APOD: Spiral Galaxy NGC 2841 (2022 Mar 03)

[APOD Robot]

Spiral Galaxy NGC 2841

Explanation: A mere 46 million light-years distant, spiral galaxy NGC 2841 can be found in the northern constellation of Ursa Major. This deep view of the gorgeous island universe was captured during 32 clear nights in November, December 2021 and January 2022. It shows off a striking yellow nucleus, galactic disk, and faint outer regions. Dust lanes, small star-forming regions, and young star clusters are embedded in the patchy, tightly wound spiral arms. In contrast, many other spirals exhibit grand, sweeping arms with large star-forming regions. NGC 2841 has a diameter of over 150,000 light-years, even larger than our own Milky Way. X-ray images suggest that resulting winds and stellar explosions create plumes of hot gas extending into a halo around NGC 2841.

<< Previous APOD

This Day in APOD

Next APOD >>

[orin stepanek]

NGC2841_20220114_72H_1024.jpg

APOD tightly wound spiral arms.

The arms ARE tightly wound! Does that indicate that this a young or
old galaxy or just a fluke of how it formed?
It is a beautiful galaxy; as most galaxies are!

[Stargeezer2233]

Given the almost complete lack of pink or blue regions, is NGC 2841 really old?

[bystander]

Given the almost complete lack of pink or blue regions, is NGC 2841 really old?

I think that's just processing. For contrast, see this ESA Hubble image from 2011.

Credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration Acknowledgment: M. Crockett and S. Kaviraj (Oxford University, UK), R. O'Connell (University of Virginia), B. Whitmore (STScI) and the WFC3 Scientific Oversight Committee.

---

Or search APOD for NGC 2841

[Ann]

Spiral Galaxy NGC 2841. Image Credit & Copyright: Vitali Pelenjow.

---

APOD March 3 2022 NGC 2841 annotated.png

Today's APOD is a very fine picture acquired with an amateur telescope! I particularly like the portrait of NGC 2841's outer regions. For a galaxy with such a regular and symmetrical dust disk, the outer regions are interestingly "disturbed". They also show clear signs of star formation.

Personally I'm intrigued by a blue-white foreground star masquerading(?) as a supernova.It sure looks like a supernova to me. Compare it with the blue-white supernova SN 2020jfo in M61:

Supernova in M66 TheVastReaches.png

"Before" and "After" images of M61 with Supernova 2020jfo (arrowed).
Photo: TheVastReaches.

Well, I'll bet the blue-white star in NGC 2841 is just a foreground star, because there is no way that everybody would have missed it if it had been a real supernova!

In today's APOD, also note the only pink emission nebula that is bright enough to show up in the image - and do note that Vitali Pelenjow did not use an Hα filter.

To get a good grip on what NGC 2841 looks like, we need to look at it(s central regions) in a Hubble image.It is also interesting to compare it with a very similar galaxy, NGC 2775:

Flocculent galaxy NGC 2841. Note the brightest pink emission nebula at far left, near 10 o'clock. Credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration Acknowledgment: M. Crockett and S. Kaviraj (Oxford University, UK), R. O'Connell (University of Virginia), B. Whitmore (STScI) and the WFC3 Scientific Oversight Committee.

---

Flocculent galaxy NGC 2775. Image credit: NASA / ESA / Hubble / J. Lee / PHANGS-HST Team / Judy Schmidt, www.geckzilla.com.

---

ESA/Hubble wrote regarding their image of NGC 2841:

Star formation is one of the most important processes in shaping the Universe; it plays a pivotal role in the evolution of galaxies and it is also in the earliest stages of star formation that planetary systems first appear.

Yet there is still much that astronomers don’t understand, such as how do the properties of stellar nurseries vary according to the composition and density of gas present, and what triggers star formation in the first place? The driving force behind star formation is particularly unclear for a type of galaxy called a flocculent spiral, such as NGC 2841 shown here, which features short spiral arms rather than prominent and well-defined galactic limbs.

But when it came to NGC 2775, astronomers seemed much more certain of what caused the galaxy's flocculent spiral arms:

NASA / ESA / Hubble wrote:

NGC 2275 has a diameter of 80,000 light-years and is classified as a flocculent spiral galaxy. “NGC 2775’s ‘flocculent’ spiral arms indicate that the recent history of star formation of the galaxy has been relatively quiet,” Hubble astronomers said. “There is virtually no star formation in the central part of the galaxy, which is dominated by an unusually large and relatively empty galactic bulge, where all the gas was converted into stars long ago.” “Millions of bright, young, blue stars shine in the complex, feather-like spiral arms, interlaced with dark lanes of dust,” they noted. “Complexes of these hot, blue stars are thought to trigger star formation in nearby gas clouds.” “The overall feather-like spiral patterns of the arms are then formed by shearing of the gas clouds as the galaxy rotates.” “The spiral nature of flocculents stands in contrast to the grand design spirals, which have prominent, well defined-spiral arms.”

Okay, I guess. ¯\_(ツ)_/¯

Ann

[AVAO]

Hi Ann

Personally I'm intrigued by a blue-white foreground star masquerading(?) as a supernova.It sure looks like a supernova to me.

Probably intuition. SN 1999by was right next to it
However, the star should effectively be a foreground star, since it was already visible in 1999.


Color image of SN 1999by in NGC 2841. Photo: UCB

[AVAO]

Source: Jac Berne, flickr

Nice core ...

[Ann]

Given the almost complete lack of pink or blue regions, is NGC 2841 really old?

Practically all galaxies are old. The bluest known galaxy in nearby space, I Zwicky 18, is old.

I Zwicky 18. Credit: HST/NASA/ESA

---

Wikipedia wrote about I Zwicky 18:

Studies at the Palomar Observatory some 40 years ago led astronomers to believe that the galaxy erupted with star formation billions of years after its galactic neighbours. Galaxies resembling I Zwicky 18's youthful appearance are typically found only in the early universe. Early observations with the Hubble Space Telescope suggested an age of 500 million years old for I Zwicky 18...

Later observations with the Hubble Space Telescope found faint and old stars contained within the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as ten billion years ago. The galaxy, therefore, may have formed at the same time as most other galaxies.

The question is whether or not galaxies run out of gas and stop forming stars. NGC 2841 appears to have relatively little gas. More importantly, perhaps, NGC 2841 seems to be inefficient at converting its gas into stars. This galaxy is an underachiever at star formation.

My impression is that flocculent galaxies - galaxies that lack long elegant spiral arms, and instead have a multitude of small armlets like NGC 2841 - don't form stars very efficiently. They definitely seem to be poor in large flamboyant pink emission nebulas and blue star clusters.

Why is that? And how did the flocculent galaxies become flocculent?

Beats me.

Ann

[Ann]

Source: Jac Berne, flickr

Nice core ...

Nice core indeed. The galaxy seems completely unbarred. I wonder, could it be a signature feature of flocculent galaxies that they lack bars? Because flocculent galaxy NGC 2775 doesn't have a bar, either. And NGC 4414 doesn't, either. And M63 doesn't.

Ann

[Fred the Cat]

My computer doesn’t respond to the link for Vitali’s image credit but another of his astrophotographs aligns quite nicely.

[orin stepanek]

Given the almost complete lack of pink or blue regions, is NGC 2841 really old?

1929902587_LTNGC2841RGB(PI)PS62sign.jpg.d822d0bbdb3b9ef7e5e8165124f2dec6.jpg

Here it is with some blue!

[johnnydeep]

Ann wrote above:

In today's APOD, also note the only pink emission nebula that is bright enough to show up in the image - and do note that Vitali Pelenjow did not use an Hα filter.

But in looking at the pic where she points it out, I have to admit to seeing nothing special about that area compared to any others. Here's a close-up:

ngc 2841 ann-otations.JPG

And not even in the higher resolution Hubble image (though the near side does look overall more pinkish than the far side!):

This image is a composite of separate exposures acquired by the WFC3 instrument on HST. Several filters were used to sample broad and narrow wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: Blue: F336W (U) Green: F547M (y) Red/orange: F657N (H-alpha + [N II]) Red: F814W (I)

---

[alter-ego]

Hi Ann

Personally I'm intrigued by a blue-white foreground star masquerading(?) as a supernova.It sure looks like a supernova to me.

Probably intuition. SN 1999by was right next to it
However, the star should effectively be a foreground star, since it was already visible in 1999.


Color image of SN 1999by in NGC 2841. Photo: UCB

Foreground star: GSC 03431-00495
M_B: 14.4
Distance: 900 pc ± 1.5%

[Ann]

Ann wrote above:

In today's APOD, also note the only pink emission nebula that is bright enough to show up in the image - and do note that Vitali Pelenjow did not use an Hα filter.

But in looking at the pic where she points it out, I have to admit to seeing nothing special about that area compared to any others. Here's a close-up:

Click to view full size image

And not even in the higher resolution Hubble image (though the near side does look overall more pinkish than the far side!):

This image is a composite of separate exposures acquired by the WFC3 instrument on HST. Several filters were used to sample broad and narrow wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: Blue: F336W (U) Green: F547M (y) Red/orange: F657N (H-alpha + [N II]) Red: F814W (I)

---

APOD March 5 2022 closeup NGC 2841.png

APOD March 5 2022 closeup NGC 2841 annotated.png

Hope you can see it now, Johnny. And if you still can't see it, click on the image with the arrows to enlarge it.

You wrote:

the near side does look overall more pinkish than the far side

I disagree. The near side looks more brownish than the far side, because the dust is more obvious and stands out more on the near side than on the far side. On the far side, by contrast, the tiny blue clusters stand out more.

Or else I'm wrong, and it is the other way round! Either way, the dust stands out more on one side and the tiny bluish star clusters stand out more on the other side. The effect must be caused by inclination and reddening or the lack of it, and perhaps reflection.

Ann

[johnnydeep]

Ok, Ann, maybe I can see the pink nebula in today's APOD now, but my convincing may be due more to the pink arrows you used to point it out than to any real pink nebula that is present

ngc 2841 close-up of pinkish nebula.JPG

However, I think I can also now see the same area in the much clearer Hubble pic, and clearly there is something different going on there:

ngc 2841 close-up of pinkish nebula in Hubble image.JPG

[johnnydeep]

And here's an even closer up view from the 11 MB jpeg here https://cdn.spacetelescope.org/archives ... c1104a.jpg

ngc 2841 closer-up of pinkish nebula in Hubble image.JPG

[Ann]

Ok, Ann, maybe I can see the pink nebula in today's APOD now, but my convincing may be due more to the pink arrows you used to point it out than to any real pink nebula that is present

Click to view full size image

Ann's pink nebula?

Exactly, Johnny, you found it!

However, I think I can also now see the same area in the much clearer Hubble pic, and clearly there is something different going on there:

Click to view full size image

Is this also Ann's Pink Nebula?

Exactly! It's the same nebula.

Ann

[Ann]

And here's an even closer up view from the 11 MB jpeg here https://cdn.spacetelescope.org/archives ... c1104a.jpg

Click to view full size image

Thanks, that's a good one!

That nebula may well be the largest and brightest emission nebula in the entire galaxy.

Ann

[johnnydeep]

And here's an even closer up view from the 11 MB jpeg here https://cdn.spacetelescope.org/archives ... c1104a.jpg

Click to view full size image

Thanks, that's a good one!

That nebula may well be the largest and brightest emission nebula in the entire galaxy.

Ann

I never would have spotted this in the APOD image, and I'm impressed you were able to.  Even more so because of your professed azurophilia! 

[Ann]

I never would have spotted this in the APOD image, and I'm impressed you were able to.  Even more so because of your professed azurophilia! 

Thanks, I love that word!

Ann

[johnnydeep]

I never would have spotted this in the APOD image, and I'm impressed you were able to.  Even more so because of your professed azurophilia! 

Thanks, I love that word!

Ann

I knew you would azurify it!

[Ann]

I never would have spotted this in the APOD image, and I'm impressed you were able to.  Even more so because of your professed azurophilia! 

Thanks, I love that word!

Ann

I knew you would azurify it!

And I did!

Ann