Starship Asterisk*

Massive Nearby Spiral Galaxy NGC 2841

Explanation: It is one of the more massive galaxies known. A mere 46 million light-years distant, spiral galaxy NGC 2841 can be found in the northern constellation of Ursa Major. This sharp view of the gorgeous island universe shows off a striking yellow nucleus and galactic disk. Dust lanes, small, pink star-forming regions, and young blue 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 and captured by this composite image merging exposures from the orbiting 2.4-meter Hubble Space Telescope and the ground-based 8.2-meter Subaru Telescope. X-ray images suggest that resulting winds and stellar explosions create plumes of hot gas extending into a halo around NGC 2841.

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Very very interesting

I'm very glad to see a gorgeous spiral galaxy here!

NGC 2841 is indeed a fascinating galaxy. It is a so called flocculent galaxy, which means that it doesn't have any long sweeping arms, but instead a patchy disk displaying an overall spiral structure. The kind of star formation seen in NGC 2841, which occurs at rather random spots in the disk, is called stochastic star formation.

It is clear that NGC 2841 has not undergone any sort of major star formation, let alone any major mergers, recently. Look how regular and "settled" it looks! Compare its appearance with some of the big star formation-chaotic spiral galaxies like, say, M101.

Note the neat fact that the dust lanes closest to the yellow bulge look bluer on the far side than on the near side. That is because the dust on the far side is scattering the (slightly bluish) star light our way, like a blue reflection nebula. But on the near side, the dust is blocking the blue star light, causing a reddening effect.

Ann

I do wonder why this one is considered a spiral while the Sombrero is considered to be a lenticular galaxy.

What is the small black dot in the left part of the bulge? It looks round and not an artifact.

Hello,

What is the black spot near the center of the picture ?

Best regards

geckzilla wrote:I do wonder why this one is considered a spiral while the Sombrero is considered to be a lenticular galaxy.

Is it really? I have seen a classification of Sa-b for the Sombrero. M104 looks like a dead giveaway Sa spiral to me!

But there are differences between NGC 2841 and M104. I think M104 appears to have a larger bulge and a much fatter halo than NGC 2841, for example. Also, I think that M104 seems to lack ongoing star formation altogether. At the very least, no existing image of M104 shows emission nebulas or obvious young blue clusters, as far as I'm aware.

Of course, the lack of star formation doesn't prevent a spiral galaxy from being a spiral galaxy, that's for sure.

Ann

P.S. Has anyone noted that NGC 2841 appears to be a perfect spiral for today's date? In some languages, April the 28th can be pronounced as 28-4. Now we just need to find out where the number one came from...

Anyone know what the two faint streaks are on the right? I'm guessing passing satellites?

geckzilla wrote:I do wonder why this one is considered a spiral while the Sombrero is considered to be a lenticular galaxy.

The Sombrero is a spiral galaxy. Where have you seen it classified as a lenticular?

> NGC 2841 has a diameter of over 150,000 light-years,
But how massive is it? With all the talk about dark matter, one could get the impression, that there is a good understanding of how much mass is distributed in the bright matter.

Chris Peterson wrote:

geckzilla wrote:
I do wonder why this one is considered a spiral while the Sombrero is considered to be a lenticular galaxy.

The Sombrero is a spiral galaxy. Where have you seen it classified as a lenticular?

Brian Koberlein calls the Sombrero galaxy "a fascinating lenticular."

Sky Vistas calls the Sombrero galaxy a classic example of "a transitional SO/a" lenticular/spiral.

M104 classified as type SA(s)a.
See: http://ned.ipac.caltech.edu/cgi-bin/nph ... _stamp=YES

Which seems to make sense. Except for the dust lanes the Sombrero galaxy is kinda 'fat'.

slater wrote:Anyone know what the two faint streaks are on the right? I'm guessing passing satellites?

Not sure what it is. The long one is rather prominent.
Doubtful it is due to satellites though. Images like this sometimes take hours to collect enough light. Any satellite would have passed right through. Besides, Hubble is too high for most satellites anyway. Probably just an image or processing artifact.

Craine wrote:

slater wrote:Anyone know what the two faint streaks are on the right? I'm guessing passing satellites?

Not sure what it is. The long one is rather prominent.
Doubtful it is due to satellites though. Images like this sometimes take hours to collect enough light. Any satellite would have passed right through. Besides, Hubble is too high for most satellites anyway. Probably just an image or processing artifact.

It's a composite of Hubble and Subaru telescope images, so I'm thinking it might be possible...?

slater wrote:

Craine wrote:

slater wrote:Anyone know what the two faint streaks are on the right? I'm guessing passing satellites?

Not sure what it is. The long one is rather prominent.
Doubtful it is due to satellites though. Images like this sometimes take hours to collect enough light. Any satellite would have passed right through. Besides, Hubble is too high for most satellites anyway. Probably just an image or processing artifact.

It's a composite of Hubble and Subaru telescope images, so I'm thinking it might be possible...?

We may never know. But look at the just to the left of where the long streak ends. You'll see a 'fuzzy' area with clear sings of image processing. My guess would be that is the area where multiple images were stitched together and didn't quite fit right. You can always ask the author: Roberto Colombari.

neufer wrote:

Chris Peterson wrote:

geckzilla wrote:
I do wonder why this one is considered a spiral while the Sombrero is considered to be a lenticular galaxy.

The Sombrero is a spiral galaxy. Where have you seen it classified as a lenticular?

Brian Koberlein calls the Sombrero galaxy "a fascinating lenticular."

Sky Vistas calls the Sombrero galaxy a classic example of "a transitional SO/a" lenticular/spiral.

You may have noticed my three confused posts at that link to Brian's blog. It's possible it is not one of his finest entries. Transitional is probably a very good description for Sombrero.

Craine wrote:

slater wrote:

Craine wrote: Not sure what it is. The long one is rather prominent.
Doubtful it is due to satellites though. Images like this sometimes take hours to collect enough light. Any satellite would have passed right through. Besides, Hubble is too high for most satellites anyway. Probably just an image or processing artifact.

It's a composite of Hubble and Subaru telescope images, so I'm thinking it might be possible...?

We may never know. But look at the just to the left of where the long streak ends. You'll see a 'fuzzy' area with clear sings of image processing. My guess would be that is the area where multiple images were stitched together and didn't quite fit right. You can always ask the author: Roberto Colombari.

This happens almost every time one of Roberto's images is run. He doesn't clean up all of the dirt and artifacts as well as he could.

Mark Bosley wrote:What is the small black dot in the left part of the bulge? It looks round and not an artifact.

Patrick Fave wrote:Hello,

What is the black spot near the center of the picture ?

Best regards

Not certain though there are numerous more black splotches in the area surrounding the brightest star in the image in the lower left

geckzilla wrote:
This happens almost every time one of Roberto's images is run. He doesn't clean up all of the dirt and artifacts as well as he could.

[Joking mode on]
Also my wife always complains I leave dirty stuff all around the house everyday
Next time I'll try to clean it up better
[Joking mode off]

It is an artifact, yes! Most probably a satellite on the Subaru frames

neufer wrote:

Chris Peterson wrote:

geckzilla wrote:
I do wonder why this one is considered a spiral while the Sombrero is considered to be a lenticular galaxy.

The Sombrero is a spiral galaxy. Where have you seen it classified as a lenticular?

Brian Koberlein calls the Sombrero galaxy "a fascinating lenticular."

Sky Vistas calls the Sombrero galaxy a classic example of "a transitional SO/a" lenticular/spiral.

Thanks, Art, for the info.

Personally I have never heard of Brian Koberlein. And while I have heard of Sky Vistas, that site is not where I would automatically go to check up an astronomical fact (or a piece of opinion about something astronomical). That doesn't mean that the opinion of these two sources is unimportant, to be sure.

To me, Simbad Astronomical Database seems more important. (The rest of you may disagree.) Simbad wrote about M104:

Spectral type: S0//Sa D
Morphological type: Sa D

I find this interesting. S0 galaxies are typically devoid of star formation, and the type of stars that M104 contains makes it rather similar to an S0 galaxy. But morphologically, when it comes to its shape, it is an Sa galaxy.

I probably shouldn't confess my ignorance when I've just recommended Simbad as a source of astronomical knowledge, but... does anyone know what the "D" stands for in S0// Sa D and Sa D?

Ann

Geckzilla wrote:
This happens almost every time one of Roberto's images is run. He doesn't clean up all of the dirt and artifacts as well as he could.

This may well be true. For me personally, however, who look at the overall impression of the image and at details that obviously aren't artifacts, your images are a joy to look at, Roberto.

Ann

rcolombari wrote:

geckzilla wrote:
This happens almost every time one of Roberto's images is run. He doesn't clean up all of the dirt and artifacts as well as he could.

[Joking mode on]
Also my wife always complains I leave dirty stuff all around the house everyday
Next time I'll try to clean it up better
[Joking mode off]

It is an artifact, yes! Most probably a satellite on the Subaru frames

Well then, Mark was right!

Ann wrote:

Geckzilla wrote:
This happens almost every time one of Roberto's images is run. He doesn't clean up all of the dirt and artifacts as well as he could.

This may well be true. For me personally, however, who look at the overall impression of the image and at details that obviously aren't artifacts, your images are a joy to look at, Roberto.

Ann

Thanks a lot Ann; indeed, I also understand Judy's point of view.
The problem is that it is not always easy and far from being trivial to remove all that isn't true signal!
For instance, for colorizing this image (= creating the RGB) I have chosen a different approach from many other compositions I did trying to use just DSS, Subaru and HST frequencies and avoid amateur observations.
This resulted in an increased complexity which lead to some error during the creation.

Craine wrote:

rcolombari wrote:

geckzilla wrote:
This happens almost every time one of Roberto's images is run. He doesn't clean up all of the dirt and artifacts as well as he could.

[Joking mode on]
Also my wife always complains I leave dirty stuff all around the house everyday
Next time I'll try to clean it up better
[Joking mode off]

It is an artifact, yes! Most probably a satellite on the Subaru frames

Well then, Mark was right!

Don't take my info as 100% correct, please; I have to take a look at the frames and probably to some intermediate processing step to give the correct answer.

Bests
Roberto

rcolombari wrote:[Joking mode on]
Also my wife always complains I leave dirty stuff all around the house everyday
Next time I'll try to clean it up better
[Joking mode off]

I nag you so many times and you still don't do it.