Strange Galaxy Lensing

[SLD]

Abell 68 was imaged a few years ago by the Hubble. It shows a strange alien looking double image of a galaxy:



The one I the upper left. It looks like an angry alien robot. But the image doesn’t seem to make sense. I would’ve thought that a double image wouldn’t form on one side of the lens only. It seems like the central Galaxy Is pushing light away.

Or is this really a double image, or a merging Galaxy?

What all can these lensing events tell us about the distribution of matter in the foreground cluster? Can it show with more detail the distribution of dark matter vs. ordinary? And if so what exactly have we learned from such?

SLD

 

[Loren Pechtel]

The lensing might be being caused by something other than the nearby galaxy. An old neutron star in our own galaxy could cause lensing without being detectable by other means.

 

[Bomb#20]

NASA has a page about this photo here:

https://www.nasa.gov/mission_pages/hubble/science/abell68.html

There's a second image of the same background galaxy, below and to the left of the angry alien robot, about half way to the left edge.

 

[SLD]

NASA has a page about this photo here:

https://www.nasa.gov/mission_pages/hubble/science/abell68.html

There's a second image of the same background galaxy, below and to the left of the angry alien robot, about half way to the left edge.

I see it. That now makes sense. It’s a triple image. I wonder what all this says about the distribution of matter in the lensing cluster.

 

[Bomb#20]

I see it. That now makes sense. It’s a triple image. I wonder what all this says about the distribution of matter in the lensing cluster.

Well, just shooting my mouth off in an area where I have no expertise... I imagine each pixel gives you an equation, and the hypothetical mass density in each pixel-sized volume in the foreground cluster gives you a variable, and you need to solve for the variables using the equations. But the pixels form a 2-D image while the variables form a 3-D cluster, which means you have hundreds of times more variables than equations. So you can solve for the variables in a gazillion different ways -- the problem is massively underconstrained. The computer will hand you a lot of totally different solutions and say "All of these distributions would account for what you see.", and then you have to look at them all and decide which is more plausible than which. So I suspect all we're going to get is suggestive hints and free rein for astronomers' educated guesses.

 

[Shadowy Man]

Because the distances from the lensed galaxy to the cluster and from the cluster to us (the observer) are so large, compared to the size of the cluster itself, I am guessing that a two-dimensional dark matter distribution would suffice in solving for the lensing, so I’m not sure it’s as bad as you make it out to be.

Admittedly, this is not my area of expertise.