APOD: Hoag's Object: A Nearly Perfect Ring... (2019 Nov 27)

[APOD Robot]

Hoag's Object: A Nearly Perfect Ring Galaxy

Explanation: Is this one galaxy or two? This question came to light in 1950 when astronomer Arthur Hoag chanced upon this unusual extragalactic object. On the outside is a ring dominated by bright blue stars, while near the center lies a ball of much redder stars that are likely much older. Between the two is a gap that appears almost completely dark. How Hoag's Object formed, including its nearly perfectly round ring of stars and gas, remains unknown. Genesis hypotheses include a galaxy collision billions of years ago and the gravitational effect of a central bar that has since vanished. The featured photo was taken by the Hubble Space Telescope and recently reprocessed using an artificially intelligent de-noising algorithm. Observations in radio waves indicate that Hoag's Object has not accreted a smaller galaxy in the past billion years. Hoag's Object spans about 100,000 light years and lies about 600 million light years away toward the constellation of the Snake (Serpens). Many galaxies far in the distance are visible toward the right, while coincidentally, visible in the gap at about seven o'clock, is another but more distant ring galaxy.

<< Previous APOD

This Day in APOD

Next APOD >>

[BDanielMayfield]

Hmm. As ring galaxies are quite rare, finding yet another distant ring galaxy perfectly framed inside another ring galaxy's gap is rather extraordinary. I wonder what could have caused ring galaxies to have a preference for forming in this particular direction?

Bruce

[JohnD]

Is that another similar object visible thouth Hoag's ring gap? It looks more like a galaxy with several bright star-forming areas in the disc, not the uniform appearnce of Hoag.
John

[Ann]

Is that another similar object visible thouth Hoag's ring gap? It looks more like a galaxy with several bright star-forming areas in the disc, not the uniform appearnce of Hoag.
John

Click to view full size image

Hoag's Object with ring galaxy seen inside its ring,
and barred galaxy with bar-end enhancements seen in its ring.
NASA, ESA, Hubble; Processing: Benoit Blanco

Click to view full size image

Barred galaxy NGC 936 with bar-end enhancements.
ESO - http://www.eso.org/public/images/potw1009a/

There is another ring galaxy in today's APOD, seen inside the ring of Hoag's Object at 7 o'clock. There is also another deceptively ring galaxy-like object at 2 o'cloc, seen through the ring itself.

But this galaxy at 2 o'clock is almost certainly not a ring galaxy. Instead, it is most likely a barred galaxy with bar-end enhancements, slightly similar to NGC 936. According to the caption of today's APOD, there is speculation that Hoag's Object might have formed when Hoag's object lost its bar, and its bar-end enhancements turned into a ring.

Well maybe, maybe not.

Ann

[MottyGlix]

In one of her videos, Dr Rebecca Smethurst discusses mechanisms for how Hoag's Object may have formed. I am especially impressed by the work of Elena Yannikova quoted there. That speaks of a gravitational effect that, over time, would have moved all the stars or star-forming gas in a certain range of radii from the center either hubward or rimward within the Object. I recall viewing this in this YouTube video

Click to play embedded YouTube video.

See, particularly, 11:33 to 13:55.

[Alex515]

Hi,

I have the impression that the Deep Image Prior algorithm used to denoise the signal adds some kind of small filaments which I doubt to correspond to real filaments. What do you think ?

Alex

[JohnD]

A gap in a ring often implies a gravitational efect from another body, larger, or with more gravity, than the ring objects. See, Saturn and Jupiter. As the ring objects of Hoag are stars, not ice dust, the other body must be something extremely dense, and as nothing is seen, dark. That makes me think, Black Hole. Could there be a BH in the gap, the relic of a previous galactic merger?

[neufer]

Hoag ALgorithmic computer

---

<<The Eye of Providence (or the all-seeing eye of God) is a symbol showing an eye often surrounded by rays of light or a glory. Seventeenth-century depictions of the Eye of Providence sometimes show it surrounded by clouds or sunbursts.

It represents the eye of God watching over humanity.>>

Does it read lips?

[orin stepanek]

Hoag_HubbleBlanco_1080.jpg (21.01 KiB) Viewed 9260 times

Something unusual must have happened in this galaxies past to create this marvelous almost perfect circle! Pretty big
central region! It really looks like a wheel!

[Chris Peterson]

Hmm. As ring galaxies are quite rare, finding yet another distant ring galaxy perfectly framed inside another ring galaxy's gap is rather extraordinary. I wonder what could have caused ring galaxies to have a preference for forming in this particular direction?

While there is evidence of galaxy orientation alignment preferences over vast cosmological distances, taken in small numbers the orientations are still very close to random. It's unlikely that we're seeing anything more than coincidental alignment here, both in position and orientation.

[Ann]

Let's look at some cool ring galaxies!

Click to view full size image

Infrared image of ring galaxy NGC 1291.
NASA/JPL-Caltech - http://photojournal.jpl.nasa.gov/jpeg/PIA18847.jpg

Click to view full size image

Incredible ring galaxy Mayall's Object.
NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration,
and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

Click to view full size image

Polar ring galaxy 4650A.The Hubble Heritage Team
(AURA/STScI/NASA)
http://hubblesite.org/newscenter/archiv ... 16/image/a

Click to view full size image

Lenticular ring galaxy, the Cartwheel galaxy.
#ESA/#Hubble & #NASA

Click to play embedded YouTube video.

Let's look at a simulation of the formation of a ring galaxy:


Ann

[BDanielMayfield]

Hmm. As ring galaxies are quite rare, finding yet another distant ring galaxy perfectly framed inside another ring galaxy's gap is rather extraordinary. I wonder what could have caused ring galaxies to have a preference for forming in this particular direction?

While there is evidence of galaxy orientation alignment preferences over vast cosmological distances, taken in small numbers the orientations are still very close to random. It's unlikely that we're seeing anything more than coincidental alignment here, both in position and orientation.

My science side is almost totally fine with that explanation, so yeah, this is probably just a random chance alignment. I just wonder, due to the rareness of such objects if there could be some natural process at work making this view less unlikely.

But my other side, the side I can't display here much due to the site's ban on religious praise, just loves this APOD.

Bruce

[Chris Peterson]

Hmm. As ring galaxies are quite rare, finding yet another distant ring galaxy perfectly framed inside another ring galaxy's gap is rather extraordinary. I wonder what could have caused ring galaxies to have a preference for forming in this particular direction?

While there is evidence of galaxy orientation alignment preferences over vast cosmological distances, taken in small numbers the orientations are still very close to random. It's unlikely that we're seeing anything more than coincidental alignment here, both in position and orientation.

My science side is almost totally fine with that explanation, so yeah, this is probably just a random chance alignment. I just wonder, due to the rareness of such objects if there could be some natural process at work making this view less unlikely.

Well, if there were some other [scientific] process at work, I think we'd expect to see other galaxies in that region of the sky (say, inside a 1° box or smaller) showing an orientation bias, but I don't think that's the case. And keep in mind that this is very observer location dependent. Any pair of galaxies whose planes are parallel to each other will present a similar view from the right locations in space.

[BDanielMayfield]

While there is evidence of galaxy orientation alignment preferences over vast cosmological distances, taken in small numbers the orientations are still very close to random. It's unlikely that we're seeing anything more than coincidental alignment here, both in position and orientation.

My science side is almost totally fine with that explanation, so yeah, this is probably just a random chance alignment. I just wonder, due to the rareness of such objects if there could be some natural process at work making this view less unlikely.

Well, if there were some other [scientific] process at work, I think we'd expect to see other galaxies in that region of the sky (say, inside a 1° box or smaller) showing an orientation bias, but I don't think that's the case. And keep in mind that this is very observer location dependent. Any pair of galaxies whose planes are parallel to each other will present a similar view from the right locations in space.

Just for curiosity's sake, I wonder what the view looks like in the direct opposite direction, about 180 degrees away from Hoag's object? Almost certainly nothing like this view I'm almost, almost, nearly 100% certain, but it wouldn't hurt to look would it?

If by some fantastic coincidence there was a ring galaxy (or even two) on the direct other side of the sky wouldn't that be a trip! (wheels a turning') Whoever looks might just discover the Axis of the Universe

Nah. But hey, again, it wouldn't hurt to look, and post image(s) of the view.

[Chris Peterson]

My science side is almost totally fine with that explanation, so yeah, this is probably just a random chance alignment. I just wonder, due to the rareness of such objects if there could be some natural process at work making this view less unlikely.

Well, if there were some other [scientific] process at work, I think we'd expect to see other galaxies in that region of the sky (say, inside a 1° box or smaller) showing an orientation bias, but I don't think that's the case. And keep in mind that this is very observer location dependent. Any pair of galaxies whose planes are parallel to each other will present a similar view from the right locations in space.

Just for curiosity's sake, I wonder what the view looks like in the direct opposite direction, about 180 degrees away from Hoag's object? Almost certainly nothing like this view I'm almost, almost, nearly 100% certain, but it wouldn't hurt to look would it?

I'd expect that if we traveled in a straight path towards these galaxies, and continued past the farthest one until we were the same distance from it as we now are from the nearer one, the view would be almost identical.

[neufer]

Lenticular ring galaxy, the Cartwheel galaxy. ESA/Hubble & NASA

---

.
Let's look at a simulation of the formation of a ring galaxy:
.

Click to play embedded YouTube video.

.
Let's look at some cool ring galaxies!

The extended (Chandra) X-ray emission (shown below) from the Cartwheel galaxy
to its small spiral galactic neighbor sure suggests a head-on collision.

Note that the small spiral galactic neighbor looks like it might also be reverberating as a small ring-galaxy.

So is the small ring galaxy in the Hoag's Object APOD not a "coincidental distant object"
but rather the hit-and-run perpetrator/penetrator.

The Cartwheel galaxy in different light spectra (X-ray, ultraviolet, visible, and infrared). The image combines data from four different space-based observatories: the Chandra X-ray Observatory (purple), the Galaxy Evolution Explorer (ultraviolet/blue), the Hubble Space Telescope (visible/green), and the Spitzer Space Telescope (infrared/red). Image is 160 arcsec across. RA 00h 37m 41.10s Dec −33° 42′ 58.80″ in Sculptor. Credit: NASA/JPL/Caltech/P.Appleton et al. X-ray: NASA/CXC/A.Wolter & G.Trinchieri et al.

---

<<The Cartwheel Galaxy (also known as ESO 350-40 or PGC 2248) is a lenticular galaxy and ring galaxy about 500 million light-years away in the constellation Sculptor. It is an estimated 150,000 light-years diameter, and has a mass of about 2.9–4.8 × 10⁹ solar masses; its outer ring has a circular velocity of 217 km/s. The Cartwheel galaxy shows non-thermal radio and optical spokes, but they are not the same spokes.

The galaxy was once a normal spiral galaxy before it apparently underwent a head-on collision with a smaller companion approximately 200 million years ago (i.e., 200 million years prior to the image). When the nearby galaxy passed through the Cartwheel Galaxy, the force of the collision caused a powerful shock wave through the galaxy, like a rock being tossed into a sandbed. Moving at high speed, the shock wave swept up gas and dust, creating a starburst around the galaxy's center portion that were unscathed. This explains the bluish ring around the center, brighter portion. It can be seen that the galaxy is beginning to retake the form of a normal spiral galaxy, with arms spreading out from a central core.

The unusual shape of the Cartwheel Galaxy may be due to a collision with a smaller galaxy such as those in the lower left of the image. The most recent star burst (star formation due to compression waves) has lit up the Cartwheel rim, which has a diameter larger than the Milky Way. Star formation via starburst galaxies, such as the Cartwheel Galaxy, results in the formation of large and extremely luminous stars. When massive stars explode as supernovas, they leave behind neutron stars and black holes. Some of these neutron stars and black holes have nearby companion stars, and become powerful sources of X-rays as they pull matter off their companions (also known as ultra and hyperluminous X-ray sources).[10] The brightest X-ray sources are likely black holes with companion stars, and appear as the white dots that lie along the rim of the X-ray image. The Cartwheel contains an exceptionally large number of these black hole binary X-ray sources, because many massive stars formed in the ring.>>

[astroarchitect1]

Just wondering... being that it's 600 million miles away, how do they know that the older, redder cluster of stars in what looks like the middle of the ring is actually in the middle of the ring and not simply aligned with our point of view and at a different distance? It's not like we can look at it from another place in the universe and see no parallax shift...

[Chris Peterson]

Just wondering... being that it's 600 million miles away, how do they know that the older, redder cluster of stars in what looks like the middle of the ring is actually in the middle of the ring and not simply aligned with our point of view and at a different distance? It's not like we can look at it from another place in the universe and see no parallax shift...

The core and the ring have exactly the same redshift, z = 0.04244, which places them at the same distance from us.

[sillyworm 2]

I'm leaning toward the theory that there were once bars and they have dissipated.

[BDanielMayfield]

I'm leaning toward the theory that there were once bars and they have dissipated.

What! My Axis of the Universe idea wasn't silly enough? Darn.

The dissipated bars theory was actually a scientifically proposed explanation for a time, but problems with it lead to better working theories. If you haven't already watched it see the video in this post:

In one of her videos, Dr Rebecca Smethurst discusses mechanisms for how Hoag's Object may have formed. I am especially impressed by the work of Elena Yannikova quoted there. That speaks of a gravitational effect that, over time, would have moved all the stars or star-forming gas in a certain range of radii from the center either hubward or rimward within the Object. I recall viewing this in this YouTube video

Click to play embedded YouTube video.

See, particularly, 11:33 to 13:55.

Thank you for sharing that MottyGlix. It is excellent.

Bruce

[edgardine]

The extended (Chandra) X-ray emission (shown below) from the Cartwheel galaxy
to its small spiral galactic neighbor sure suggests a head-on collision.

Note that the small spiral galactic neighbor looks like it might also be reverberating as a small ring-galaxy.

So is the small ring galaxy in the Hoag's Object APOD not a "coincidental distant object"
but rather the hit-and-run perpetrator/penetrator.

Thank you Ann and Neufer for these suggestions.
Do we know the Redshift of the small ring galaxy in the Hoag's Object APOD ?

[neufer]

The extended (Chandra) X-ray emission (shown below) from the Cartwheel galaxy
to its small spiral galactic neighbor sure suggests a head-on collision.

Note that the small spiral galactic neighbor looks like it might also be reverberating as a small ring-galaxy.

So is the small ring galaxy in the Hoag's Object APOD not a "coincidental distant object"
but rather the hit-and-run perpetrator/penetrator.

Thank you Ann and Neufer for these suggestions.

Do we know the Redshift of the small ring galaxy in the Hoag's Object APOD ?

I'd sorta like to know that myself, edgardine.
..................................................................
From its size alone one might assume it is a "Hoag's Object" roughly ten times more distant: z ~ 0.4244

However, for it to be as red as it is entirely from cosmological redshift it would have to be z ~ 4.244

Coincidence or not, it is probably red primarily due to (supernova) dust generated by the collision itself.

The core and the ring [of Hoag's Object] have exactly the same redshift,
z = 0.04244, which places them at the same distance from us.

[Ann]

The extended (Chandra) X-ray emission (shown below) from the Cartwheel galaxy
to its small spiral galactic neighbor sure suggests a head-on collision.

Note that the small spiral galactic neighbor looks like it might also be reverberating as a small ring-galaxy.

So is the small ring galaxy in the Hoag's Object APOD not a "coincidental distant object"
but rather the hit-and-run perpetrator/penetrator.

Thank you Ann and Neufer for these suggestions.

Do we know the Redshift of the small ring galaxy in the Hoag's Object APOD ?

I'd sorta like to know that myself, edgardine.
..................................................................
From its size alone one might assume it is a "Hoag's Object" roughly ten times more distant: z ~ 0.4244

However, for it to be as red as it is entirely from cosmological redshift it would have to be z ~ 4.244

Coincidence or not, it is probably red primarily due to (supernova) dust generated by the collision itself.

The core and the ring [of Hoag's Object] have exactly the same redshift,
z = 0.04244, which places them at the same distance from us.

I seem to have misplaced my doctoral diploma, so until I can find it, I must reluctantly ask you to regard me as an amateur.
Heavens! Me!!!

So according to my expertise - I mean, my amateur opinion - the small red galaxy inside Hoag's Object is too small and red to be easily thought of as equidistant with Hoag's Object. Applying the theorem of Occam's Razor, I must instead conclude that the small red ring galaxy seen inside Hoag's Object appears small and red to us because it is much more distant than Hoag's Object itself.

However, my main concern over the idea that Hoag's Object and the small red ring galaxy seen inside are related is that both these ring galaxies are so perfectly shaped and undisturbed. No major collision must have perturbed their shapes for several Myr and possibly Gyr.

Clears throat:

So my carefully considered conclusion is that these two galaxies are unrelated.

Steps down from pulpit and removes wig. Audience goes, Aaaaahhhh!!!!

Ann

[neufer]

From its size alone one might assume it is a "Hoag's Object" roughly ten times more distant: z ~ 0.4244

However, for it to be as red as it is entirely from cosmological redshift it would have to be z ~ 4.244

Coincidence or not, it is probably red primarily due to (supernova) dust generated by the collision itself.

The core and the ring [of Hoag's Object] have exactly the same redshift,
z = 0.04244, which places them at the same distance from us.

---

So according to my expertise - I mean, my amateur opinion - the small red galaxy inside Hoag's Object is too small and red to be easily thought of as equidistant with Hoag's Object. Applying the theorem of Occam's Razor, I must instead conclude that the small red ring galaxy seen inside Hoag's Object appears small and red to us because it is much more distant than Hoag's Object itself.

However, my main concern over the idea that Hoag's Object and the small red ring galaxy seen inside are related is that both these ring galaxies are so perfectly shaped and undisturbed. No major collision must have perturbed their shapes for several Myr and possibly Gyr. Clears throat:

So my carefully considered conclusion is that these two galaxies are unrelated.

[Chris Peterson]

Do we know the Redshift of the small ring galaxy in the Hoag's Object APOD ?

I looked through a bunch of references and didn't find any record of this object having been examined spectroscopically.