Explanation: Why are these galaxies spinning so fast? If you estimated each spiral's mass by how much light it emits, their fast rotations should break them apart. The leading hypothesis as to why these galaxies don't break apart is dark matter -- mass so dark we can't see it. But these galaxies are even out-spinning this break-up limit -- they are the fastest rotating disk galaxies known. It is therefore further hypothesized that their dark matter halos are so massive -- and their spins so fast -- that it is harder for them to form stars than regular spirals. If so, then these galaxies may be among the most massive spirals possible. Further study of surprising super-spirals like these will continue, likely including observations taken by NASA's James Webb Space Telescope scheduled for launch in 2021.
Tully-Fisher relation. The more luminous a galaxy is,
the faster it spins. Illustration: Astro533Fa10
These super-fast spinning galaxies are so fascinating!
I'm strongly reminded of the Tully-Fischer relation:
Wikipedia wrote:
In astronomy, the Tully–Fisher relation (TFR) is an empirical relationship between the mass or intrinsic luminosity of a spiral galaxy and its asymptotic rotation velocity or emission line width. It was first published in 1977 by astronomers R. Brent Tully and J. Richard Fisher.[1] The luminosity is calculated by multiplying the galaxy's apparent brightness by {\displaystyle 4\pi d^{2}}{\displaystyle 4\pi d^{2}}, where {\displaystyle d}d is its distance from us, and the spectral-line width is measured using long-slit spectroscopy.
So the more luminous a galaxy is, the faster it spins, which results in broad and smeared spectral lines. Presumably, too, a luminous galaxy is also a massive galaxy. So we can assume that fast-spinning galaxies are massive.
APOD Robot wrote:
It is therefore further hypothesized that their dark matter halos are so massive -- and their spins so fast -- that it is harder for them to form stars than regular spirals.
I get the idea of the massive dark matter halos, and I agree that the most massive galaxies rarely form a lot of stars. All right, but take a look at the middle galaxy in the bottom row, OGC 1304! This galaxy is among the fastest spinning galaxies known, and presumably it is very very massive, so it is not "allowed" to form a lot of stars. Well, OGC 1304 couldn't care less. Look at all the blue stuff all around it!
Click to play embedded YouTube video.
The middle galaxy in the top row is also relatively blue, but I agree that the other four galaxies are not churning out too many new stars. The two "end galaxies in the top row" are extremely elegant and beautiful. Why are they black and white? Were they photographed in (near) infrared light?
(By the way, I think the crazy kids in the carousel video are Danish.)
Ann
Re: APOD: Spiral Galaxies Spinning Super-Fast (2019 Nov 05)
Posted: Tue Nov 05, 2019 12:08 pm
by orin stepanek
When a skater pulls their arms in they spin spins faster! So to slow down their arms must come out! So; If the galaxies staro to separate their arms; they will probably slow down! IMHO
Re: APOD: Spiral Galaxies Spinning Super-Fast (2019 Nov 05)
Posted: Tue Nov 05, 2019 1:23 pm
by sillyworm 2
I'm fascinated by OGC 1403..the cosmic sunnyside up space egg.The central bulge appears massive.(unless that is a foreground star).Would love to see a clearer picture some day.
Re: APOD: Spiral Galaxies Spinning Super-Fast (2019 Nov 05)
Re: APOD: Spiral Galaxies Spinning Super-Fast (2019 Nov 05)
Posted: Tue Nov 05, 2019 2:34 pm
by Chris Peterson
orin stepanek wrote: ↑Tue Nov 05, 2019 12:08 pm
When a skater pulls their arms in they spin spins faster! So to slow down their arms must come out! So; If the galaxies staro to separate their arms; they will probably slow down! :mrgreen: IMHO
Well, these galaxies aren't expanding, so we're not going to see that. Also, keep in mind that a skater is a rigid body and a galaxy is not. While both are subject to conservation of momentum, the observed dynamics that result from it are somewhat different for the two.
Re: APOD: Spiral Galaxies Spinning Super-Fast (2019 Nov 05)
Posted: Tue Nov 05, 2019 3:08 pm
by TheOtherBruce
sillyworm 2 wrote: ↑Tue Nov 05, 2019 1:23 pm
I'm fascinated by OGC 1403..the cosmic sunnyside up space egg.The central bulge appears massive.(unless that is a foreground star).Would love to see a clearer picture some day.
I dunno, I can see another couple of possibilities here. It could be two similar spiral-ish galaxies in mid face-to-face collision, with the two nuclei still visibly separate. Or maybe one of them is something way in the background? Alternatively, it could be a stretched-out nearly edge on spiral, and the blue patch at lower left would be the end of a spiral arm; the speculative bit in between won't be visible unless we get a better picture. Lots of weird-looking stuff out there.
Do we have any guesstimates how far away they are? That might skew other figures one way or another.
Re: APOD: Spiral Galaxies Spinning Super-Fast (2019 Nov 05)
Posted: Tue Nov 05, 2019 3:25 pm
by tomatoherd
And it looks like, in the first two galaxies at least, there is some gravitational lensing around them. Meaning more mass. Something you don't notice on typical galaxy shots, only clusters. Am i wrong?
Re: APOD: Spiral Galaxies Spinning Super-Fast (2019 Nov 05)
Posted: Tue Nov 05, 2019 4:40 pm
by dlw
Is it possible to estimate a maximum angular velocity within these galaxies? Stating that "UGC 12591 spins at about 480 km/sec" doesn't give me a sense of how fast it is spinning.
Re: APOD: Spiral Galaxies Spinning Super-Fast (2019 Nov 05)
Hey... Tully & Fisher were fellow Astronomy grad students with me at the University of Maryland!
(They both got PhDs & I got a draft notice from Nixon. )
Art Neuendorffer
Thank you for serving, Art!!
Re: APOD: Spiral Galaxies Spinning Super-Fast (2019 Nov 05)
Posted: Tue Nov 05, 2019 5:02 pm
by Chris Peterson
dlw wrote: ↑Tue Nov 05, 2019 4:40 pm
Is it possible to estimate a maximum angular velocity within these galaxies? Stating that "UGC 12591 spins at about 480 km/sec" doesn't give me a sense of how fast it is spinning.
Well, the rotation speed changes with radial distance from the center. If we take the stated speeds to be the asymptotic speeds, that would be close to the speed at the outside edge of a galaxy. The paper places the size of most of these galaxies at around 200,000 ly diameter. So that means that they take about 300 million years to make a single rotation. Say an angular velocity of around one degree per million years.
Re: APOD: Spiral Galaxies Spinning Super-Fast (2019 Nov 05)
dlw wrote: ↑Tue Nov 05, 2019 4:40 pm
Is it possible to estimate a maximum angular velocity within these galaxies?
Stating that "UGC 12591 spins at about 480 km/sec" doesn't give me a sense of how fast it is spinning.
Well, the rotation speed changes with radial distance from the center. If we take the stated speeds to be the asymptotic speeds, that would be close to the speed at the outside edge of a galaxy. The paper places the size of most of these galaxies at around 200,000 ly diameter. So that means that they take about 300 million years to make a single rotation. Say an angular velocity of around one degree per million years.
dlw wrote: ↑Tue Nov 05, 2019 4:40 pm
Is it possible to estimate a maximum angular velocity within these galaxies?
Stating that "UGC 12591 spins at about 480 km/sec" doesn't give me a sense of how fast it is spinning.
Well, the rotation speed changes with radial distance from the center. If we take the stated speeds to be the asymptotic speeds, that would be close to the speed at the outside edge of a galaxy. The paper places the size of most of these galaxies at around 200,000 ly diameter. So that means that they take about 300 million years to make a single rotation. Say an angular velocity of around one degree per million years.
Typical star's rotation period 120 Myr
Spiral pattern rotation period 110–180 Myr
Bar pattern rotation period 50–60 Myr
Say a maximal angular velocity of around 6 degrees per million years...to keep Danish kids happy.
Very good point, Art. I, too, thought that a diameter of 200 000 light-years didn't sound like all that much for a humongous-sized galaxy.
Perhaps the luminous disk of the Milky Way really is about 100 000 light-years in diameter, but a low-luminosity halo or even outer disk makes our galaxy twice as wide? And possibly those super-large spiral galaxies also have low-luminosity outer disks that make them almost twice as big as they appear to be in our photographs of them?
Spiral Galaxies Spinning Super-Fast
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