A Look Back in Time...

[morningstar]

news.aol.com/story/_a/hubble-telescope-spies-ancient-galaxy/20080212171809990001

[elijah]

Can anyone explain gravitational lensing?

"The discovery [of this galaxy] was made possible by a natural magnifying glass — the galaxy cluster Abell 1689, which lies between us and the distant galaxy. Abell 1689's gravity is so strong it bends light that passes near it, acting like a giant zoom lens that magnifies what we see."

My confusion concerning gravitational lensing is that light is bent AWAY from Abell 1689 (thus magnifying the distant object) and not pulled INTO the galaxy as one would expect from the force of gravity.

Gravity usually compels and not repels and that is what confuses me.

Any thoughts?

[Frater G]

elijah said:

Can anyone explain gravitational lensing?

"The discovery [of this galaxy] was made possible by a natural magnifying glass — the galaxy cluster Abell 1689, which lies between us and the distant galaxy. Abell 1689's gravity is so strong it bends light that passes near it, acting like a giant zoom lens that magnifies what we see."

My confusion concerning gravitational lensing is that light is bent AWAY from Abell 1689 (thus magnifying the distant object) and not pulled INTO the galaxy as one would expect from the force of gravity.

Gravity usually compels and not repels and that is what confuses me.

Any thoughts?

Hmmm, I cannot see how gravity can repel anything. Wikipedia though has a good page on the theory of lensing.

en.wikipedia.org/wiki/Gravitational_lensing

[vajramukti]

elijah said:

Can anyone explain gravitational lensing?

"The discovery [of this galaxy] was made possible by a natural magnifying glass — the galaxy cluster Abell 1689, which lies between us and the distant galaxy. Abell 1689's gravity is so strong it bends light that passes near it, acting like a giant zoom lens that magnifies what we see."

My confusion concerning gravitational lensing is that light is bent AWAY from Abell 1689 (thus magnifying the distant object) and not pulled INTO the galaxy as one would expect from the force of gravity.

Gravity usually compels and not repels and that is what confuses me.

Any thoughts?

Abell is between us and the distant galaxy. Abell's gravity pulls the light from that galaxy towards Abell, and therefore towards us, making it look closer and larger from our perspective. It is like standing behind someone and peering through their glasses.

Does that help?

[elijah]

Does that help?

Not really but thank you. From what I understand of G. Lensing, light appears to be repelled by the gravitational mass of Abell and I want to know why that happens. Unless I have misunderstood the Wiki explanations.

[morningstar]

It is like standing behind someone and peering through their glasses.

This is a very good analogy - thanks, Vaj.

Here is a site which helped me grasp this a bit better:

In a system where lensing occurs there is a:
>source: where the light comes from, can be a quasar, the cosmic microwave background, a galaxy, etc.
>lens(es): which deflect(s) the light by an amount related to its quantity of mass/energy, can be anything with mass/energy
>observer: who sees a different amount of light than otherwise because the lens has bent spacetime and thus the travel paths of the light
>image or images: what the observer sees

The light is not only visible light, but more generally any radiation.
As a consequence of lensing, light rays that would have otherwise not reached the observer are bent from their paths and towards the observer. (Light can also be bent away from an observer but that is not the case of interest.) There are different regimes: strong lensing,weak lensing, and microlensing. The distinction between these regimes depends on the positions of the source, lens and observer, and the mass and shape of the lens (which controls how much light is deflected and where).

The above was quoted from:
astro.berkeley.edu/~jcohn/lens.html

I may be wrong ... but from what I can understand so far - as the light from this distant galaxy travels through space/time toward us - it passes through the Abell galaxy...as it does so, the Abell galaxy causes the path of the light to be deflected...so it would then act as a magnifying glass would...allowing us, perhaps, to see things we would not normally see.

On a different track - What amazes me so much about space/time ... we see things as they were - not as they are at present. Wild stuff. It is possible to look back in time...what we are able to observe of this distant galaxy today is what it looked like many billions of years ago. I wonder if there is someone on that distant galaxy looking toward us...wondering with the same awe...but then, no - they would not see our galaxy yet?...for we are relatively young in comparison...if our galaxy came into being long after this one - it will take the equivalent amount of time for our light to reach them...Man! There really were speed limits put in place, weren't there?
I need another coffee!

[Frater G]

elijah said:

Does that help?

Not really but thank you. From what I understand of G. Lensing, light appears to be repelled by the gravitational mass of Abell and I want to know why that happens. Unless I have misunderstood the Wiki explanations.

What Einstein theorized is that space is like fabric and the light will travel through this fabric like water through a curved pipe you could say. The gravitational fields around stars and black holes bend this fabric.

[vajramukti]

elijah said:

Does that help?

Not really but thank you. From what I understand of G. Lensing, light appears to be repelled by the gravitational mass of Abell and I want to know why that happens. Unless I have misunderstood the Wiki explanations.

That is not what I read. Light is bent by Abell's gravity, but it does not appear to say that it is repelled. It does say that the gravitational attraction in lensing is strongest at the center and weaker at the edges, which should be causing the center of the magnified object to appear closer.