APOD: Abell 370: Galaxy Cluster Lens... (2016 Aug 28)

[APOD Robot]

Abell 370: Galaxy Cluster Gravitational Lens

Explanation: What is that strange arc? While imaging the cluster of galaxies Abell 370, astronomers had noted an unusual arc to the right of many cluster galaxies. Although curious, one initial response was to avoid commenting on the arc because nothing like it had ever been noted before. In the mid-1980s, however, better images allowed astronomers to identify the arc as a prototype of a new kind of astrophysical phenomenon -- the gravitational lens effect of entire cluster of galaxies on background galaxies. Today, we know that this arc actually consists of two distorted images of a fairly normal galaxy that happened to lie far behind the huge cluster. Abell 370's gravity caused the background galaxies' light -- and others -- to spread out and come to the observer along multiple paths, not unlike a distant light appears through the stem of a wine glass. In mid-July of 2009, astronomers used the then just-upgraded Hubble Space Telescope to image Abell 370 and its gravitational lens images in unprecedented detail. Almost all of the yellow images featured here are galaxies in the Abell 370 cluster. An astute eye can pick up many strange arcs and distorted arclets, however, that are actually images of more distant galaxies. Studying Abell 370 and its images gives astronomers a unique window into the distribution of normal and dark matter in galaxy clusters and the universe.

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[tedzzz]

The wikipedia link in the last line reports inconisistent distances: para 1 of the link refers to distance 6 billion ly, vs observaton data 4.7775 billion ly.
The last para in the body of text reports that other galaxies lie at distances of 5 billion ly. The 6 billion ly appears incorrect.

[Merv]

It would almost appear that our deep space visuals of the universe have a mirrored appearance that would be duplication of various galaxies. My perspective may well be skewed and yet the subject of lensed viewing begs to question the position of all that I am able to view as being a one only or totally accurate appearance.

[Ann]

Click to view full size image

Redshift versus distance.
Source: http://homepages.wmich.edu/~korista/phy ... ppnts.html

Click to view full size image

The remarkable elongated okra-colored background galaxy at right is, of course, the most eye-catching object in today's APOD. The two distorted images link takes us to a page which claims that the redshift of this object is ~0.8. That means, or so I think, that the universe has become 80% larger through expansion since the light of that background galaxy was emitted. Also the distance to that background galaxy is ~10 billion light-years. Whatever.

As a color commentator, I am of course hugely interested in this object's color. We can see a very small and faint yellow center in the galaxy - it is most obvious in the center of the "swelling" near the bottom. (This may sound rude, but to me the elongated galaxy is slightly similar in shape to a sperm swimming downwards.)

Outside the faint yellow center is what looks like spiral arms. There are some bright blue knots in those spiral arms, which are undoubtedly bright clusters of young stars. But the overall color of the galaxy is the color of clay. Why is that?

Click to view full size image

NGC 157. Photo: Adam Block.

I can only guess. As old as it is, the lensed galaxy may nevertheless have had an interesting past. It may have undergone one or many intense bursts of star formation, which produced very many stars and a lot of dust. At the time this galaxy was lensed and "had its distorted photograph taken", the starburst was largely over, and only a few bright clusters were still forming. The stars that had formed in the intense starburst were now aging and no longer blue, but because there were so many of them their combined light was still bright. Also there might be quite a lot of dust left over from the original starburst and scattered all over the galaxy, reddening its overall light. And then, of course, the overall color of this galaxy is reddened by redshift-reddening.

In short, I'm thinking that the lensed galaxy might really look a bit like NGC 157 at left. Note the small yellow center, the bright intermediate-aged non-blue disk and arms, and the pink and blue sites of new and ongoing star formation.

Ann

[Guest]

Given that the probability of life is greater than zero (proven by life on earth), and that the probability of intelligent life is also greater than zero (assuming that we are intelligent life), then it follows that we are not alone.... Mind bending photo....

[Observer51]

Are the yellow galaxies gravitationally lensed as well?

[Ann]

Are the yellow galaxies gravitationally lensed as well?

The arc-shaped galaxies are lensed, whatever their color.

Ann

[heehaw]

Given that the probability of life is greater than zero (proven by life on earth), and that the probability of intelligent life is also greater than zero (assuming that we are intelligent life), then it follows that we are not alone.... Mind bending photo....

You can have lots of fun with probabilities! If the probability of intelligent life is not zero (and it is not) but that probability is smaller than the universe is vast (as it may be) then we ARE (likely) alone. On the other hand, if the universe is infinite (which we will probably never know) then there are infinitely many planets like Earth with creatures like us, including publishing APODS!

[ygmarchi]

I see you pretty much enjoy some lateral fun

[Chris Peterson]

The wikipedia link in the last line reports inconisistent distances: para 1 of the link refers to distance 6 billion ly, vs observaton data 4.7775 billion ly.
The last para in the body of text reports that other galaxies lie at distances of 5 billion ly. The 6 billion ly appears incorrect.

Astronomers generally don't consider cosmological distances in terms of units like light years, except when it's a convenient approximation to give a sense of scale. Redshift is the primary (and precise) measurement. Abell 370 has a redshift of 0.375, and that's the unit of distance that is most useful. You can plug that value into the standard equations to derive a distance (typically, the light travel time), but that equation contains constants (the omega values, the Hubble constant) that are not themselves very well constrained, so the value you choose for them will affect the final result. Bottom line: don't take cosmological distance values expressed as anything other than redshift too seriously.

[ta152h0]

whoever is in charge ( the chief engineer ) of this universe, sure is good at messing with our minds

[Observer51]

Are all of the galaxies in this image gravitationally lensed one way or another?

[Baldwin504]

It seems to me entirely possible with the recent news about Dragonfly44 that if there are as many dark matter galaxies as the math suggests, then many of these visible galaxies may simply be lensed duplicates. Is there any work being done to find out if this is correct?

[Chris Peterson]

Are the yellow galaxies gravitationally lensed as well?

If they look like galaxies, they are not lensed (or not visibly so- technically, everything you look at is lensed to some extent).

[Chris Peterson]

It seems to me entirely possible with the recent news about Dragonfly44 that if there are as many dark matter galaxies as the math suggests, then many of these visible galaxies may simply be lensed duplicates. Is there any work being done to find out if this is correct?

None of the things that look like galaxies- extended, generally oval blobs- are lensed. They are individual galaxies. The fine lines and arcs are all lensed galaxies. There are more lensed artifacts than there are background galaxies. It is possible spectroscopically to determine which artifacts are assigned to which background galaxies.

[Baldwin504]

Thanks

[starsurfer]

The gravitational arcs in this galaxy cluster have been resolved by amateurs, check out this image by CHART32.

[Observer51]

I wonder if there is a large-scale, combined Einstein Cross-Einstein Ring effect in this image of Abell 370.