Starship Asterisk*

by **Ann** » Sat Nov 23, 2019 6:52 am

Tara_Li wrote: ↑Sat Nov 23, 2019 4:00 am
Ann wrote: ↑Fri Nov 22, 2019 6:28 am
Tara_Li wrote: ↑Thu Nov 21, 2019 10:50 pm

Not sure what you're identifying as the elongated bulge - I'm looking at the tiny, circular as far as I can tell, bright central spot that the dust lanes come right up to and touch - but don't seem to enter. It only appears to be about 15 pixels in diameter.
Look at the picture at left. As you can see, the primary bar is a long, broad, rather faint yellowish structure. M61 has just such a bar. Can you see it? Note that the bar is "horizontal" in the illustration at left, but in the picture of M61, the bar is diagonally orientated.
...
At right you can see a comparison between a barred and an unbarred galaxy. In the unbarred galaxy (M101, left) the spiral arms start right at the (round) center. In NGC 7773, there is a yellowish horizontal structure sticking out from the round yellowish center. That is the bar. The spiral arms start at the ends of the bar.

Ann
Ok, I think I've identified the "bar" that you're considering part of the galactic core. It doesn't feel like particularly part of the core - it's way out from it, in fact.

It seems like the arms go way, way in, all the way to the real core.

: Click to view full size image

Messier 61. ESA/Hubble & NASA.
Acknowledgements: G. Chapdelaine, L. Limatola, and R. Gendler.

: Click to view full size image

Barred galaxy NGC 1097. Photo: ESO/Rob Gendler.

You really did find the bar of M61, Tara_Li. I agree with you that the long bar of M61 is not really a part of the core of this galaxy. All large galaxies have small, compact cores, surrounding a central black hole. In most cases the small core of the galaxy is very bright, too.

(Check out this infrared image of the the central part of the Milky Way by NASA/ESA/JPL/Q.D. Wang/S. Stolovy if you feel like it. The white "maelstrom" at lower right is the central black hole surrounded by lots of bright stars in tight orbits around it, as far as I can understand. It is not certain that our galaxy has an inner ring around its black hole that is nearly as bright and pronounced as the inner rings of M61 and NGC 1097.)

Back to M61. It is somewhat hard to see the different components of M61, because M61 has so much star formation that its arms are broad, uneven and "messy". But no, the arms of M61 does not go all the way to its core.

Compare M61 with NGC 1097, whose structure is much "cleaner" and easier to see. Just like M61, NGC has a small core with a supermassive black hole in its center. Just like M61, NGC 1097 has a small bright inner ring surrounding the compact core. Just like M61, NGC 1097 has a long broad elliptical-shaped yellowish bar. Just like M61, NGC 1097 has two long curved dust lanes emanating from the inner bright ring and connecting the inner ring with the blue starforming arms which start at the ends of the bar. The curved dust lanes inside the bar are not considered parts of the arms.

You can see other dust structures in the bulge, not just the two main long dark dust lanes connecting the inner ring with the arms. Those dust structures are also not parts of the arms.

Unlike M61, NGC 1097 has a bright outer bluish ring surrounding the yellowish bulge. In M61 the arms are a bit of a mess, because they are so broad and uneven, and no clear outer ring surrounding the bar can be easily seen.

Also unlike M61, NGC 1097 has long, rather narrow spiral arms that clearly start at the ends of the bar. The structure of M61 is much messier (that's funny because M61 is really Messier 61), and the bar structure of M61 is not as pronounced as the bar structure of NGC 1097.

Ann

by **neufer** » Sat Nov 23, 2019 4:57 am

Tara_Li wrote: ↑Sat Nov 23, 2019 4:00 am
It seems like the arms go way, way in, all the way to the real core.

`Twas brillig, and the slithy toves
Did gyre and gimble in the wabe;
All mimsy were the borogoves,
And the mome raths outgrabe.
`That’s enough to begin with,’ Humpty Dumpty interrupted: `there are plenty of hard words there. “Brillig” means four o’clock in the afternoon — the time when you begin broiling things for dinner.’

`That’ll do very well,’ said Alice: and “slithy”?’

`Well, “slithy” means “lithe and slimy.” “Lithe” is the same as “active.” You see it’s like a portmanteau — there are two meanings packed up into one word.’

`I see it now,’ Alice remarked thoughtfully: `and what are “toves”?’

`Well, “toves” are something like badgers — they’re something like lizards — and they’re something like corkscrews.’

`They must be very curious looking creatures.’

`They are that,’ said Humpty Dumpty: `also they make their nests under sun-dials — also they live on cheese.’

`Andy what’s the “gyre” and to “gimble”?’

`To “gyre” is to go round and round like a gyroscope. To “gimble” is to make holes like a gimblet.’

`And “the wabe” is the grass-plot round a sun-dial, I suppose?’ said Alice, surprised at her own ingenuity.

`Of course it is. It’s called “wabe,” you know, because it goes a long way before it, and a long way behind it — ‘

`And a long way beyond it on each side,’ Alice added.

`Exactly so.

by **Tara_Li** » Sat Nov 23, 2019 4:00 am

Ann wrote: ↑Fri Nov 22, 2019 6:28 am
Tara_Li wrote: ↑Thu Nov 21, 2019 10:50 pm
Ann wrote: ↑Wed Aug 28, 2019 11:19 am
Galactic cores are usually quite compact, but the yellowish, elongated bulge (really a bar) of M61 is not that small.
Not sure what you're identifying as the elongated bulge - I'm looking at the tiny, circular as far as I can tell, bright central spot that the dust lanes come right up to and touch - but don't seem to enter. It only appears to be about 15 pixels in diameter.
Look at the picture at left. As you can see, the primary bar is a long, broad, rather faint yellowish structure. M61 has just such a bar. Can you see it? Note that the bar is "horizontal" in the illustration at left, but in the picture of M61, the bar is diagonally orientated.
...
At right you can see a comparison between a barred and an unbarred galaxy. In the unbarred galaxy (M101, left) the spiral arms start right at the (round) center. In NGC 7773, there is a yellowish horizontal structure sticking out from the round yellowish center. That is the bar. The spiral arms start at the ends of the bar.

Ann

Ok, I think I've identified the "bar" that you're considering part of the galactic core. It doesn't feel like particularly part of the core - it's way out from it, in fact.

It seems like the arms go way, way in, all the way to the real core.

by **Ann** » Fri Nov 22, 2019 6:28 am

Tara_Li wrote: ↑Thu Nov 21, 2019 10:50 pm
Ann wrote: ↑Wed Aug 28, 2019 11:19 am
Tara_Li wrote: ↑Wed Aug 28, 2019 5:52 am To my eye, that core region looks abnormally small - is that an effect of the wavelength, or is the core just unusually compact?
Galactic cores are usually quite compact, but the yellowish, elongated bulge (really a bar) of M61 is not that small.
Not sure what you're identifying as the elongated bulge - I'm looking at the tiny, circular as far as I can tell, bright central spot that the dust lanes come right up to and touch - but don't seem to enter. It only appears to be about 15 pixels in diameter.

: Click to view full size image

Messier 61. ESA/Hubble & NASA.
Acknowledgements: G. Chapdelaine, L. Limatola, and R. Gendler.

: Click to view full size image

Components of double-barred spiral galaxy. Credit: ESO.

Look at the picture at left. As you can see, the primary bar is a long, broad, rather faint yellowish structure. M61 has just such a bar. Can you see it? Note that the bar is "horizontal" in the illustration at left, but in the picture of M61, the bar is diagonally orientated.

: Click to view full size image

Unbarred galaxy M101 (left) and barred galaxy NGC 7773 (right).
ESA and NASA. See more here.

At right you can see a comparison between a barred and an unbarred galaxy. In the unbarred galaxy (M101, left) the spiral arms start right at the (round) center. In NGC 7773, there is a yellowish horizontal structure sticking out from the round yellowish center. That is the bar. The spiral arms start at the ends of the bar.

Ann

by **Tara_Li** » Thu Nov 21, 2019 10:50 pm

Ann wrote: ↑Wed Aug 28, 2019 11:19 am
Tara_Li wrote: ↑Wed Aug 28, 2019 5:52 am To my eye, that core region looks abnormally small - is that an effect of the wavelength, or is the core just unusually compact?
Galactic cores are usually quite compact, but the yellowish, elongated bulge (really a bar) of M61 is not that small.

Not sure what you're identifying as the elongated bulge - I'm looking at the tiny, circular as far as I can tell, bright central spot that the dust lanes come right up to and touch - but don't seem to enter. It only appears to be about 15 pixels in diameter.

by **noahstrickland@gmail.com** » Thu Aug 29, 2019 11:17 pm

Have been looking at APOD for a decade now if not more, never posted or thought to post. The reason I am commenting this evening is to say thanks for having this website in the first place and secondly to say that this is maybe the best APOD pic yet. For real, it's stunning and amazing and I really can't think of a better one.

I do love me some galaxy pics though, so I am definitely biased in my opinion.

keep up the awesome work!

by **Chris Peterson** » Thu Aug 29, 2019 1:44 pm

DL MARTIN wrote: ↑Wed Aug 28, 2019 11:34 pm Thank you Ann for a thoughtful and gracious reply. Unfortunately I'm of the opinion that the astronomy community sells the idea that everything is current events and, by extension, approachable. When the time context is applied however, the 'current events' concept doesn't add up. I view it as if i'm looking out in my garden and viewing the lawn as evidence that the Earth is flat. Events that take place between, for example, the light from Andromeda reaching us and in Andromeda itself seem unaccounted for. The failure to acknowledge this analytic shortcoming undermines astronomy's fundamental credibility.

Not everything is treated as "current". But something like this image is, because... well, for most scientific purposes, it is. And where it isn't... as with intervening events... those things are considered.

by **DL MARTIN** » Wed Aug 28, 2019 11:34 pm

Thank you Ann for a thoughtful and gracious reply. Unfortunately I'm of the opinion that the astronomy community sells the idea that everything is current events and, by extension, approachable. When the time context is applied however, the 'current events' concept doesn't add up. I view it as if i'm looking out in my garden and viewing the lawn as evidence that the Earth is flat. Events that take place between, for example, the light from Andromeda reaching us and in Andromeda itself seem unaccounted for. The failure to acknowledge this analytic shortcoming undermines astronomy's fundamental credibility.

by **Ann** » Wed Aug 28, 2019 10:01 pm

DL MARTIN wrote: ↑Wed Aug 28, 2019 6:55 pm Again, without context doubt remains that 2=2=4. In other words, if the fact that what is being visualized is 55 millions years ago (but not stated), then how can one validate conclusions as if in the present. To exclude the time variable (t=o) is to dismiss evolution. This just doesn't add up.

55 million years isn't that long in the life of most stars. Admittedly, it can be very long, and more than the lifetime, of a massive star. The light that we see from M61 is dominated by the emission of massive stars, and many of them will have died since they produced the light that reaches us today. On the other hand, the "frozen in time" image of M61 that is the only picture we can ever receive of it gives every impression of making many new stars "now". So even if many of the bright stars that we can see in our "snapshot in time" of M61 have died by "now", many other bright stars have undoubtedly been born.

: Click to view full size image

The Andromeda Galaxy. Source:
https://www.physicsforums.com/threads/h ... rs.707502/

But it is really meaningless to talk about "now" when we discuss other galaxies. When I was 15 years old, I saw M31, the Andromeda galaxy, through a pair of smallish binoculars. My first view of Andromeda is still the most magical thing that I have ever seen in the sky. What made the experience so powerful was that I felt totally certain that there was another "person" in that blurry spot in the sky. Someone was alive in there. There were habitated worlds in there, and someone in there was actually looking back at me. I felt an overpoweringly strong urge to wave at the person that I was "looking at".

The memory has always stayed with me, but as I kept thinking of waving at the "person" I had imagined in the blurry spot that was Andromeda, I began realizing how impossible my greeting actually was. If by some magical means the waving of my hand could actually be translated into a signal that eventually reached the person I had imagined in Andromeda, then it would take two million years for my greeting to arrive at its destination in our sister galaxy.

If the person that I had waved at had a life span that was even remotely as short as my own, then that person would have died eons before my wave signal actually reached him or her. And if that person waved back at me at that moment when I felt that incredible connection reaching from myself to Andromeda, then that person's wave signal wouldn't reach the Earth until I had been dead for about two million years.

It's useless to talk about what things are like "now" in other galaxies. We get the pictures of them that we get based on the photons emitted by them some time in the past, and that is the best we can do. That is all we can do.

Ann

by **TrickyGlow** » Wed Aug 28, 2019 9:48 pm

I was gonna ask something but then I remembered I just saw the galaxy type chart and am laughing my ass off at the SAD SAM galaxy types.

by **DL MARTIN** » Wed Aug 28, 2019 6:55 pm

Again, without context doubt remains that 2=2=4. In other words, if the fact that what is being visualized is 55 millions years ago (but not stated), then how can one validate conclusions as if in the present. To exclude the time variable (t=o) is to dismiss evolution. This just doesn't add up.

by **dlw** » Wed Aug 28, 2019 5:53 pm

Beautiful image!
FWIW I noted a very cute little (apparently) barred spiral galaxy near the right edge. Presumably much farther away than M61.

by **neufer** » Wed Aug 28, 2019 12:48 pm

https://en.wikipedia.org/wiki/Messier_61 wrote:

<<Messier 61 is an intermediate barred spiral galaxy: i.e., a galaxy that is in between the classifications of a barred spiral galaxy and an unbarred spiral galaxy. It is designated as SAB in the galaxy morphological classification system devised by Gerard de Vaucouleurs. Subtypes are labeled as SAB0, SABa, SABb, or SABc, following a sequence analogous to the Hubble sequence for barred and unbarred spirals. The subtype (0, a, b, or c) is based on the relative prominence of the central bulge and how tightly wound the spiral arms are.

M61 belongs to a smaller subgroup known as the S Cloud. The morphological classification of SAB(rs)bc indicates a weakly-barred spiral (SAB) with the suggestion of a ring structure (rs) and moderate to loosely wound spiral arms. It has an active galactic nucleus and is classified as a starburst galaxy containing a massive nuclear star cluster with an estimated mass of 10⁵ solar masses and an age of 4 million years, as well as a central candidate supermassive black hole weighing around 5×10⁶ M☉ solar masses. It cohabits with an older massive star cluster as well as a likely older starburst. Evidence of significant star formation and active bright nebulae appears across M61's disk. Unlike most late-type spiral galaxies within the Virgo Cluster, M61 shows an unusual abundance of neutral hydrogen (H I).>>

by **NCTom** » Wed Aug 28, 2019 11:26 am

Thanks Ann. That helps a lot. I was wondering the same thing as the bar was not immediately obvious.

by **Ann** » Wed Aug 28, 2019 11:19 am

Tara_Li wrote: ↑Wed Aug 28, 2019 5:52 am To my eye, that core region looks abnormally small - is that an effect of the wavelength, or is the core just unusually compact?

: Click to view full size image

Messier 61. ESA/Hubble & NASA.
Acknowledgements: G. Chapdelaine, L. Limatola, and R. Gendler.

Galactic cores are usually quite compact, but the yellowish, elongated bulge (really a bar) of M61 is not that small.

Ann

by **orin stepanek** » Wed Aug 28, 2019 11:10 am

Tara_Li wrote: ↑Wed Aug 28, 2019 5:52 am To my eye, that core region looks abnormally small - is that an effect of the wavelength, or is the core just unusually compact?

Probably depends on the size of the supermassive black hole!!

by **Tara_Li** » Wed Aug 28, 2019 5:52 am

To my eye, that core region looks abnormally small - is that an effect of the wavelength, or is the core just unusually compact?

by **Ann** » Wed Aug 28, 2019 4:32 am

M61 is a gorgeous spiral, and it looks even more gorgeous in the Hubble/Gendler/Colombari portrait of it.

Ann

by **APOD Robot** » Wed Aug 28, 2019 4:12 am

Messier 61 Close Up

Explanation: Image data from the Hubble Space Telescope, the European Southern Observatory, and small telescopes on planet Earth are combined in this magnificent portrait of face-on spiral galaxy Messier 61 (M61). A mere 55 million light-years away in the Virgo Cluster of Galaxies, M61 is also known as NGC 4303. It's considered to be an example of a barred spiral galaxy similar to our own Milky Way. Like other spiral galaxies, M61 also features sweeping spiral arms, cosmic dust lanes, pinkish star forming regions, and young blue star clusters. The bright galactic core is offset to the left in this 50 thousand light-year wide close-up.

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