by Ann » Sun Feb 18, 2024 8:07 am
Hoag's Object is, of course, so incredibly strange and fascinating.
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 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:
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?
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.
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?
Ann
Hoag's Object is, of course, so incredibly strange and fascinating.
[float=left][img3="Hoag's Object: A Nearly Perfect Ring Galaxy
Image Credit: NASA, ESA, Hubble; Processing: Benoit Blanco"]https://apod.nasa.gov/apod/image/2402/Hoag_HubbleBlanco_1080.jpg[/img3][/float][float=right][attachment=1]APOD 18 February 2024 annotated.png[/attachment][c][size=85][color=#0040FF]I do think I can see orbital motion in the ring.[/color][/size][/c][/float]
[clear][/clear]
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:
[float=left][img3="A prototypical ring galaxy with a bar."]https://upload.wikimedia.org/wikipedia/commons/e/e8/CN_AC118_108.png[/img3][/float][float=right][attachment=0]Anatomy of a barred ring galaxy.png[/attachment][c][size=85][color=#0040FF]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.[/color][/size][/c][/float]
[clear][/clear]
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:
[float=left][img3="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"]https://www.universetoday.com/wp-content/uploads/2009/05/800px-am_0644-741.jpg[/img3][/float][float=right][img3="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."]https://astrophotographylens.com/cdn/shop/articles/Cartwheel_Galaxy.jpg?v=1683294852[/img3][/float]
[clear][/clear]
[float=left][img3="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."]https://bigthink.com/wp-content/uploads/2022/04/Arp_147.jpg?resize=768,633[/img3][/float][float=right][img3="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 "]https://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/Hubble_Interacting_Galaxy_Arp_148_%282008-04-24%29.jpg/1024px-Hubble_Interacting_Galaxy_Arp_148_%282008-04-24%29.jpg[/img3][/float]
[clear][/clear]
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?
[img3="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"]https://bigthink.com/wp-content/uploads/2022/04/734286main_potw1310a.jpg?resize=768,673[/img3]
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.
[float=left][img3="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. "]https://apod.nasa.gov/apod/image/2402/Hoag_HubbleBlanco_1080.jpg[/img3][/float][float=right][img3="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)"]https://www.eso.org/public/archives/images/screen/eso1611a.jpg[/img3][/float]
[clear][/clear]
Well, Hoag's Object is perhaps somewhat similar to a protoplanetary disk, but not really... :wink:
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?
[img3="Polar ring galaxy NGC 4650A. Credit: NASA, Hubble Heritage Project (STScI, AURA)"]https://stsci-opo.org/STScI-01EVTA48W22SJJ6HZZNFBDAPSK.jpg[/img3]
Ann