Starship Asterisk*

UGC 12591: The Fastest Rotating Galaxy Known

Explanation: Why does this galaxy spin so fast? To start, even identifying which type of galaxy UGC 12591 is difficult -- featured on the lower left, it has dark dust lanes like a spiral galaxy but a large diffuse bulge of stars like a lenticular. Surprisingly observations show that UGC 12591 spins at about 480 km/sec, almost twice as fast as our Milky Way, and the fastest rotation rate yet measured. The mass needed to hold together a galaxy spinning this fast is several times the mass of our Milky Way Galaxy. Progenitor scenarios for UGC 12591 include slow growth by accreting ambient matter, or rapid growth through a recent galaxy collision or collisions -- future observations may tell. The light we see today from UGC 12591 left about 400 million years ago, when trees were first developing on Earth.

<< Previous APOD

This Day in APOD

Next APOD >>

Love the note that its light comes from when trees were first beginning on Earth. Great thought.

It is interesting to compare today's APOD with the original image of this galaxy, published on Space Telescope's own website.

As you can see, the color balance of the APOD is much bluer, so blue that the lenticular, "red and dead" barred galaxy at upper right looks blue, even though it totally lacks any sign of star formation. The likely reason for the blue color balance of the APOD is that the original image is a two-filter image, where the filters are 606 nm (centered on orange) and 814 nm (near infrared). Presumably the 606 nm filter image has been treated as blue in the APOD, or at least a bright shade of cyan. In my opinion, there is very little "true cyan" in UGC 12591 or in any of its neighboring galaxies, which is to say that the original Space Telescope image looks much more "natural" to me.

The details in the dust lane of UGC 12591 have also been sharpened in the APOD.

I love the "speed line" appearance of the dust lane, as if it was taken out of a Disney cartoon.

Apart from the speed line effect, however, UGC 12591 reminds me of the Sombrero galaxy, M104.






















Obviously UGC 12591 and M104 are far from identical. The halo of M104 is much larger and brighter than the one of UGC 12591. Also M104, while probably lacking in any sort of high-mass star formation, nevertheless almost certainly contains pockets of "young-ish" stars of, perhaps, late spectral class A. The moderately young stars of M104 are probably embedded in the dust disk of this galaxy. UGC 12591, by contrast, appears to have a dust disk that is devoid of anything but dust. Also the dust lane of M104 doesn't look like dizzying racing stripes!






























It would appear that inner dust lanes are common in lenticular galaxies. Note in the dust lane of NGC 6861 a tiny speck of blue in the dust lane (at lower left), so there might be a little bit of star formation going on there after all. The dust disk of NGC 6861 does seem more substantial than the thin dust arms of NGC 2728.

Ann

How can a rotation be stated as [km/s]?
Wouldn't [rad/s] be more logical?

apodJona wrote: ↑Wed Feb 19, 2020 8:34 am How can a rotation be stated as [km/s]?
Wouldn't [rad/s] be more logical?

||v|| = r . omega

Alex

Alex_515 wrote: ↑Wed Feb 19, 2020 9:11 am ||v|| = r . omega

Certainly, but how is the radius defined here?
Is it the 'outer' radius of the galaxy?

After stating that rotations cannot be given in linear speed units (without specifying radius), I suppose that our commonly experienced on Earth rotation rates (360° in seconds or fractions of second, in 24 hours, in 28 days, in 365 days) cannot help. A galaxy probably takes million years to make a full turn (can anybody be more more precise ? ) that's making the radiant/s unit a completely out of scale choice.
Nonetheless that's the beauty of the Universe.
Happy every day in starting my activities with APOD !

If I recall arightly, Earth takes about 250 million years to go around the center of our galaxy.

I guess I never paid any attention to how fast a galaxy spins before; or if any spin faster than others!

If the claim is made that it's 'the 'fastest rotating', then the claim needs to be supported by data in rotational units. These can be rad/S, or km/S at a given radius, but km/S on its own is meanngless. But even a correclly chosen rotation unit needs to have the particular smeasurement radius defined, because it seems dynamically impossible that the entire galaxy is rotating as one soiid disk. Rotation rate curves from spectral Doppler shifts across the glaxy would make this a much more informative claim....

isoparix wrote: ↑Wed Feb 19, 2020 12:57 pm
If the claim is made that it's 'the fastest rotating', then the claim needs to be supported by data in rotational units.

These can be rad/S, or km/S at a given radius, but km/S on its own is meaningless.

It's just that spinning/rotating 'rigid body terminology' is awkward when discussing a galaxy.

Perhaps: UGC 12591: The Fastest Known Orbital Velocities would have been preferable.

I'm rather fond of the starfish looking galaxy above the prominent galaxy.Odd how one of it's arms looks distorted/aligned differently.So many galaxies! I was just wondering why there is not an even larger density of galaxies in the Universe.(Trillions instead of Billions)

OK. There ARE Trillions of galaxies.Mind boggling.

Ann wrote: ↑Wed Feb 19, 2020 7:29 am

UGC 12591: The Fastest Rotating Galaxy Known Image Credit: NASA, ESA, Hubble; Processing & Copyright: Leo Shatz

---

UGC 12591. Image from https://www.spacetelescope.org/images/potw1709a/.

---

It is interesting to compare today's APOD with the original image of this galaxy, published on Space Telescope's own website.

As you can see, the color balance of the APOD is much bluer, so blue that the lenticular, "red and dead" barred galaxy at upper right looks blue, even though it totally lacks any sign of star formation. The likely reason for the blue color balance of the APOD is that the original image is a two-filter image, where the filters are 606 nm (centered on orange) and 814 nm (near infrared). Presumably the 606 nm filter image has been treated as blue in the APOD, or at least a bright shade of cyan. In my opinion, there is very little "true cyan" in UGC 12591 or in any of its neighboring galaxies, which is to say that the original Space Telescope image looks much more "natural" to me.

The details in the dust lane of UGC 12591 have also been sharpened in the APOD.

...
Ann

I acknowledge the sin of having too much of the blue color in galaxies halos, as I also thought it could be wrong in attempt to simulate "natural colors" from bi-color data. I was trying to make a clearer view of faint galaxies in the background as well as making the dust lanes more visible, while reducing the green cast of the original image. It's interesting to know that raw linear image has quite bright halo at the center of UGC 12591, which essentially hides all details of the core and some of the the galaxy's ring structure at its distant side. The APOD image brings out these details at the expense of making that central halo much dimmer.

BTW, I couldn't find catalog name of the galaxy at upper right corner, and therefore no description of it.

Leo Shatz

The dust lanes appear circular, not spiral, like a pebble dropped into calm waters. Gravity waves from the super-massive black hole? I don't believe in dark matter, methinks the gravitational effects of the black hole are severely underestimated, but then, my feeble understanding of such matters dismisses my blathering twaddle.

apodJona wrote: ↑Wed Feb 19, 2020 8:34 am How can a rotation be stated as [km/s]?
Wouldn't [rad/s] be more logical?

So, here's the thing about the rotations of disk galaxies.

• Our first expectation was Keplerian rotational motions, so that the farther a star is from the center of the galaxy, the slower its rotation in terms of km/s and even more pronounced -- an inverse square relation -- its slowing if measured in rad/s.
• It was surprising, though, when rotational motions were measured. You might think that what was surprising was that the whole thing rotated as a solid object, so that everything in the disk rotated much more rapidly in km/s as you went out, all maintaining a roughly constant rad/s (and km/s would go up linearly with radius).

  

• Actually, the observations are in between these two. Although the stars do not rotate with a consistent rad/s, as one goes from the center to the edge, the km/s measurements are surprisingly consistent.

  Wikipedia: Galaxy rotation curve
  Stars revolve around their galaxy's centre at equal or increasing speed over a large range of distances.

  

  Thanks to Prof. Richard Pogge, Lecture 41: Dark Matter & Dark Energy, http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit6/Images/rotcur2.gif

  ---

  The curves would be more informative, as @isoparix said, but as a first measure, for many galaxies, an approximate single value of km/s does give an overall characterization that is quite meaningful. Without having the actual rotational curve for UGC 12591, I suspect it looks like the image above, but with the high point on the y-axis labelled at 500 km/s instead of 200 km/s.

And that extreme value of 500 km/s is UGC 12591's claim to fame.

spinlock wrote: ↑Wed Feb 19, 2020 4:57 pm ... I was trying to make a clearer view of faint galaxies in the background as well as making the dust lanes more visible ...
Leo Shatz

You succeeded beautifully, I think. I greatly enjoyed looking around at that menagerie of surrounding galaxies.

spinlock wrote: ↑Wed Feb 19, 2020 4:57 pm I acknowledge the sin of having too much of the blue color in galaxies halos, as I also thought it could be wrong in attempt to simulate "natural colors" from bi-color data. I was trying to make a clearer view of faint galaxies in the background as well as making the dust lanes more visible, while reducing the green cast of the original image. It's interesting to know that raw linear image has quite bright halo at the center of UGC 12591, which essentially hides all details of the core and some of the the galaxy's ring structure at its distant side. The APOD image brings out these details at the expense of making that central halo much dimmer

It is wise to not worry about any color absolutes when you're working with data that can't provide that. Much better to focus on the particular details you want to bring out, and base your color decisions on that... not on any vague sense of "natural".

What happened to the theory that dark matter held together a fast spinning galaxy?

jeffplay wrote: ↑Wed Feb 19, 2020 7:37 pm
What happened to the theory that dark matter held together a fast spinning galaxy?

https://en.wikipedia.org/wiki/Milky_Way wrote:
<<Stars and gases at a wide range of distances from the Milky Way's Galactic Center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much (about 90%) of the (0.8–1.5×10¹² M_☉) mass of the Milky Way is invisible to telescopes, neither emitting nor absorbing electromagnetic radiation. This conjectural mass has been termed "dark matter". The rotational period is about 240 million years at the radius of the Sun.>>

For UGC 12591 to have twice the Milky Way's orbital speeds it must either be:

• 1) 4 times as massive or
  2) 4 times as compact.

or some combination of the two.

What is the 'object' in the upper right?

hypatia wrote: ↑Thu Feb 20, 2020 12:01 am What is the 'object' in the upper right?

Another galaxy.

MarkBour wrote: ↑Wed Feb 19, 2020 6:11 pm

spinlock wrote: ↑Wed Feb 19, 2020 4:57 pm ... I was trying to make a clearer view of faint galaxies in the background as well as making the dust lanes more visible ...
Leo Shatz

You succeeded beautifully, I think. I greatly enjoyed looking around at that menagerie of surrounding galaxies.

I agree. I should have mentioned in my original comment that the background galaxies do indeed look sharper and more interesting in your image than in the original Space Telescope one.

Ann

I'm going to search for the name/ designation of the large upper right galaxy.If anyone knows already please chime in.

Chris Peterson wrote: ↑Thu Feb 20, 2020 12:18 am

hypatia wrote: ↑Thu Feb 20, 2020 12:01 am What is the 'object' in the upper right?

Another galaxy.

I figured that BUT which galaxy is it?