Dark matter is putting the brakes on our Milky Way galaxy's spin

[Admin]

The rotation of the Milky Way bar has slowed by almost a quarter since its formation.

Dark matter is putting the brakes on our Milky Way galaxy's spin : Read more

 

[rod]

The article says, "These new findings not only shed light on the rotation of the Milky Way but also provide an insight into the nature of one of the most elusive materials in the universe — dark matter."

Okay, this report supports DM, now read this new report. No DM in this galaxy. 'Hubble data confirms galaxies lacking dark matter', https://phys.org/news/2021-06-hubble-galaxies-lacking-dark.html, "The most accurate distance measurement yet of ultra-diffuse galaxy (UDG) NGC1052-DF2 (DF2) confirms beyond any shadow of a doubt that it is lacking in dark matter..."

ref - A Tip of the Red Giant Branch Distance of 22.1 ± 1.2 Mpc to the Dark Matter Deficient Galaxy NGC 1052–DF2 from 40 Orbits of Hubble Space Telescope Imaging, https://iopscience.iop.org/article/10.3847/2041-8213/ac0335, 09-June-2021.

DM supported in one report, another shows up where DM is not supported

 

[Catastrophe]

Rod, sorry to raise this question again (in a different context).
How would one determine the axis of rotation of a galaxy? That is spin (as stated) as opposed to rotation. Rotation = orbiting, I understand, but not spin (defined as rotation about an axis).

Cat

 

[rod]

Cat good question. My understanding, revolution is for planets orbiting a star, rotation is for spin on an axis like the Sun or planets in our solar system. The space.com report cites https://academic.oup.com/mnras/article/505/2/2412/6237521

Looks like metallicity and LSR are used too along with Gaia astrometry. The LSR can be read about here, Earth faster, closer to black hole in new map of galaxy, https://phys.org/news/2020-11-earth-faster-closer-black-hole.html, Nov-2020. Another report, Local standard of rest based on Gaia DR2 catalog, https://ui.adsabs.harvard.edu/abs/2019RAA....19...68D/abstract, May-2019. "The local standard of rest (LSR) provides a reference framework for studies of Galactic kinematics. Determination of the LSR corresponds to the measurement of solar peculiar motion, which is under debate due to the fact that different methods and samples have been used. Adopting the astrometric data and line-of-sight velocities of main sequence stars from Gaia DR2, we present a detailed analytical study of stellar kinematics in the solar neighborhood."

The paper indicates scaling using metallicity in star observations and comments about the LSR too for determining bar *rotation*.

 

[Catastrophe]

Rod, if you check back to my dictionary definitions , if one uses the word spin for single bodies there is no problem. Rotate definitely can mean either spin or orbit, so is best avoided. Orbit can only mean one body rotating around another. In this case, you can, and usually do, have both one body orbiting another, and both bodies spinning on their own axes. You can say correctly (but ambiguously) one body is rotating around another and both bodies can be rotating about their own axes.

Cat

Where moments of inertia thread post #13

P.S. by (but ambiguously) I meant that rotating is used in both senses.

 

[sam85geo]

I didn't know that the Milky Way was a barred spiral. But I'm not prejudice. So if there is Dark Matter in the Milky Way, it's purported to have slowed down the rotation of the bar portion by ~24%. On the other hand, if there is no Dark Matter in the Milky Way, then what could have slowed the bar's rotation, given that the measurements and method were accurate? As a follow on, what would such a slowing portend? Any speculations and additional references are welcome. Thanks.

 

[Catastrophe]

I don't know if this helps directly, but it is certainly very very relevant to the cyclic models, which, some might suggest, could suffer from the reverse sequence from maximum extent to BB. Well, here is a possible answer from an article "The Great Dark Energy Survey" by Keith Cooper (Ed Astronomy Now), ibid, July 2021 (is that up to date?):

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"A cosmological constant would see space expand into infinity - as space expands, new space is created, and each bit of new space would share the same value of dark energy, so the acceleration of cosmic expansion would ramp up exponentially. This could potentially lead to a catastrophic 'Big Rip', where dark energy tears the Universe apart. A scalar field that varies with space and tie would, however, mean that all best are off - the Universe could keep expanding, but equally possible is the chance that dark energy would then weaken, slowing or even reversing the expansion and causing a Big Crunch' in the far future."
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Cat