APOD: Grand Spiral Galaxy M81 and Arps Loop (2013 Apr 16)

[APOD Robot]

Grand Spiral Galaxy M81 and Arps Loop

Explanation: One of the brightest galaxies in planet Earth's sky is similar in size to our Milky Way Galaxy: big, beautiful M81. This grand spiral galaxy lies 11.8 million light-years away toward the northern constellation of the Great Bear (Ursa Major). The deep image of the region reveals details in the bright yellow core, but at the same time follows fainter features along the galaxy's gorgeous blue spiral arms and sweeping dust lanes. It also follows the expansive, arcing feature, known as Arp's loop, that seems to rise from the galaxy's disk at the upper right. Studied in the 1960s, Arp's loop has been thought to be a tidal tail, material pulled out of M81 by gravitational interaction with its large neighboring galaxy M82. But a subsequent investigation demonstrates that at least some of Arp's loop likely lies within our own galaxy. The loop's colors in visible and infrared light match the colors of pervasive clouds of dust, relatively unexplored galactic cirrus only a few hundred light-years above the plane of the Milky Way. Along with the Milky Way's stars, the dust clouds lie in the foreground of this remarkable view. M81's dwarf companion galaxy, Holmberg IX, can be seen just above the large spiral. On the sky, this image spans about 0.5 degrees, about the size of the Full Moon.

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[Ann]

This is a lovely image, and I'm so happy to see a galaxy here again. And what a beautiful galaxy it is! I agree that Arp's Loop doesn't look like a typical galaxy tidal tail, and therefore it is most likely a (smallish) part of our own galaxy. (I'm not arguing one way or another with those who have used scientific methods to prove that much of Arp's Loop is a Milky Way feature, I'm just saying that it looks that way to me!)

Ann

[alter-ego]

Grand Spiral Galaxy M81

Aside from being visually grand:

A grand design spiral galaxy is a type of spiral galaxy with prominent and well-defined spiral arms, as opposed to multi-arm and flocculent spirals which have subtler structural features. The spiral arms of a grand design galaxy extend clearly around the galaxy through many radians and can be observed over a large fraction of the galaxy's radius. Approximately 10 percent of spiral galaxies are classified as grand design type spirals,[1] including M81, M51 and M74.

[JonD]

Arp's Loop is part of the Milky Way?
The link isn't helpful, doesn't mention the Loop.

If M81 is 12M light years away, a hundred times further away than the furthest part of this galaxy, how can it be part of our galaxy?

JOhn

[geckzilla]

Arp's Loop is part of the Milky Way?
The link isn't helpful, doesn't mention the Loop.

If M81 is 12M light years away, a hundred times further away than the furthest part of this galaxy, how can it be part of our galaxy?

JOhn

If it's that far, then obviously it's not part of our galaxy. Reading the abstract here and from the APOD description, the confusion seems to be about whether or not the structure is dust in our galaxy or a trail of stars around that galaxy or a combination of both. Just looking at it it's hard to tell what's in the foreground and what's in the background.

[saturno2]

This Spiral Galaxy M81, is magnificent, beautiful

[Boomer12k]

You are ALL wrong...it is the GHOST OF RODAN flying up to another galaxy!!!!!

I watched RODAN the other night and it looks just like him....

Now I am into the Mothra Movies as I finished the Godzilla Movies... And that is RODAN, I tell you...

Really nice picture!!!!! Nice colors!!!

Another, less colorful, but very spectacular photo from Tony Hallas, can be found here...
http://apod.nasa.gov/apod/ap070427.html

In that photo, you can see more trailing stars in the upper left part of M81.
I think the "Ghost of Rodan" is our foreground dust.

:---[===] *

[K1NS]

In the photo, M81's "bright yellow core" looks like a large yellow star, like our sun, but of course it is actually lots of individual objects (stars), with lots of "empty" space between the objects.

But isn't our sun actually lots of individual objects (neutrons, protons, etc.) with lots of "empty" space between the objects? Isn't this true of all matter (with the exceptions of neutron stars, black holes, and the universe at t=0)?

As an untrained ponderer of cosmology, one of my biggest personal revelations has been the notion that solid objects are, in fact, an illusion. The table this laptop rests on is mostly empty space, as is the laptop, and the only thing that prevents the laptop from passing through the table are the nuclear forces. I have tried to explain this to friends and family, but I do not have the vocabulary to express the idea adequately.

I believe that looking at this photo truly expresses the idea of "solid" matter as "empty" space, and helps us to understand it.

[LocalColor]

A "grand" photo! Lovely and lots of interesting info in the text. Thank you Bernard Miller and APOD.

[Boomer12k]

In the photo, M81's "bright yellow core" looks like a large yellow star, like our sun, but of course it is actually lots of individual objects (stars), with lots of "empty" space between the objects.

But isn't our sun actually lots of individual objects (neutrons, protons, etc.) with lots of "empty" space between the objects? Isn't this true of all matter (with the exceptions of neutron stars, black holes, and the universe at t=0)?

As an untrained ponderer of cosmology, one of my biggest personal revelations has been the notion that solid objects are, in fact, an illusion. The table this laptop rests on is mostly empty space, as is the laptop, and the only thing that prevents the laptop from passing through the table are the nuclear forces. I have tried to explain this to friends and family, but I do not have the vocabulary to express the idea adequately.

I believe that looking at this photo truly expresses the idea of "solid" matter as "empty" space, and helps us to understand it.

You explained it adequately for me... And there are many illusions in the Universe. The Universe IS ENERGY!!! So are the particles...built up, combinations of energies....

As for the Atom...even though it is said that 90 percent of the atom is space...how much space is that actually????? About 0.3 nanometers in diameter...we are not talking a very large amount of space for all that 90 percent. Atoms also conglomerate or bond into a bigger chunk. The Molecule, (Yes, CHRIS, I know Even the Hydrogen atom is still a molecule). Water, H2O is not an atom, but combined atoms. So a bigger block. This becomes molecular BLOCKS. Fibers. Long strands, etc...the DENSITY increases and the Mass of the material increases. You cannot put your hand through the desk...but a lake full of water, you can swim in, though way more MASSIVE that you are. Different state of matter, but still massive, still negative charge around the atoms, repelling your atoms. But now it is not really atoms, or molecular blocks....but THE CELL! US!!! We are CELLS! And large combinations of cells at different layers, that give us mass and density. The cell against the FIBERS of the wood in the table...That is another reason why, AT THE LARGE SCALE, your hand won't go through the table. Or your laptop. The FIBERS, and CRYSTALLINE Structures ARE JUST TOO BIG!!!!
If I take two strong magnets, and put the north poles at each other it is hard to put them together, but it can be done. But you can't put your hand through the desk...if it were JUST THE NUCLEAR FORCE, OR ELECTRO-MAGNETIC FORCE... you should AT LEAST be able to MOVE THOSE ATOMS OUT OF THE WAY!!!! BUT THAT IS NOT IT....at least, that is not ONLY... it... It is the BONDING INTO LARGER, DENSER MATERIALS...and the real reason...my opinion...is the DENSITY OF THE MATERIAL.

My observation...
:---[===] *

[JohnD]

Looks like I must answer my own question, so get Googling.

Turns out what I took as 'Arp's Loop' wasn't.
It's the dark lines across the core from three to five o'clock on the APOD image. They cut right across the spiral structure of M81, and I can easily see now how they might be a lot nearer! But difficult to measure the distance as they are dark.

JOhn

[retrogalax]

,

This galaxy is intriguing with that shape, simple spiral, symmetrical. Something intriguing too is the relative short distance between 2 galaxies in comparison of their size, if they are considered individually.
The spiral shape evokes a rotation, rotation around the bulge or uniform rotation from the whole. I don't know if we can see those movements, it seems too big to see a change in orientation or in diameter for example and
indeed a photography like that one remains a good way to discern those beautiful (and intriguing) structures.

Retrogalaxy

[bystander]

Arp's Loop Is Not What It Seems

Arp's Loop and NGC3031 (M81) in Ursa Major
A Multi-wavelength analysis of M81: insight on the nature of Arp's loop

APOD: M81 and Arp's Loop (2010 Dec 09)
APOD: The M81 Galaxy Group Through the Integrated Flux Nebula (2012 Mar 13)