Einstein radius and stuff, and working through the arithmetic, gives a formula like:

    Mass in solar masses = (Area of image region, in pixels) x (Distance to lens, in parsecs)

    This is assuming the source is much further away than the lens. If the source is closer, the mass comes out a bit less. There's a numerical factor, but for this particular survey, the factor is close to one.

    The area of the image region here would be thousands of pixels. If the lens is a billion parsecs away, that would give a mass of several trillion solar masses. Now, the mass of the Local Group of the Milky Way and Andromeda is estimated around five trillion solar masses. So the lens here would be a big elliptical (perhaps the central galaxy in a cluster?) with a mass comparable to our Local Group.

    Posted