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spaceSpace and PhysicsspaceAstronomy

JWST and Hubble's Combined Power Reveals Secrets And Surprises Of A Pair Of Galaxies

There is more than meets the eye in galaxy pair VV 191 about 715 million light-years from us.

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Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockOct 6 2022, 16:06 UTC
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The background of this JWST and Hubble composite image of galaxy pair VV 191 is black. Two large, very bright galaxies dominate the center of the image. The elliptical galaxy at left is extremely bright at its circular core, with dimmer white light extending to its transparent circular edges. At right is a bright spiral galaxy. It also has a bright white core, but has red and light purple spiral arms that start at the center and turn clockwise going outward. They end in faint red and appear to overlap the elliptical galaxy at left. Throughout the scene are a range of distant galaxies, the majority of which are very tiny and red, appearing as splotches.
Galaxy pair VV191. Image Credit: SCIENCE: NASA, ESA, CSA, Rogier Windhorst (ASU), William Keel (University of Alabama), Stuart Wyithe (University of Melbourne), JWST PEARLS Team IMAGE PROCESSING: Alyssa Pagan (STScI)

By combining data from the two titans of space telescopes, Hubble and JWST, astronomers have created an incredible image of two galaxies over 700 million light-years away that reveals secrets we wouldn't have seen by using just one.   

If you see a pair of galaxies in space there’s a good chance they’re interacting, but this is not the case for galaxy pair VV191. From our line of sight, the galaxies may look like they overlap, and in this case, they are also relatively close space-wise, but they have not started the gravitational dance that leads to merging yet.

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To truly appreciate their unambiguous separation, astronomers employed the two best space telescopes we have: Hubble, which sees in visible light, and JWST, which sees in infrared. While we can see the galaxy pair clearly with Hubble, their combined power allows scientists to see the overlapping regions of the galaxies in exquisite detail. 

The temperature of dust in interstellar space is very low so it can only be seen in infrared, which is where the power of JWST comes in. By looking at the interstellar dust, the images reveal no hallmark of mergers. The spiral galaxy is simply in front of the elliptical galaxy. Thanks to the elliptical backlighting of the spiral, the dust structures at the edge of the galaxy are revealed.

“VV 191 is the latest addition to a small number of galaxies that helps researchers like us directly compare the properties of galactic dust. This target was selected from nearly 2,000 superimposed galaxy pairs identified by Galaxy Zoo citizen science volunteers,” JWST scientist Thaddeus Cesari wrote in a blog post.

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“Understanding where dust is present in galaxies is important, because dust changes the brightness and colors that appear in images of the galaxies. Dust grains are partially responsible for the formation of new stars and planets, so we are always seeking to identify their presence for further studies.”

The background of this JWST and Hubble composite image of galaxy pair VV 191 is black. Two large, very bright galaxies dominate the center of the image. At right is a bright spiral galaxy. It has a bright white core and red and light purple arms that turn clockwise. The elliptical galaxy at left is extremely bright at its circular core, with dimmer white light extending to its transparent circular edges. An inset box that shows a close-up view of the center of the elliptical galaxy is at the bottom left corner of the image. The box highlights a distant, gravitationally lensed (magnified and warped) galaxy that appears as a stretched red arc around 10 o’clock and again as a tiny red dot at 4 o’clock at the core of the elliptical galaxy. This distant galaxy is so faint it was only identified with JWST
The lensed galaxy can be seen near the center of the elliptical galaxy in the white box highlight.


But that's not all. If you look near the core of the elliptical galaxy you will see the red distorted object at about 10 o’clock from the center. That is a much further galaxy, whose light traveled for almost 12 billion years before reaching us. It had to pass through the elliptical galaxy whose mass is warping space-time, creating a gravitational lens.

The lens has magnified the light of this distant galaxy, not enough to be spotted by Hubble but clearly visible by the sharper infrared eye of JWST. Preliminary work suggests the presence of a second lensed galaxy though experiencing just a minor distortion, something known as weak gravitational lensing.

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The preliminary study is available to read on ArXiv.org.  


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