APOD: Rings and Bar of Spiral Galaxy NGC 1398 (2023 Jul 12)

[APOD Robot]

Rings and Bar of Spiral Galaxy NGC 1398

Explanation: Why do some spiral galaxies have a ring around the center? Spiral galaxy NGC 1398 not only has a ring of pearly stars, gas and dust around its center, but a bar of stars and gas across its center, and spiral arms that appear like ribbons farther out. The featured deep image from Observatorio El Sauce in Chile shows the grand spiral galaxy in impressive detail. NGC 1398 lies about 65 million light years distant, meaning the light we see today left this galaxy when dinosaurs were disappearing from the Earth. The photogenic galaxy is visible with a small telescope toward the constellation of the Furnace (Fornax). The ring near the center is likely an expanding density wave of star formation, caused either by a gravitational encounter with another galaxy, or by the galaxy's own gravitational asymmetries.

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[shaileshs]

Ummmm... "Bar of stars" ? Where ?

[Ann]

Wow. Mark Hanson and Mike Selby create such stunning galaxy images. And NGC 1398 is such a stunning galaxy. You can tell that it is an isolated galaxy that has been left to its own devices, because it is so picture perfect and symmetrical. No outside forces have disturbed its magnificent symmetry!

It’s like that classic poem, ”Tyger, tyger, burning bright, in the forest of the night, what immortal hand or (knee?) dared frame your fearful symmetry?”

I’m quoting from memory. As you can hear. I can barely do a thing with this stupid little mobile phone. I can barely convince it to write anything in English, because it is trying to change almost every English word I write into something that is used in Swedish, no matter how preposterous the Swedish word might be in the given context. Of course, my spellcheck doesn’t understand context, only Swedish words. Groan!!!

But like I said, the APOD is stunning!

Ann

[Roy]

The picture appears to be about 35 degrees top oblique view of a remarkably circular galaxy. Forces at work are uniform. The explanation, however, makes no sense whatever. It is time to get off the Big Bang, gravity only, black hole paradigm.

Can the rotational velocities be measured on this? Asking for a friend.

[orin stepanek]

Unusual shape on this galaxy; but it is still beautiful!

[Chris Peterson]

The picture appears to be about 35 degrees top oblique view of a remarkably circular galaxy. Forces at work are uniform. The explanation, however, makes no sense whatever. It is time to get off the Big Bang, gravity only, black hole paradigm.

Can the rotational velocities be measured on this? Asking for a friend.

All spiral galaxies are circular, unless they've been recently perturbed. The explanation is perfectly reasonable and can be tested with simulations.

I'm sure that the rotational speeds can be measured, although as we approach face-on the accuracy will diminish.

[Sa Ji Tario]

Ummmm... "Bar of stars" ? Where ?

The "star bar" looks almost vertical

[zendae1]

"...although as we approach face-on the accuracy will diminish."

Why would this be so? How does closer observation (as miniscule as that is) lessen clarity of data?

[Roy]

Density waves - analogous to sound in gases, discredited long ago. Gravitational encounter - nothing nearby. Gravitational anomaly - word salad, for “I don’t know”.
A negative of this picture would be interesting, because the spiral arms appear to faintly show at least half again farther out than the “ribbons” referred to.

Is there some way to get sideways velocity? Spreading of spectral lines or something? What I read so far is about getting approach and recede velocity, averaging them, and then constructing a velocity curve from those plots.

[VictorBorun]

The picture appears to be about 35 degrees top oblique view of a remarkably circular galaxy. Forces at work are uniform. The explanation, however, makes no sense whatever. It is time to get off the Big Bang, gravity only, black hole paradigm.

Can the rotational velocities be measured on this? Asking for a friend.

All spiral galaxies are circular, unless they've been recently perturbed. The explanation is perfectly reasonable and can be tested with simulations.

I'm sure that the rotational speeds can be measured, although as we approach face-on the accuracy will diminish.

To present this APOD as face-on let's rotate it by 350.6°and stretch vertically by the factor of 1.3498.
The label shows the direction where the dust is better backlighted by the core sphere (after stretching vertically the core sphere looks like ellipsoid).
This way it is easier to trace what looks like two identical dust lane arms from the inner ring to the outer one (the dust seen better where the lane is toward the observer from the center of the Galaxy NGC 1398):

...

Click to view full size image 1 or image 2

[Chris Peterson]

"...although as we approach face-on the accuracy will diminish."

Why would this be so? How does closer observation (as miniscule as that is) lessen clarity of data?

Because rotational speeds are measured by looking at Doppler shift of light, whereby material moving towards us is redshifted and away from us is blueshifted. When we view a galaxy fully face-on all of the motion is perpendicular to our line-of-site, so there is no Doppler shift to measure.

[AVAO]

Wow. Mark Hanson and Mike Selby create such stunning galaxy images. And NGC 1398 is such a stunning galaxy. You can tell that it is an isolated galaxy that has been left to its own devices, because it is so picture perfect and symmetrical. No outside forces have disturbed its magnificent symmetry!

It’s like that classic poem, ”Tyger, tyger, burning bright, in the forest of the night, what immortal hand or (knee?) dared frame your fearful symmetry?”
...
But like I said, the APOD is stunning!

Ann

ThanX Ann

Apparently we like the same lyrics by the same poets
How high the symmetry in galaxies can be easily determined.
Cut in half, flip once vertically and once horizontally.

PS.: I like the pictures of me, my friends or whoever
to mirror axially and to compare the two resulting images.
These are infinitely revealing. I'm left handed and my hard side is my soft side...

Click to view full size image 1 or image 2

[johnnydeep]

"...although as we approach face-on the accuracy will diminish."

Why would this be so? How does closer observation (as miniscule as that is) lessen clarity of data?

Because rotational speeds are measured by looking at Doppler shift of light, whereby material moving towards us is redshifted and away from us is blueshifted. When we view a galaxy fully face-on all of the motion is perpendicular to our line-of-site, so there is no Doppler shift to measure.

I think you must mean "material moving towards us is blueshifted and away from us is redshifted".

[Chris Peterson]

"...although as we approach face-on the accuracy will diminish."

Why would this be so? How does closer observation (as miniscule as that is) lessen clarity of data?

Because rotational speeds are measured by looking at Doppler shift of light, whereby material moving towards us is redshifted and away from us is blueshifted. When we view a galaxy fully face-on all of the motion is perpendicular to our line-of-site, so there is no Doppler shift to measure.

I think you must mean "material moving towards us is blueshifted and away from us is redshifted".

Correct.

[Avalon]

Any explanation as to what we think causes bars to form and remain as structures in galaxies?

[Leon1949Green]

What about the little galaxy to the right? Is it a satellite of NGC 1398, or more distant? Thanks.

[Ann]

What about the little galaxy to the right? Is it a satellite of NGC 1398, or more distant? Thanks.

It is definitely more distant. You can easily tell that its blue regions of star formation are much blurrier and much less well resolved than the blue regions of NGC 1398.

Ann

[shaileshs]

Ummmm... "Bar of stars" ? Where ?

The "star bar" looks almost vertical

Yep, I almost didn't realize it'd be vertical. Thanks.