APOD: M100: A Grand Design Spiral Galaxy (2024 May 02)

[johnnydeep]

I just told you that I don't necessarily always trust Wikipedia, but now I'm going to quote Wikipedia anyway to back up my claim that there are two bars in NGC 1365:





And I can see the bars of NGC 1365.

Ann

Is there even a definition of a "bar" based on something other than mere appearance? Is it simply dust/gas that is apparently concentrated more or less predominantly along a line through the galaxy core?

I think it's purely a subjective, visual definition. In a sense, we might argue there is no such thing as a barred or unbarred spiral, merely a continuum between very strong and very weak central resonance structures... states that spiral galaxies appear to oscillate between over billions of years.

What's a "central resonance structure"?

[Chris Peterson]

Is there even a definition of a "bar" based on something other than mere appearance? Is it simply dust/gas that is apparently concentrated more or less predominantly along a line through the galaxy core?

I think it's purely a subjective, visual definition. In a sense, we might argue there is no such thing as a barred or unbarred spiral, merely a continuum between very strong and very weak central resonance structures... states that spiral galaxies appear to oscillate between over billions of years.

What's a "central resonance structure"?

Well, a bar is the most obvious one!

[AVAO]

Still not much of a definitive bar in M61 at all compared to your other examples. And I'm not convinced of the "inner" bar in NGC 1365 either!

"A bar is in the eye of the beholder" it seems.

I just told you that I don't necessarily always trust Wikipedia, but now I'm going to quote Wikipedia anyway to back up my claim that there are two bars in NGC 1365:

Wikipedia wrote:

NGC 1365 is a large barred spiral galaxy in the Fornax cluster. Within the larger long bar stretching across the center of the galaxy appears to be a smaller bar that comprises the core, with an apparent size of about 50″ × 40″.[3] This second bar is more prominent in infrared images of the central region of the galaxy, and likely arises from a combination of dynamical instabilities of stellar orbits in the region, along with gravity, density waves, and the overall rotation of the disc. The inner bar structure likely rotates as a whole more rapidly than the larger long bar, creating the diagonal shape seen in images.

And I can see the bars of NGC 1365.

Ann

Is there even a definition of a "bar" based on something other than mere appearance? Is it simply dust/gas that is apparently concentrated more or less predominantly along a line through the galaxy core?

Well. When I look at the galaxy in IR, it doesn't remind me much of a bar either.

...more like an alien....


Image source: SST

Image source: SST/JWST

Image source: SST/JWST

Image source: JWST/HST

Image source: HST

jac berne (flickr)
https://www.flickr.com/photos/185130090@N02/
[/quote]

[johnnydeep]

I just told you that I don't necessarily always trust Wikipedia, but now I'm going to quote Wikipedia anyway to back up my claim that there are two bars in NGC 1365:





And I can see the bars of NGC 1365.

Ann

Is there even a definition of a "bar" based on something other than mere appearance? Is it simply dust/gas that is apparently concentrated more or less predominantly along a line through the galaxy core?

Well. When I look at the galaxy in IR, it doesn't remind me much of a bar either.

...more like an alien....


Image source: SST
...

Image source: HST

jac berne (flickr)
https://www.flickr.com/photos/185130090@N02/

[/quote]

Not sure where the alien is, but it's remarkable how that last image is really only a very small part if the center! (or else I'm hopelessly confused - these are all pics of M61, right?)

[VictorBorun]

I just told you that I don't necessarily always trust Wikipedia, but now I'm going to quote Wikipedia anyway to back up my claim that there are two bars in NGC 1365:





And I can see the bars of NGC 1365.

Ann

Is there even a definition of a "bar" based on something other than mere appearance? Is it simply dust/gas that is apparently concentrated more or less predominantly along a line through the galaxy core?

Well. When I look at the galaxy in IR, it doesn't remind me much of a bar either.

...more like an alien....


Image source: SST

Image source: SST/JWST

Image source: SST/JWST

Image source: JWST/HST

Image source: HST

jac berne (flickr)
https://www.flickr.com/photos/185130090@N02/

[/quote]

I wish I knew if 3d shape of this face on grand design M100 is in fact planar

...

Click to view full size image 1 or image 2

[AVAO]

Is there even a definition of a "bar" based on something other than mere appearance? Is it simply dust/gas that is apparently concentrated more or less predominantly along a line through the galaxy core?

Well. When I look at the galaxy in IR, it doesn't remind me much of a bar either.

...more like an alien....


Image source: SST
...

Image source: HST

jac berne (flickr)
https://www.flickr.com/photos/185130090@N02/

"Intermediate" in this case means that the galaxy is midway between barred and unbarred galaxies. Take a look at this picture of the central part of M100:

Credit: Hubble Legacy Archive, NASA, ESA - Processing & Licence: Judy Schmidt

---

Note the two long, dark dust lanes winding their way from the very nucleus of M100 all the way out to the spiral arms. Such dust lanes are typical of barred galaxies. But the inner bulge of M100 is not elongated, as we would expect from a barred galaxy, and at least one of the spiral arms appears to begin almost at the nucleus.

Not sure where the alien is, but it's remarkable how that last image is really only a very small part if the center! (or else I'm hopelessly confused - these are all pics of M61, right?)

Uhhh, sorry. I was a little too sparing with explanations.
This is the same galaxy NGC 4321 (M100) as shown in the APOD.
You can see the "handle"-like hole relatively well to the left of center in my last close up picture.

[Guest]

Just getting around to all of the above responses. Thank you all for you Mr added insight into M100. Truly remarkable.

[johnnydeep]

Well. When I look at the galaxy in IR, it doesn't remind me much of a bar either.

...more like an alien....


Image source: SST
...

Image source: HST

jac berne (flickr)
https://www.flickr.com/photos/185130090@N02/

"Intermediate" in this case means that the galaxy is midway between barred and unbarred galaxies. Take a look at this picture of the central part of M100:

Credit: Hubble Legacy Archive, NASA, ESA - Processing & Licence: Judy Schmidt

---

Note the two long, dark dust lanes winding their way from the very nucleus of M100 all the way out to the spiral arms. Such dust lanes are typical of barred galaxies. But the inner bulge of M100 is not elongated, as we would expect from a barred galaxy, and at least one of the spiral arms appears to begin almost at the nucleus.

Not sure where the alien is, but it's remarkable how that last image is really only a very small part if the center! (or else I'm hopelessly confused - these are all pics of M61, right?)

Uhhh, sorry. I was a little too sparing with explanations.
This is the same galaxy NGC 4321 (M100) as shown in the APOD.
You can see the "handle"-like hole relatively well to the left of center in my last close up picture.

Thanks. I just wasn't seeing it! Confused I was indeed.

[DJE44]

Just getting around to all of the above responses. Thank you all for you for the added insight into M100. Truly remarkable.

-Drew

[Ann]

Okay, I'm finally ready to talk about today's splendid APOD, and I don't really know where to start. Let's start with an annotated version of the APOD!

APOD 2 May 2024 annotated.png

Majestic grand design galaxy M100 and friends.
Credit: Drew Evans.

M100 is surrounded by a lot of friends, or satellite galaxies. The two most important are NGC 4322 and NGC 4328. They are, in some ways, to M100 what the Magellanic Clouds are to the Milky Way:

The Milky Way and the Magellanic Clouds. Illustration: Nina McCurdy / Nick Risinger / NASA.

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If you ask me, NGC 4322 and NGC 4328 probably help shape the beautiful spiral arms of M100, and the Magellanic Clouds are possibly doing the same thing for our own galaxy. Of course, a huge difference is that the Magellanic Clouds are blue and pink from fresh star formation, whereas NGC 4322 and NGC 4328 are tired and yellow from geriatric stars only. NGC 4322 and NGC 4328 may have orbited M100 for a long time and thus lost their gas and their ability to form new stars, whereas the Magellanic Clouds have only recently been captured by the Milky Way, and they - or at least the LMC - is going to collide with our galaxy!!! Yikes!!!

Sci News wrote:

The Large Magellanic Cloud, a dwarf galaxy located approximately 163,000 light-years away, is on a collision course with the Milky Way with which it will merge in about 2.4 billion years, according to new research. This catastrophic event could wake up our Galaxy’s dormant supermassive black hole, which would begin devouring surrounding gas and increase in size by up to 8 times; the Milky Way’s stellar halo will undergo an equally impressive transformation, becoming 5 times more massive; the merger will also gravitationally eject central disk stars into the halo.

I don't know what plans NGC 4322 has for M100, but it is sitting inside the outer halo of M100, looking innocent and nucleated! (That is, it has a nucleus.)

NGC 4322. It is apparently sometimes called NGC 4323. Note the halo of M100 at lower right, and NGC 4322 is connected to it. Credit: SDSS.

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So let's talk about M100 itself, shall we?

The core of M100 is brilliant from a great starburst:

M100 is somewhat faint overall, but its core is brilliant from an ongoing starburst. Credit: ING Archive and Nik Szymanek.

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The inner disk of M100 is yellow from old stars, but its two majestic arms are blue. The inner arms shine from a mixture of blue star clusters and pink emission nebulas. But the spiral structure continues even after the blue arms end, now as broad spiral arms made of old, yellowish-beige stars. I guess you could say that the halo of M100 is spiral-shaped!

And did you know that a really titanic supernova exploded in M100 in 1979, SN 1979C? It is so important that it has its own Wikipedia entry:

A stellar-mass black hole. Credit: NASA/ESA

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Wikipedia wrote:

The Type II supernova was discovered April 19, 1979 by Gus Johnson, a school teacher and amateur astronomer...

The star that resulted in this supernova was estimated to be in the range of 20 solar masses...

On November 15, 2010 NASA announced that evidence of a black hole had been detected as a remnant of the supernova explosion. Scientists led by Dr. Dan Patnaude from the Center for Astrophysics | Harvard & Smithsonian in Cambridge, MA evaluated data gathered between 1995 and 2007 from several space based observatories. NASA's Chandra X-ray Observatory, the Swift Gamma-Ray Burst Mission, as well as the European Space Agency's XMM-Newton, and Germany's ROSAT all participated in the examination.

Okay, so it could be that the remnant is not a black hole but "only" a pulsar wind nebula from a rapidly spinning pulsar, similar to the Crab Nebula.

Whatever! This supernova was bright, by far the brightest that has been observed in M100. But so very little is known about it, because no one - and I mean no one - photographed it back in 1979! No one except James D Wray, who casually snapped a picture of it as he was photographing M100 for his atlas of galaxies!

Location of SN 1979C. The supernova remnant is visible in X-rays. Credit: X-ray: NASA/CXC/SAO/D.Patnaude et al, Optical: ESO/VLT, Infrared: NASA/JPL/Caltech

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The only picture ever of SN 1979C
from James D Wray's atlas!

Finally, M100 is a galaxy rich in star formation, yet it is a member of the large and rich Virgo Cluster. This would not be possible unless M100 was located on the outskirts of the Virgo Cluster - and it is!

M61, located very far away from the hue and cry of the other Virgo Cluster galaxies, is bursting with star formation. But that's a story for another day. Credit: ESA/Hubble & NASA, ESO, J. Lee and the PHANGS-HST Team

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The picture at left shows the Virgo Cluster. M100 is at the very top, whereas starburst galaxy M61 is far below the others. Both M100 and M61 are sufficiently far away from the crowded parts of the Virgo Cluster to be able to form a lot of stars.

I was not allowed to copy this image, and it disappeared from my previous post. So I uploaded it to my computer, and I'm re-posting it as an attachment. The picture is by SkySafari Astronomy.

Ann