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Posted: **Sun Feb 18, 2024 5:06 am**

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 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.

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Posted: **Sun Feb 18, 2024 8:07 am**

Hoag's Object is, of course, so incredibly strange and fascinating.

: Hoag's Object: A Nearly Perfect Ring Galaxy Image Credit: NASA, ESA, Hubble; Processing: Benoit Blanco

I do think I can see orbital motion in the ring.

To see what makes Hoag's Object so strange, let's compare it with a few other ring galaxies. Let's start with a prototypical ring galaxy whose designation and photographer I don't know:

: A prototypical ring galaxy with a bar.

A barred ring galaxy has a nucleus, a bar and a ring.
The bar is divided in two parts, one on each side of the nucleus.
The bar ends typically touch the ring.

Compared with the prototypical barred ring galaxy, Hoag's Object has no bar, and no part of the ring appears to touch or have any connection with the "nucleus" (or rather, with the central elliptical body).

There is a whole zoo out there of ring galaxies! Let's look at a few:

: Ring galaxy AM 0644-741. Talk about having a disturbed ring! Look closely, and you can see a faint connection between the ring and the yellow elliptical component. We may also note that there is definitely more star formation in this ring than in the ring of Hoag's Object. Credit: Hubble

: The Cartwheel galaxy in optical light by Hubble at left and in infrared light by JWST at right. The Cartwheel galaxy got its unique shape when a smaller galaxy smashed right through the disk of it, causing the disk to expand like a tsunami.

: Oops, the ring came loose! Actually, this is a pair of galaxies that have just collided. Collectively, they are known as Arp 147. The galaxy on the left plunged through the galaxy on the right. The intruder lost its gas and became a lenticular galaxy, whereas the the galaxy on the right became distorted into a ring shape and is undergoing a raging wildfire of star formation. The orange-brown area at lower left in the ring galaxy is probably the original nucleus.

: The scene of the crime that created Arp 147 may have looked like this. This pair is known as Mayall's Object, but it is also designated Arp 148. One galaxy is plunging right through another galaxy, turning its victim into a ring as it does so. The orange patch located approximately in the center of the ring galaxy is its nucleus. Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans

What will happen to Mayall's Object? Is the intruder passing through with such speed and force that it is going to continue its journey away from its hapless ring-shaped victim? Will the ring-shaped component of Mayall's Object end up as Zwicky II 28, an apparently nucleus-less ring-shaped galaxy all on its own?

: Zwicky II 28 appears to lack a nucleus. However, the bright patch at upper left if probably the nucleus. Note the extremely high levels of star formation. Was this galaxy hit by another galaxy that somehow got away? Credit: ESA/Hubble and NASA; Acknowledgment: Judy Schmidt

I have two thoughts on what could have caused the perfect shape of Hoag's Object. The first is a protoplanetary disk. When a planet forms in a protoplanetary disk, it clears out a perfect circular gap in the disk.

: Is Hoag's Object like a protoplanetary disk? And is the reddened ring galaxy in the gap of Hoag's Object the 'planet' that clared out the gap? I guess not.

: A protoplanetary disk around young star TW Hydrae with gaps carved by planets. Credit: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO)

Well, Hoag's Object is perhaps somewhat similar to a protoplanetary disk, but not really...

But consider polar ring galaxy NGC 4650A. We see it from the side. If we saw it face on, would it resemble Hoag's Object? Maybe?

: Polar ring galaxy NGC 4650A. Credit: NASA, Hubble Heritage Project (STScI, AURA)

Ann

Posted: **Sun Feb 18, 2024 11:16 am**

Ann wrote: ↑Sun Feb 18, 2024 8:07 am Hoag's Object is, of course, so incredibly strange and fascinating.

Hoag's Object: A Nearly Perfect Ring Galaxy Image Credit: NASA, ESA, Hubble; Processing: Benoit Blanco
APOD 18 February 2024 annotated.png
I do think I can see orbital motion in the ring.

To see what makes Hoag's Object so strange, let's compare it with a few other ring galaxies. Let's start with a prototypical ring galaxy whose designation and photographer I don't know:

A prototypical ring galaxy with a bar.
Anatomy of a barred ring galaxy.png
A barred ring galaxy has a nucleus, a bar and a ring.
The bar is divided in two parts, one on each side of the nucleus.
The bar ends typically touch the ring.

Compared with the prototypical barred ring galaxy, Hoag's Object has no bar, and no part of the ring appears to touch or have any connection with the "nucleus" (or rather, with the central elliptical body).

There is a whole zoo out there of ring galaxies! Let's look at a few:

Ring galaxy AM 0644-741. Talk about having a disturbed ring! Look closely, and you can see a faint connection between the ring and the yellow elliptical component. We may also note that there is definitely more star formation in this ring than in the ring of Hoag's Object. Credit: Hubble
The Cartwheel galaxy in optical light by Hubble at left and in infrared light by JWST at right. The Cartwheel galaxy got its unique shape when a smaller galaxy smashed right through the disk of it, causing the disk to expand like a tsunami.

Oops, the ring came loose! Actually, this is a pair of galaxies that have just collided. Collectively, they are known as Arp 147. The galaxy on the left plunged through the galaxy on the right. The intruder lost its gas and became a lenticular galaxy, whereas the the galaxy on the right became distorted into a ring shape and is undergoing a raging wildfire of star formation. The orange-brown area at lower left in the ring galaxy is probably the original nucleus.
The scene of the crime that created Arp 147 may have looked like this. This pair is known as Mayall's Object, but it is also designated Arp 148. One galaxy is plunging right through another galaxy, turning its victim into a ring as it does so. The orange patch located approximately in the center of the ring galaxy is its nucleus. Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans

What will happen to Mayall's Object? Is the intruder passing through with such speed and force that it is going to continue its journey away from its hapless ring-shaped victim? Will the ring-shaped component of Mayall's Object end up as Zwicky II 28, an apparently nucleus-less ring-shaped galaxy all on its own?

Zwicky II 28 appears to lack a nucleus. However, the bright patch at upper left if probably the nucleus. Note the extremely high levels of star formation. Was this galaxy hit by another galaxy that somehow got away? Credit: ESA/Hubble and NASA; Acknowledgment: Judy Schmidt

I have two thoughts on what could have caused the perfect shape of Hoag's Object. The first is a protoplanetary disk. When a planet forms in a protoplanetary disk, it clears out a perfect circular gap in the disk.

Is Hoag's Object like a protoplanetary disk? And is the reddened ring galaxy in the gap of Hoag's Object the 'planet' that clared out the gap? I guess not.
A protoplanetary disk around young star TW Hydrae with gaps carved by planets. Credit: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO)

Well, Hoag's Object is perhaps somewhat similar to a protoplanetary disk, but not really...

But consider polar ring galaxy NGC 4650A. We see it from the side. If we saw it face on, would it resemble Hoag's Object? Maybe?

Polar ring galaxy NGC 4650A. Credit: NASA, Hubble Heritage Project (STScI, AURA)

Ann

Fascinating Ann

https://en.wikipedia.org/wiki/File:CN_AC118_108.png

According to Wikipedia:

CN AC118 108 is a galaxy about 3760 million light-years away in Pandora's cluster. It has a peculiar ring shape. Picture by Hubble Space Telsecope.

3.76 billion light years away?? Blows my mind.

Posted: **Sun Feb 18, 2024 11:48 am**

Rauf wrote: ↑Sun Feb 18, 2024 11:16 am
Fascinating Ann

https://en.wikipedia.org/wiki/File:CN_AC118_108.png

According to Wikipedia:

CN AC118 108 is a galaxy about 3760 million light-years away in Pandora's cluster. It has a peculiar ring shape. Picture by Hubble Space Telsecope.
3.76 billion light years away?? Blows my mind.

Thanks Rauf! You found it for me!

: CN AC118 108. Credit: Hubble Space Telescope/Swuty

Ann

Posted: **Sun Feb 18, 2024 2:33 pm**

I love this beautiful odd ball (only 1/1000 galaxies are ring galaxies apparently), but I wish we had a better picture. Of course, it's more than 200 times farther away than Andromeda (600 Mly versus 2.5 Mly). How would this look to JWST I wonder?

Posted: **Sun Feb 18, 2024 2:48 pm**

How do you fit these shapes into your dark matter conjecture?

Posted: **Sun Feb 18, 2024 3:03 pm**

Roy wrote: ↑Sun Feb 18, 2024 2:48 pm How do you fit these shapes into your dark matter conjecture?

AFAIK nobody has done the sort of radial velocity or gravitational lensing measurements that are used to map dark matter halos around galaxies. And nobody has developed a solid testable (or tested) hypothesis as to the mechanism by which ring galaxies form, and therefore it hasn't been modeled yet... with or without dark matter.

Posted: **Sun Feb 18, 2024 7:05 pm**

That's a spectacular collection of peculiar galaxies @Ann. Or should that be a peculiar collection of spectacular galaxies?

Posted: **Sun Feb 18, 2024 7:15 pm**

Knight of Clear Skies wrote: ↑Sun Feb 18, 2024 7:05 pm That's a spectacular collection of peculiar galaxies @Ann. Or should that be a peculiar collection of spectacular galaxies?

Don't forget the spectacular collection of spectacular galaxies, and the peculiar collection of peculiar galaxies. Honestly, I'd like to see both of those collections as well!

Posted: **Mon Feb 19, 2024 5:48 am**

johnnydeep wrote: ↑Sun Feb 18, 2024 7:15 pm
Knight of Clear Skies wrote: ↑Sun Feb 18, 2024 7:05 pm That's a spectacular collection of peculiar galaxies @Ann. Or should that be a peculiar collection of spectacular galaxies?
Don't forget the spectacular collection of spectacular galaxies, and the peculiar collection of peculiar galaxies. Honestly, I'd like to see both of those collections as well!

I don't have a collection for you, Johnny, but I have a peculiar one for you, NGC 2537!

: NGC 2537 in ultraviolet light by GALEX. Credit: NASA/JPL-Caltech.

: NGC 2537 through green, red and infrared filters. Credit: SDSS/Donald Pelletier.

: This is what it looks like through a 606 nm (orange) filter by Hubble. Credit: NASA/Meli thev

NGC 2537 is known as the Bear Claw galaxy. Did Ursa Major, the Big Bear, get lost on his way across the heavens and leave his paw print in another constellation? Possibly, because NGC 2537 is in Lynx, which is right next to the Big Bear!

: The Big Bear is located immediately to the 'left' of Lynx. Note the constellation of Lynx right next to the big bear's front paw. Hand-colored etching by Sidney Hall, circa 1825.

Ann

Posted: **Mon Feb 19, 2024 9:22 am**

Ann wrote: ↑Mon Feb 19, 2024 5:48 am
johnnydeep wrote: ↑Sun Feb 18, 2024 7:15 pm
Knight of Clear Skies wrote: ↑Sun Feb 18, 2024 7:05 pm That's a spectacular collection of peculiar galaxies @Ann. Or should that be a peculiar collection of spectacular galaxies?
Don't forget the spectacular collection of spectacular galaxies, and the peculiar collection of peculiar galaxies. Honestly, I'd like to see both of those collections as well!
I don't have a collection for you, Johnny, but I have a peculiar one for you, NGC 2537!

This is what it looks like through a 606 nm (orange) filter by Hubble. Credit: NASA/Meli thev

Ann

Is that a figure of eight I see at 8 o'clock from the centre of NGC 2537??

And what about the smoke ring in the bottom right??

Posted: **Mon Feb 19, 2024 10:29 am**

JimB wrote: ↑Mon Feb 19, 2024 9:22 am
Ann wrote: ↑Mon Feb 19, 2024 5:48 am
johnnydeep wrote: ↑Sun Feb 18, 2024 7:15 pm

Don't forget the spectacular collection of spectacular galaxies, and the peculiar collection of peculiar galaxies. Honestly, I'd like to see both of those collections as well!
I don't have a collection for you, Johnny, but I have a peculiar one for you, NGC 2537!

This is what it looks like through a 606 nm (orange) filter by Hubble. Credit: NASA/Meli thev

Ann
Is that a figure of eight I see at 8 o'clock from the centre of NGC 2537??

And what about the smoke ring in the bottom right??

They are photographic artifacts, probably reflections in the mirror of the telescope (but I'll leave it to Chris to describe the exact details

).

But the reflections look cool, don't they? Imagine if we could actually call the Bear Claw Galaxy the Figure Eight Galaxy instead!

Ann

Posted: **Mon Feb 19, 2024 12:55 pm**

Thanks, Ann. The peculiar "Bear Claw" galaxy sort of looks like one C-shaped galaxy about to swallow a smaller oblong one. Or maybe it's more of a single spiral that looks like a lowercase "e":

Posted: **Mon Feb 19, 2024 1:26 pm**

johnnydeep wrote: ↑Mon Feb 19, 2024 12:55 pm Thanks, Ann. The peculiar "Bear Claw" galaxy sort of looks like one C-shaped galaxy about to swallow a smaller oblong one. Or maybe it's more of a single spiral that looks like a lowercase "e":

Click to view full size image

The Pacman galaxy?

: Click to view full size image

Ann

Posted: **Mon Feb 19, 2024 1:31 pm**

Ann wrote: ↑Mon Feb 19, 2024 1:26 pm
johnnydeep wrote: ↑Mon Feb 19, 2024 12:55 pm Thanks, Ann. The peculiar "Bear Claw" galaxy sort of looks like one C-shaped galaxy about to swallow a smaller oblong one. Or maybe it's more of a single spiral that looks like a lowercase "e":

Click to view full size image

The Pacman galaxy?

Click to view full size image

Ann

Yeah, I thought of that comparison too. And we already have a Pacman Nebula, NGC 281:

: The PacMan Nebula (NGC 281) was created with Ha, OIII, and SII filters using the Hubble Palette. Imaging Telescope: Explore Scientific 127mm ED Refractor (952 focal length) Field Flattener: HoTech 2 inch SCA Field Flattener Mount: Celestron CGX Polar Alignment: QHYCCD PoleMaster Imaging Camera: ZWO ASI1600MM-Cool Ha=61x180s OIII=115x120s SII=60x180s Total Time: 9.9 hours Gain: 139, Offset: 21 Guide scope: Orion ST80 Guide Camera: Lodestar X2 Guide Software: PHD2 Calibration Frames: Darks: 50, Bias: 50, Flats: 50 Capture software: Sequence Generator Pro (SGP) Stacking software: PixInsight Post Processing: PixInsight, PhotoShop Dew Shield, Dew Heater Strip

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APOD: Hoag's Object: A Nearly Perfect... (2024 Feb 18)

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Re: APOD: Hoag's Object: A Nearly Perfect... (2024 Feb 18)

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