APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

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APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by APOD Robot » Fri Jan 20, 2023 5:07 am

Image Galaxy Wars: M81 and M82

Explanation: The two dominant galaxies near center are far far away, 12 million light-years distant toward the northern constellation of the Great Bear. On the right, with grand spiral arms and bright yellow core is spiral galaxy M81. Also known as Bode's galaxy, M81 spans some 100,000 light-years. On the left is cigar-shaped irregular galaxy M82. The pair have been locked in gravitational combat for a billion years. Gravity from each galaxy has profoundly affected the other during a series of cosmic close encounters. Their last go-round lasted about 100 million years and likely raised density waves rippling around M81, resulting in the richness of M81's spiral arms. M82 was left with violent star forming regions and colliding gas clouds so energetic that the galaxy glows in X-rays. In the next few billion years, their continuing gravitational encounters will result in a merger, and a single galaxy will remain. This extragalactic scenario also includes other members of the interacting M81 galaxy group with NGC 3077 below and right of the large spiral, and NGC 2976 at upper right in the frame. Captured under dark night skies in the Austrian Alps, the foreground of the wide-field image is filled with integrated flux nebulae. Those faint, dusty interstellar clouds reflect starlight above the plane of our own Milky Way galaxy.

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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by Knight of Clear Skies » Fri Jan 20, 2023 10:47 am

There is an interesting image on this page with hydrogen-line radio data added, which shows the gas bridge between these galaxies:

https://theastroenthusiast.com/the-inte ... ic-cirrus/
Last edited by bystander on Sat Jan 21, 2023 5:01 am, edited 1 time in total.
Reason: fixed url
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Ann
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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by Ann » Fri Jan 20, 2023 11:39 am

Knight of Clear Skies wrote: Fri Jan 20, 2023 10:47 am There is an interesting image on this page with hydrogen-line radio data added, which shows the gas bridge between these galaxies:

https://theastroenthusiast.com/the-inte ... ic-cirrus/
Indeed, M81, M82 and NGC 3077 are interacting.


Both M82 and NGC 3077 are undergoing nuclear starbursts, while at the same time they are losing the gas in their disks. It could be that the gas and dust of M82 and NGC 3077 are flowing in two directions: one, into the core of the galaxies where they fuel starbursts, and two, out of the galaxies and into the bridge connecting M81, M82 and NGC 3077.

A nuclear starburst in M82.png
A nuclear starburst in M82.
The rest of the galaxy is "red and dead".

Fascinatingly, the fourth galaxy seen in the APOD (at upper right), NGC 2976, may just possibly also be affected by the violent interactions between M81, M82 and NGC 3077. Because NGC 2976 also looks a little "weird":


So it would seem that what is going on inside the M81 group is similar to what is going on inside much larger groups of galaxies: The galaxies lose gas and transform into elliptical or lenticular galaxies with no star formation.


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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by AVAO » Fri Jan 20, 2023 11:51 am

Knight of Clear Skies wrote: Fri Jan 20, 2023 10:47 am There is an interesting image on this page with hydrogen-line radio data added, which shows the gas bridge between these galaxies:
https://theastroenthusiast.com/the-inte ... tic-cirrus
The image source is a bit large due to the amount of data:
https://live.staticflickr.com/65535/522 ... 41af_o.png

But the article is very interesting:
https://theastroenthusiast.com/the-inte ... tic-cirrus
Interesting Features: Overlay: "Below is a comparison of an inverted luminance image to show the cirrus surrrounding these galaxies (black and white) and VLA’s HI emission obervations (red)."

see also the original website:
https://www.astron.nl/~blok/M81data

Image
HI data of the M81 Triplet (M81, M82, NGC3077) de Blok et al. 2018

See also previous discussions:
viewtopic.php?t=40564
viewtopic.php?t=35615
Last edited by AVAO on Fri Jan 20, 2023 8:24 pm, edited 1 time in total.

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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by orin stepanek » Fri Jan 20, 2023 3:07 pm

The title reminds me me of the Tv series Star Wars Galactica! :shock:
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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by Fred the Cat » Fri Jan 20, 2023 4:44 pm

Are density waves a proven theory? To me, they sound as nebulous as dark matter. :?
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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by Chris Peterson » Fri Jan 20, 2023 5:48 pm

Fred the Cat wrote: Fri Jan 20, 2023 4:44 pm Are density waves a proven theory? To me, they sound as nebulous as dark matter. :?
There is no such thing as a proven theory. They cannot ever be proven, only disproven. Density wave theory is very widely accepted because it is modellable and the output of the models closely match observation.
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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by AVAO » Fri Jan 20, 2023 6:36 pm

.
How to explain that Holmberg IX is almost invisible on today's APOD?
Compare to: https://live.staticflickr.com/65535/522 ... 9cb7_o.png
How did it form and is there still star formation there?

Image
UV / GALEX (https://upload.wikimedia.org/wikipedia/ ... alex_f.jpg)
Last edited by AVAO on Fri Jan 20, 2023 7:50 pm, edited 1 time in total.

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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by Fred the Cat » Fri Jan 20, 2023 7:11 pm

Chris Peterson wrote: Fri Jan 20, 2023 5:48 pm
Fred the Cat wrote: Fri Jan 20, 2023 4:44 pm Are density waves a proven theory? To me, they sound as nebulous as dark matter. :?
There is no such thing as a proven theory. They cannot ever be proven, only disproven. Density wave theory is very widely accepted because it is modellable and the output of the models closely match observation.
Thanks! Modeling is good. Searching further about both topics, Hubert Bray published an article about wave dark matter that discussed 3D modeling of galaxies. I found it interesting that scalar field models may be bosonic.

You know me; a scalar field model expert. :no:
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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by johnnydeep » Fri Jan 20, 2023 7:53 pm

Knight of Clear Skies wrote: Fri Jan 20, 2023 10:47 am There is an interesting image on this page with hydrogen-line radio data added, which shows the gas bridge between these galaxies:

https://theastroenthusiast.com/the-inte ... ic-cirrus/
I guess it's only me, but it's only when I reply to this post that I see the link that's obviously within it. <sigh>

Let me add the exact same url tag here and see what happens:

https://theastroenthusiast.com/the-inte ... ic-cirrus/

Ah, it's because there's no display text specified between the tags!
Last edited by bystander on Sat Jan 21, 2023 5:00 am, edited 1 time in total.
Reason: fixed url
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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by Ann » Fri Jan 20, 2023 8:23 pm

AVAO wrote: Fri Jan 20, 2023 6:36 pm .
How to explain that Holmberg IX is almost invisible on today's APOD?
Compare to: https://live.staticflickr.com/65535/522 ... 9cb7_o.png
How did it form and is there still star formation there?

Image
UV / GALEX (https://upload.wikimedia.org/wikipedia/ ... alex_f.jpg)
Holmberg IX has a low surface brightness in optical and infrared light. It is only bright in the ultraviolet. In optical light, it is much fainter than the bluish spiral arms of M81. But I disagree that this little galaxy is invisible in today's APOD. It is plainly there, below M81, in the 7 o'clock position.

How did Holmberg IX form? Most likely, if you ask me, a chunk of gas that was thrown out from M81 during its interactions with M82 and NGC 3077 was jostled so that the gas got sufficiently compressed that it started forming stars.

This is pretty basic stuff, really. We see the same kind of dwarf galaxy formation in the tidal tail of the Tadpole galaxy and in the tail of NGC 4038 of the Antennae galaxies. Admittedly, in the case of M81 we don't see a tidal tail, but we do see bridges of neutral gas between M81, M82 and NGC 3077.


I'd say it's the same thing going on with Holmberg IX.

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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by AVAO » Fri Jan 20, 2023 9:04 pm

Ann wrote: Fri Jan 20, 2023 8:23 pm
AVAO wrote: Fri Jan 20, 2023 6:36 pm .
How to explain that Holmberg IX is almost invisible on today's APOD?
Compare to: https://live.staticflickr.com/65535/522 ... 9cb7_o.png
Holmberg IX has a low surface brightness in optical and infrared light. It is only bright in the ultraviolet. In optical light, it is much fainter than the bluish spiral arms of M81. But I disagree that this little galaxy is invisible in today's APOD. It is plainly there, below M81, in the 7 o'clock position.
...

Ann
Sorry Ann, but I don't agree with that either. The image has a relatively poor resolution and the galaxies shown are severely distorted on closer look. Holmberg IX is a nebula with no single star visible and no hint of blue for reference.

For me, however, some things become clear when I follow the author's original text on instagram. In honor of - that photographers, who define themselves as "beginners", are also making it onto the APOD throne. Congratulations.

"The real highlight in this image, however, is the integrated flux nebula (IFN, the faint nebulosity all over the image). This nebula lies beyond the main body of the Milky Way. It is a component of the interstellar medium, composed of dust particles, hydrogen and other elements. It is illuminated by the energy from the integrated flux of all the stars in our galaxy (hence it’s name). It is extremely difficult to shoot, as it requires very dark skies, long integration time and careful processing. Thus, I’m very satisfied that I could capture it as a beginner in my first attempt!"

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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by AVAO » Fri Jan 20, 2023 9:44 pm

Ann wrote: Fri Jan 20, 2023 8:23 pm
AVAO wrote: Fri Jan 20, 2023 6:36 pm How did it form and is there still star formation there?
How did Holmberg IX form? Most likely, if you ask me, a chunk of gas that was thrown out from M81 during its interactions with M82 and NGC 3077 was jostled so that the gas got sufficiently compressed that it started forming stars.

This is pretty basic stuff, really. We see the same kind of dwarf galaxy formation in the tidal tail of the Tadpole galaxy and in the tail of NGC 4038 of the Antennae galaxies. Admittedly, in the case of M81 we don't see a tidal tail, but we do see bridges of neutral gas between M81, M82 and NGC 3077.

I'd say it's the same thing going on with Holmberg IX.

Ann
ThanX Ann for your detailed explanations.

Wikipedia says: "Holmberg IX is a dwarf irregular galaxy and a satellite galaxy of M81...Based on the observed age distribution of stars it contains it is thought to have formed within the last 200 Myr making it the youngest nearby galaxy."

It seems that until recently there was a lot going on in the area.

... and I like blue blobs :brr: too...

Image
https://esahubble.org/images/heic0801a/

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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by Ann » Sat Jan 21, 2023 5:57 am

AVAO wrote: Fri Jan 20, 2023 9:04 pm
Ann wrote: Fri Jan 20, 2023 8:23 pm
AVAO wrote: Fri Jan 20, 2023 6:36 pm .
How to explain that Holmberg IX is almost invisible on today's APOD?
Compare to: https://live.staticflickr.com/65535/522 ... 9cb7_o.png
Holmberg IX has a low surface brightness in optical and infrared light. It is only bright in the ultraviolet. In optical light, it is much fainter than the bluish spiral arms of M81. But I disagree that this little galaxy is invisible in today's APOD. It is plainly there, below M81, in the 7 o'clock position.
...

Ann
Sorry Ann, but I don't agree with that either. The image has a relatively poor resolution and the galaxies shown are severely distorted on closer look. Holmberg IX is a nebula with no single star visible and no hint of blue for reference.
I guess we may have to agree to disagree, then. Because I insist that Holmberg IX is faint, and it doesn't show up well at all in many images. See here:

Barely any Holmberg IX here. Barely any Holmberg IX here.

And I highly recommend this gallery of a whole bunch of M81 pictures where Holmberg IX is either just barely there, or else completely absent altogether.

Perhaps you are saying that we should ask more of an M81/M82 portrait that gets chosen to be an APOD. Yes, maybe so. I like the image as it is, though, and since it is not trying to show us Holmberg IX specifically, I think that even the wisp of Holmberg IX looks good enough.

To me, the faintness of Holmberg IX in the APOD is a counterpart to the complete lack of red color in M82 in the APOD. Or to put it differently:

Some things in space are not so visible, and you have to work hard to make them visible. But seeing these objects the way they look without all that extra processing and filters to bring them out is also interesting.

The APOD did a good job at bringing out small dwarf galaxies:

APOD 20 January 2023 annotated.png

Ann
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Re: APOD: Galaxy Wars: M81 and M82 (2023 Jan 20)

Post by AVAO » Sat Jan 21, 2023 7:56 am

Ann wrote: Sat Jan 21, 2023 5:57 am
AVAO wrote: Fri Jan 20, 2023 9:04 pm
Ann wrote: Fri Jan 20, 2023 8:23 pm

Holmberg IX has a low surface brightness in optical and infrared light. It is only bright in the ultraviolet. In optical light, it is much fainter than the bluish spiral arms of M81. But I disagree that this little galaxy is invisible in today's APOD. It is plainly there, below M81, in the 7 o'clock position.
...

Ann
Sorry Ann, but I don't agree with that either. The image has a relatively poor resolution and the galaxies shown are severely distorted on closer look. Holmberg IX is a nebula with no single star visible and no hint of blue for reference.
I guess we may have to agree to disagree, then. Because I insist that Holmberg IX is faint, and it doesn't show up well at all in many images. See here:

Barely any Holmberg IX here. Barely any Holmberg IX here.

And I highly recommend this gallery of a whole bunch of M81 pictures where Holmberg IX is either just barely there, or else completely absent altogether.

Perhaps you are saying that we should ask more of an M81/M82 portrait that gets chosen to be an APOD. Yes, maybe so. I like the image as it is, though, and since it is not trying to show us Holmberg IX specifically, I think that even the wisp of Holmberg IX looks good enough.

To me, the faintness of Holmberg IX in the APOD is a counterpart to the complete lack of red color in M82 in the APOD. Or to put it differently:

Some things in space are not so visible, and you have to work hard to make them visible. But seeing these objects the way they look without all that extra processing and filters to bring them out is also interesting.

The APOD did a good job at bringing out small dwarf galaxies:


APOD 20 January 2023 annotated.png


Ann
ThanX Ann

I asked why Holmberg IX isn't more visible. This especially in comparison to the main arm of M81 lying next to it. If I follow your link to the image gallery and compare, I learn that it is apparently not easy for astrophotographers with their own equipment to image Holmberg IX in such a way that individual star clusters or bright individual stars are also visible. That answers my question.

On the other hand, I find your argumentation very good because it refers to how a picture should be read and appreciated. When I read the image author's own text, he was concerned with two things: faintly visible background galaxies and the flux nebulae from our own galaxy. The fact that only an old standard text was used for the APOD is unfortunately misleading. Here it would be desirable if the APOD text authors could also respond a little more to the individual intentions of the image authors in the future. Perhaps a combination of existing and new aspects would be best here. But of course I also find it enormously important and valuable that the APOD and this blog is managed here without a commercial background. This trade off remains.