<p>OK, guessing rather wildly in the absence of solid information....</p>

<p>The press-release page is <a href="http://ewass.kuoni-congress.info/press/2019/06/22/muse-reveals-a-glowing-ring-of-light-in-the-distant-universe/" rel="noreferrer">here</a>; that provides a bit more information
than the news article, and includes <em>two</em> images of (different regions of) the cluster and a hint that the cluster is named MACS0940.</p>

<p>I think the main image is a color composite from <em>HST</em> imaging. It shows a galaxy cluster (the yellow galaxies). Also visible is light from an Einstein ring, the gravitational lensing by the cluster of a (single) distant background galaxy. The thin, white, ringlike streaks within the pink arcs are the stellar light from this galaxy (probably UV light from massive, recently formed stars); the broad pink arcs themselves are (I'm guessing) the Lyman-alpha emission as seen by MUSE. (So the image is a composite of both HST data <em>and</em> MUSE data.) Thus it is plausible to say that the Einstein ring is made up of stellar light from the background galaxy and (in pink) emission from gas in and around that same galaxy; the assumption is that said gas is mostly in a halo around the galaxy.</p>

<p>The second "magnified" galaxy referred to in the news article is probably in a different part of the cluster, and doesn't form a nice Einstein ring; it is presumably the four pink blobs in the second image on the press-release page.</p>

<p><a href="http://www.stsci.edu/hst/phase2-public/15696.pro" rel="noreferrer">This</a> is the abstract for an <em>HST</em> proposal on which Claeyssens was a co-I; the data were taken on May 1, 2019, so it's plausible the image is from those observations:</p>

<blockquote>
  <p>Recent deep integral-field spectroscopy observations using VLT/MUSE
  revealed two     high-redshift (z>4) lensed arcs in the galaxy cluster
  MACS0940. Notably, both lensed galaxies show highly extended
  Lyman-alpha emission (> 5 arcsec)... one of these galaxies forms an
  almost complete Einstein ring, with the Lyman-alpha arc reaching an
  unrivaled extent of 30 arcsec.</p>
</blockquote>

CC BY-SA 4.0
2019-06-25T10:05:12.943Z
Thank you for the celestial sleuthing! I hadn't thought about a composite image but that can explain a lot. I see you've [mentioned MUSE](https://astronomy.stackexchange.com/questions/26989/how-did-vlts-adaptive-optics-obtain-this-resolution-for-neptune-is-it-really-w/26993#comment49768_26993) before as well.
uhoh
CC BY-SA 4.0
2019-06-25T09:48:47.123Z
2019-06-25T09:48:47.123Z
Peter Erwin
<p>I'm having a hard time understanding this image in the CNN News item <a href="https://edition.cnn.com/2019/06/24/world/muse-glowing-ring-of-light-scn-trnd/index.html" rel="nofollow noreferrer">This glowing ring of light is from a distant galaxy</a>.</p>
<p>The caption (<a href="https://www.abc17news.com/news/national-world/this-glowing-ring-of-light-is-from-a-distant-galaxy/1088915478" rel="nofollow noreferrer">from this version</a> of the article) says:</p>
<blockquote>
<p>This  image shows observations taken with the NASA/ ESA Hubble Space Telescope of two magnified galaxies behind massive galaxy clusters: the pink glowing haloes reveal the gas surrounding the distant galaxies and its structure. The gravitational lensing effect from the clusters multiplies the images of the galaxies, producing up to 4 images of the same source.</p>
</blockquote>
<p>Trying to parse the caption, I think that the two objects in the center are magnified images of the galaxies in the background, and so should be related to the source of the light in the Einstein ring. But they are yellow and the ring is pink.</p>
<p><strong>Question:</strong> So the Einstein ring is picking up light not from the background galaxies, but from a halo of gas around them? Is there a better source to read about this image and everything that's going on here?</p>
<p>The image contains the following label at the top right corner:</p>
<p><img src="https://i.sstatic.net/F5sjC.png" alt="gravitationally lensed galaxies and Einstein ring - label" /></p>
<p>click for full size:</p>
<p><img src="https://i.sstatic.net/exZqT.jpg" alt="gravitationally lensed galaxies and Einstein ring" /></p>
<hr />
<p>The article then says:</p>
<blockquote>
<p>The MUSE instrument on the European Southern Observatory's Very Large Telescope has identified halos around distant galaxies. Previously, images of these glowing rings lacked detail, but astronomers were able to use a gravitational lensing effect of galaxy clusters to see detail and structure.</p>
<p>Gravitational lensing occurs as an effect of Albert Einstein's theory of general relativity: mass bends light. So the gravitational fields of galaxy clusters bend light, acting like a magnifier of the galaxies behind them.</p>
<p>The best observations of the halos by MUSE were released Monday, presented by Adélaïde Claeyssens during the annual meeting of the European Astronomical Society in Lyon, France. Claeyssens is a Ph.D. student at the Centre de Recherche Astrophysique de Lyon.</p>
</blockquote>
<p>Which further confuses me because the caption mentions Hubble but the article mentions data from MUSE at the VLT. I wonder if the image is a file photo and only peripherally related to the content of the news article?</p>

CC BY-SA 4.0
2019-06-25T05:44:00.847Z
I think the author has confused "Halo of dark matter around the foreground galaxy" (which is largely the source of the mass which produces the ring) with "Halo of gas around the galaxy.  The are confused because "Halo" sounds like a ring, and, hey, the picture has a ring.... so that must be the halo, right??
James K
CC BY-SA 4.0
2019-06-25T09:11:54.500Z
I'm going to guess that the main image is from HST, and that the pink ring is perhaps from MUSE emission-line gas measurements of the distant background (lensed) galaxy. (The two objects in the center are part of the cluster.)
Peter Erwin
CC BY-SA 4.0
2019-06-25T09:12:51.717Z
This appears to very much in-progress, unpublished work, and is only being presented at the EWASS meeting *today*, so I suspect there isn't much else out there.
Peter Erwin
CC BY-SA 4.0
2019-06-25T09:39:06.430Z
Beside colours and their origin, the yellow objects at the center must be those, or being part of those, acting as gravitational lense, being the source of the pink ring behind them.
Alchimista
<galaxy-cluster><gravitational-lensing>
Why is this Einstein ring pink?
uhoh
# Why is this Einstein ring pink?

(Asked by: username_0 on 2019-06-25)

I'm having a hard time understanding this image in the CNN News item [This glowing ring of light is from a distant galaxy](https://edition.cnn.com/2019/06/24/world/muse-glowing-ring-of-light-scn-trnd/index.html).

The caption ([from this version](https://www.abc17news.com/news/national-world/this-glowing-ring-of-light-is-from-a-distant-galaxy/1088915478) of the article) says:

> This image shows observations taken with the NASA/ ESA Hubble Space Telescope of two magnified galaxies behind massive galaxy clusters: the pink glowing haloes reveal the gas surrounding the distant galaxies and its structure. The gravitational lensing effect from the clusters multiplies the images of the galaxies, producing up to 4 images of the same source.

Trying to parse the caption, I think that the two objects in the center are magnified images of the galaxies in the background, and so should be related to the source of the light in the Einstein ring. But they are yellow and the ring is pink.

**Question:** So the Einstein ring is picking up light not from the background galaxies, but from a halo of gas around them? Is there a better source to read about this image and everything that's going on here?

The image contains the following label at the top right corner:

![gravitationally lensed galaxies and Einstein ring - label](https://i.sstatic.net/F5sjC.png)

click for full size:

![gravitationally lensed galaxies and Einstein ring](https://i.sstatic.net/exZqT.jpg)

---

The article then says:

> The MUSE instrument on the European Southern Observatory's Very Large Telescope has identified halos around distant galaxies. Previously, images of these glowing rings lacked detail, but astronomers were able to use a gravitational lensing effect of galaxy clusters to see detail and structure.
>
> Gravitational lensing occurs as an effect of Albert Einstein's theory of general relativity: mass bends light. So the gravitational fields of galaxy clusters bend light, acting like a magnifier of the galaxies behind them.
>
> The best observations of the halos by MUSE were released Monday, presented by Adélaïde Claeyssens during the annual meeting of the European Astronomical Society in Lyon, France. Claeyssens is a Ph.D. student at the Centre de Recherche Astrophysique de Lyon.

Which further confuses me because the caption mentions Hubble but the article mentions data from MUSE at the VLT. I wonder if the image is a file photo and only peripherally related to the content of the news article?

**Tags:** galaxy-cluster, gravitational-lensing
> **Comments:**
> **username_1**: I think the author has confused "Halo of dark matter around the foreground galaxy" (which is largely the source of the mass which produces the ring) with "Halo of gas around the galaxy.  The are confused because "Halo" sounds like a ring, and, hey, the picture has a ring.... so that must be the halo, right??  
> **username_2**: I'm going to guess that the main image is from HST, and that the pink ring is perhaps from MUSE emission-line gas measurements of the distant background (lensed) galaxy. (The two objects in the center are part of the cluster.)  
> **username_2**: This appears to very much in-progress, unpublished work, and is only being presented at the EWASS meeting *today*, so I suspect there isn't much else out there.  
> **username_3**: Beside colours and their origin, the yellow objects at the center must be those, or being part of those, acting as gravitational lense, being the source of the pink ring behind them.  

---

## 1 answers

### Answer by username_2 on 2019-06-25. Score: 6 | Accepted answer

OK, guessing rather wildly in the absence of solid information....

The press-release page is [here](http://ewass.kuoni-congress.info/press/2019/06/22/muse-reveals-a-glowing-ring-of-light-in-the-distant-universe/); that provides a bit more information
than the news article, and includes *two* images of (different regions of) the cluster and a hint that the cluster is named MACS0940.

I think the main image is a color composite from *HST* imaging. It shows a galaxy cluster (the yellow galaxies). Also visible is light from an Einstein ring, the gravitational lensing by the cluster of a (single) distant background galaxy. The thin, white, ringlike streaks within the pink arcs are the stellar light from this galaxy (probably UV light from massive, recently formed stars); the broad pink arcs themselves are (I'm guessing) the Lyman-alpha emission as seen by MUSE. (So the image is a composite of both HST data *and* MUSE data.) Thus it is plausible to say that the Einstein ring is made up of stellar light from the background galaxy and (in pink) emission from gas in and around that same galaxy; the assumption is that said gas is mostly in a halo around the galaxy.

The second "magnified" galaxy referred to in the news article is probably in a different part of the cluster, and doesn't form a nice Einstein ring; it is presumably the four pink blobs in the second image on the press-release page.

[This](http://www.stsci.edu/hst/phase2-public/15696.pro) is the abstract for an *HST* proposal on which Claeyssens was a co-I; the data were taken on May 1, 2019, so it's plausible the image is from those observations:

> Recent deep integral-field spectroscopy observations using VLT/MUSE
> revealed two high-redshift (z>4) lensed arcs in the galaxy cluster
> MACS0940. Notably, both lensed galaxies show highly extended
> Lyman-alpha emission (> 5 arcsec)... one of these galaxies forms an
> almost complete Einstein ring, with the Lyman-alpha arc reaching an
> unrivaled extent of 30 arcsec.

> **Comments:**
> **username_0**: Thank you for the celestial sleuthing! I hadn't thought about a composite image but that can explain a lot. I see you've [mentioned MUSE](https://astronomy.stackexchange.com/questions/26989/how-did-vlts-adaptive-optics-obtain-this-resolution-for-neptune-is-it-really-w/26993#comment49768_26993) before as well.  

---

