APOD: Galaxies in the River (2023 Jul 27)

[APOD Robot]

Galaxies in the River

Explanation: Large galaxies grow by eating small ones. Even our own galaxy engages in a sort of galactic cannibalism, absorbing small galaxies that are too close and are captured by the Milky Way's gravity. In fact, the practice is common in the universe and illustrated by this striking pair of interacting galaxies from the banks of the southern constellation Eridanus, The River. Located over 50 million light years away, the large, distorted spiral NGC 1532 is seen locked in a gravitational struggle with dwarf galaxy NGC 1531, a struggle the smaller galaxy will eventually lose. Seen nearly edge-on, spiral NGC 1532 spans about 100,000 light-years. The merging galaxies are captured in this sharp image from the Dark Energy Camera mounted on the National Science Foundation’s Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile. The NGC 1532/1531 pair is thought to be similar to the well-studied system of face-on spiral and small companion known as M51.

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[shaileshs]

I'm wondering if they are interacting with a bright galaxy visible towards lower left corner (7-7:30 position on a 12 hour clock dial) ?

[Ann]

I'm wondering if they are interacting with a bright galaxy visible towards lower left corner (7-7:30 position on a 12 hour clock dial) ?

My software shows no galaxy there. But there is a bright star, HD 26799, in the position you indicated. The star is magnitude 7.048 according to my software, and NGC 1532 is magnitude 9.8 (10.69 in B magnitude), so the star is at least two magnitudes brighter than the galaxy in our skies.

Ann

[AVAO]

I'm wondering if they are interacting with a bright galaxy visible towards lower left corner (7-7:30 position on a 12 hour clock dial) ?

I think, the galaxy is IC 2041!

https://de.wikipedia.org/wiki/IC_2041

[De58te]

So I take it that the dwarf galaxy is the white oval shape above center and the large galaxy is edge on. What I like to know is which direction is the collision? Is the dwarf plunging downwards like a head on collision, or, is it hovering in place like a helicopter but it is being cannibalized from the right side like a giant vacuum cleaner is sucking out the dust which is turning blue as new stars form to eventually settle down in the long arm out in the front?

[Chris Peterson]

So I take it that the dwarf galaxy is the white oval shape above center and the large galaxy is edge on. What I like to know is which direction is the collision? Is the dwarf plunging downwards like a head on collision, or, is it hovering in place like a helicopter but it is being cannibalized from the right side like a giant vacuum cleaner is sucking out the dust which is turning blue as new stars form to eventually settle down in the long arm out in the front?

Two galaxies cannot remain stationary with respect to each other, or "hover". These two galaxies are in orbit around one another. The shape of those orbits (of which that of the lower mass galaxy is most interesting) is probably partly determinable from looking at redshift measurements.

[Ann]

Galaxies in the River. Image Credit & License: CTIO/NOIRLab/DOE/NSF/AURA; R. Colombari, M. Zamani & D. de Martin (NSF’s NOIRLab)

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NGC 1532 is an interesting-looking galaxy. However, the caption compares it with M51, the Whirlpool Galaxy. I don't think that is correct at all. M51 is a smallish unbarred galaxy, considerably smaller than the Milky Way, whereas NGC 1532 is a large barred galaxy, twice as large as our own galaxy.

I think NGC 1532 is somewhat similar to NGC 6872:

NGC 6872 (center) with IC 4970 (above). Credit: ESO/VLT, Judy Schmidt

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Admittedly NGC 6872 is much larger than NGC 1532. That is because the arms of NGC 6872 are completely "outstretched" instead of being wrapped around the galactic center. Still, NGC 1532 also appears to be somewhat "elongated" with at least one arm strongly affected by tidal effects.

Anyway, NGC 1532 is a fascinating galaxy!

Ann

[johnnydeep]

I'm wondering if they are interacting with a bright galaxy visible towards lower left corner (7-7:30 position on a 12 hour clock dial) ?

I think, the galaxy is IC 2041!

https://de.wikipedia.org/wiki/IC_2041

Yup - that's almost certainly the same object/galaxy we see so clearly in this APOD!

[orin stepanek]

Galaxies eat each other; yet there are so many of them.

[Ann]

I'm wondering if they are interacting with a bright galaxy visible towards lower left corner (7-7:30 position on a 12 hour clock dial) ?

I think, the galaxy is IC 2041!

https://de.wikipedia.org/wiki/IC_2041

Yup - that's almost certainly the same object/galaxy we see so clearly in this APOD!

Sorry, shaileshs. I said to you that there were no galaxies there, because I thought that IC 2041 was too small to be called a "bright galaxy"!

Ann

[shaileshs]

I think, the galaxy is IC 2041!

https://de.wikipedia.org/wiki/IC_2041

Yup - that's almost certainly the same object/galaxy we see so clearly in this APOD!

Sorry, shaileshs. I said to you that there were no galaxies there, because I thought that IC 2041 was too small to be called a "bright galaxy"!

Ann

Ann, please check the photo in that published APOD. Check 7:30 clock (hour hand) position. That's the one I'm referring to. I couldn't embed the image but I've attached it. Check marked galaxy (marked by red circle). Thanks.

[Ann]

Yup - that's almost certainly the same object/galaxy we see so clearly in this APOD!

Sorry, shaileshs. I said to you that there were no galaxies there, because I thought that IC 2041 was too small to be called a "bright galaxy"!

Ann

Ann, please check the photo in that published APOD. Check 7:30 clock (hour hand) position. That's the one I'm referring to. I couldn't embed the image but I've attached it. Check marked galaxy (marked by red circle). Thanks.

Click to view full size image

Yes, I understand that now. As I said, I was looking for something much larger and brighter, and when I saw a bright star in (more or less) the position you referred to, I thought that was it - a bright light source!

But I was wrong. I'm glad johnnydeep could help you!

Ann