APOD: A Molten Galaxy Einstein Ring (2022 Jul 05)

[APOD Robot]

A Molten Galaxy Einstein Ring

Explanation: It is difficult to hide a galaxy behind a cluster of galaxies. The closer cluster's gravity will act like a huge lens, pulling images of the distant galaxy around the sides and greatly distorting them. This is just the case observed in the featured image recently re-processed image from the Hubble Space Telescope. The cluster GAL-CLUS-022058c is composed of many galaxies and is lensing the image of a yellow-red background galaxy into arcs seen around the image center. Dubbed a molten Einstein ring for its unusual shape, four images of the same background galaxy have been identified. Typically, a foreground galaxy cluster can only create such smooth arcs if most of its mass is smoothly distributed -- and therefore not concentrated in the cluster galaxies visible. Analyzing the positions of these gravitational arcs gives astronomers a method to estimate the dark matter distribution in galaxy clusters, as well as infer when the stars in these early galaxies began to form.

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[orin stepanek]

Although the galaxy isn't really molten; it sure looks like it is! I wish
we could put the photo together to see what the galaxy really looks
like!

This kitty really gets around lately!

[howard.freeland]

We are in-line with the distant lensed galaxy and the gravitational lens itself. I'd like to presume that there really are astronomers on that distant galaxy gazing at the lensed Milky Way. I wonder what they would be seeing right now, whatever "right now" means in this relativistic universe?

[Chris Peterson]

We are in-line with the distant lensed galaxy and the gravitational lens itself. I'd like to presume that there really are astronomers on that distant galaxy gazing at the lensed Milky Way. I wonder what they would be seeing right now, whatever "right now" means in this relativistic universe?

This is an unusual system. The source is at z=1.48 (9.3 Gyr) and the lens is at z=0.36 (4 Gyr), meaning that the lens is approximately centered between us and the source. In most cases where we observe Einstein rings, the lens is much closer to us than the source, meaning that anybody at the source would likely not see our galaxy lensed. This is a rare case where they might.

[johnnydeep]

We are in-line with the distant lensed galaxy and the gravitational lens itself. I'd like to presume that there really are astronomers on that distant galaxy gazing at the lensed Milky Way. I wonder what they would be seeing right now, whatever "right now" means in this relativistic universe?

This is an unusual system. The source is at z=1.48 (9.3 Gyr) and the lens is at z=0.36 (4 Gyr), meaning that the lens is approximately centered between us and the source. In most cases where we observe Einstein rings, the lens is much closer to us than the source, meaning that anybody at the source would likely not see our galaxy lensed. This is a rare case where they might.

Cool!

[johnnydeep]

This is the most impressive and convincing picture of gravitational lensing that I've seen so far. I presume an unlensed image of the subject galaxy is not visible here. For the curious, as I was, here's a pic from the linked-to paper about the four separate images:

[beryllium732]

We are in-line with the distant lensed galaxy and the gravitational lens itself. I'd like to presume that there really are astronomers on that distant galaxy gazing at the lensed Milky Way. I wonder what they would be seeing right now, whatever "right now" means in this relativistic universe?

This is an unusual system. The source is at z=1.48 (9.3 Gyr) and the lens is at z=0.36 (4 Gyr), meaning that the lens is approximately centered between us and the source. In most cases where we observe Einstein rings, the lens is much closer to us than the source, meaning that anybody at the source would likely not see our galaxy lensed. This is a rare case where they might.

How do they know that the lensed galaxy is 9.3 Gyr away? How is it possible to measure that?

It's reddish orange color is because of the redshift? I see streams of blue bands which i guess is hot blue stars? But I guess that the lensed galaxy would be much more blue looking if it were much closer?

[Chris Peterson]

We are in-line with the distant lensed galaxy and the gravitational lens itself. I'd like to presume that there really are astronomers on that distant galaxy gazing at the lensed Milky Way. I wonder what they would be seeing right now, whatever "right now" means in this relativistic universe?

This is an unusual system. The source is at z=1.48 (9.3 Gyr) and the lens is at z=0.36 (4 Gyr), meaning that the lens is approximately centered between us and the source. In most cases where we observe Einstein rings, the lens is much closer to us than the source, meaning that anybody at the source would likely not see our galaxy lensed. This is a rare case where they might.

How do they know that the lensed galaxy is 9.3 Gyr away? How is it possible to measure that?

It's reddish orange color is because of the redshift? I see streams of blue bands which i guess is hot blue stars? But I guess that the lensed galaxy would be much more blue looking if it were much closer?

At cosmological distances, the "distance" (I used light travel time) is directly calculable from the redshift.

[C0ppert0p]

This is by far, the best example of an Einstein Ring, that i've ever seen

[Ann]

We are in-line with the distant lensed galaxy and the gravitational lens itself. I'd like to presume that there really are astronomers on that distant galaxy gazing at the lensed Milky Way. I wonder what they would be seeing right now, whatever "right now" means in this relativistic universe?

This is an unusual system. The source is at z=1.48 (9.3 Gyr) and the lens is at z=0.36 (4 Gyr), meaning that the lens is approximately centered between us and the source. In most cases where we observe Einstein rings, the lens is much closer to us than the source, meaning that anybody at the source would likely not see our galaxy lensed. This is a rare case where they might.

How do they know that the lensed galaxy is 9.3 Gyr away? How is it possible to measure that?

Distance is normally measured using redshift. Measuring redshift would not be possible if it was not for the presence of absorption lines in stellar spectra (and also in the spectra of galaxies).

Absorption lines in the solar spectrum. Image: N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF

---

Aborption lines are caused by elements absorbing specific wavelengths of light in a star's photosphere, leaving dark lines at specific places.

---

When a star or a galaxy is moving away from us, the dark spectral lines move toward the red part of the spectrum, like this:

Spectral lines that are 'neutral' (as recorded in the laboratory) vs. spectral lines that have been redshifted by different amounts, because the light source is moving away from us. The light from very distant galaxies is very redshifted.

---

So basically astronomers just study the spectral lines of a galaxy to find out how redshifted the lines are, and therefore, how far away the galaxy is.

It's reddish orange color is because of the redshift? I see streams of blue bands which i guess is hot blue stars? But I guess that the lensed galaxy would be much more blue looking if it were much closer?

Nearby galaxy NGC 7678. Image: Sloan Digital Sky Survey

---

Take a look at the APOD again. Inside the white oval is a fairly undistorted view of the lensed galaxy. The lensed galaxy is relatively similar to nearby galaxy NGC 7678. Both galaxies have an intrinsically yellow center (although the distant galaxy appears to lack a brilliantly bright core), and both of them have one blue arm.

Bear in mind that the light from the distant galaxy in the APOD is very redshifted, but one of the galaxy's arms is intrinsically bluer than the rest of it. The filter used for this Hubble image were F555W, which is this color: ███, and two infrared filters. What passed through the yellow-green filter was mapped as blue in the Hubble image.

Bear in mind that what we see as blue in the APOD was originally emitted as ultraviolet light, which has then been redshifted to yellow-green light by the time it reached the Earth.

Ann

[Ann]

We are in-line with the distant lensed galaxy and the gravitational lens itself. I'd like to presume that there really are astronomers on that distant galaxy gazing at the lensed Milky Way. I wonder what they would be seeing right now, whatever "right now" means in this relativistic universe?

This is an unusual system. The source is at z=1.48 (9.3 Gyr) and the lens is at z=0.36 (4 Gyr), meaning that the lens is approximately centered between us and the source. In most cases where we observe Einstein rings, the lens is much closer to us than the source, meaning that anybody at the source would likely not see our galaxy lensed. This is a rare case where they might.

Is that why the lensed galaxy looks so big and fat compared with the elliptical galaxy that is lensing it?

Lensed galaxies don't usually look that thick.

Abell 370: Galaxy Cluster Gravitational Lens. Image Credit: NASA, ESA, Hubble; Processing & Copyright: Rogelio Bernal Andreo (DeepSkyColors.com)

---

Ann

[beryllium732]

This is an unusual system. The source is at z=1.48 (9.3 Gyr) and the lens is at z=0.36 (4 Gyr), meaning that the lens is approximately centered between us and the source. In most cases where we observe Einstein rings, the lens is much closer to us than the source, meaning that anybody at the source would likely not see our galaxy lensed. This is a rare case where they might.

How do they know that the lensed galaxy is 9.3 Gyr away? How is it possible to measure that?

Distance is normally measured using redshift. Measuring redshift would not be possible if it was not for the presence of absorption lines in stellar spectra (and also in the spectra of galaxies).

Absorption lines in the solar spectrum. Image: N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF

---

Aborption lines are caused by elements absorbing specific wavelengths of light in a star's photosphere, leaving dark lines at specific places.

---

When a star or a galaxy is moving away from us, the dark spectral lines move toward the red part of the spectrum, like this:

Spectral lines that are 'neutral' (as recorded in the laboratory) vs. spectral lines that have been redshifted by different amounts, because the light source is moving away from us. The light from very distant galaxies is very redshifted.

---

So basically astronomers just study the spectral lines of a galaxy to find out how redshifted the lines are, and therefore, how far away the galaxy is.

It's reddish orange color is because of the redshift? I see streams of blue bands which i guess is hot blue stars? But I guess that the lensed galaxy would be much more blue looking if it were much closer?

APOD 5 July 2022 lensed galaxy detail.png

Nearby galaxy NGC 7678. Image: Sloan Digital Sky Survey

---

Take a look at the APOD again. Inside the white oval is a fairly undistorted view of the lensed galaxy. The lensed galaxy is relatively similar to nearby galaxy NGC 7678. Both galaxies have an intrinsically yellow center (although the distant galaxy appears to lack a brilliantly bright core), and both of them have one blue arm.

Bear in mind that the light from the distant galaxy in the APOD is very redshifted, but one of the galaxy's arms is intrinsically bluer than the rest of it. The filter used for this Hubble image were F555W, which is this color: ███, and two infrared filters. What passed through the yellow-green filter was mapped as blue in the Hubble image.

Bear in mind that what we see as blue in the APOD was originally emitted as ultraviolet light, which has then been redshifted to yellow-green light by the time it reached the Earth.

Ann

Always love your detailed answers! Thank you for explaining it all so vividly!

So in reality it's a very bright galaxy. It's really cool!