The planet Earth is 26,800 ± 391 light years (i.e. ± 1.5%) from the center of the Milky Way galaxy.
The distance to the Galactic center R(0) is a fundamental parameter for understanding the Milky Way, because all observations of our Galaxy are made from our heliocentric reference point. The uncertainty in R(0) limits our knowledge of many aspects of the Milky Way, including its total mass and the relative mass of its major components, and any orbital parameters of stars employed in chemo-dynamical analyses.
While measurements of R(0) have been improving over a century, measurements in the past few years from a variety of methods still find a wide range of R(0) being somewhere within 8.0 to 8.5 kpc. The most precise measurements to date have to assume that Sgr A∗ is at rest at the Galactic center, which may not be the case.
In this paper, we use maps of the kinematics of stars in the Galactic bar derived from APOGEE DR17 and Gaia EDR3 data augmented with spectro-photometric distances from the astroNN neural-network method. These maps clearly display the minimum in the rotational velocity vT and the quadrupolar signature in radial velocity vR expected for stars orbiting in a bar. From the minimum in vT, we measure R(0) = 8.23 ± 0.12 kpc. We validate our measurement using realistic N-body simulations of the Milky Way.
We further measure the pattern speed of the bar to be Ω(bar)=40.08±1.78kms^−1kpc^−1. Because the bar forms out of the disk, its center is manifestly the barycenter of the bar+disc system and our measurement is therefore the most robust and accurate measurement of R(0) to date.
Henry W. Leung, et al. "A direct measurement of the distance to the Galactic center using the kinematics of bar stars" arXiv:2204.12551 (April 6, 2022).
5 comments:
btw
could a combination of MOND plus primordial black hole from Higgs inflation hypothesis
explain why both hypothesis seems correct but incomplete ?
MOND for galaxy rotation and primordial black hole for galaxies clusters CMB and gravitational lenses
tritonstation
April 28, 2022 at 5:00 pm
That may seem appealing, especially for clusters. For the CMB and structure formation, it could be problematic. If you make enough primordial black holes to do that, then there are enough of them to congregate in galaxies and act as dark matter. It is very hard to have it both ways.
Pretty much exactly what I have said.
may be this is better
How Cold Dark Matter Theory Explains Milgrom's Law
Manoj Kaplinghat (UChicago), Michael S. Turner (UChicago/FNAL)
Milgrom noticed the remarkable fact that the gravitational effect of dark matter in galaxies only becomes important where accelerations are less than about 10^{-8} cm s^{-2} ~ cH_0. This forms the basis for his Modified Newtonian Dynamics (MOND), an alternative to particle dark matter. However, any successful theory of galactic dynamics must account for Milgrom's Law. We show how Milgrom's Law comes about in the Cold Dark Matter (CDM) theory of structure formation.
Comments: Version accepted for publication in ApJ Letters; shortened intro; + discussion on collapsed baryon fraction
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:astro-ph/0107284
The origin of MOND acceleration and deep-MOND behavior from mass and energy cascade in dark matter flow
Zhijie Xu
The MOND paradigm is an empirical theory with modified gravity to reproduce many astronomical observations without invoking the dark matter hypothesis. Instead of falsifying the existence of dark matter, we propose that MOND is an effective theory naturally emerging from the long-range and collisionless nature of dark matter flow. It essentially describes the dynamics of baryonic mass suspended in fluctuating dark matter fluid. We first review the unique properties of self-gravitating collisionless dark matter flow (SG-CFD), followed by their implications in the origin of MOND theory. To maximize system entropy, the long-range interaction requires a broad size of halos to be formed. These halos facilitate an inverse mass and energy cascade from small to large mass scales that involves a constant rate of energy transfer ϵu=−4.6×10−7m2/s3. In addition to the velocity fluctuation with a typical scale u, the long-range interaction leads to a fluctuation in acceleration with a typical scale a0 that matches the value of critical MOND acceleration. The velocity and acceleration fluctuations in dark matter flow satisfy the equality ϵu=−a0u/(3π)2 such that a0 can be determined. A notable (unexplained) coincidence of cosmological constant Λ∝(a0/c)2 might point to a dark energy density proportional to acceleration fluctuation, i.e. ρvac∝a20/G. At z=0 with u=354.61km/s, a0=1.2×10−10m/s2 can be obtained. For given particle velocity vp, maximum entropy distributions developed from mass/energy cascade lead to a particle kinetic energy ϵk∝vp at small acceleration a0. Combining this with the constant rate of energy transfer ϵu, both regular Newtonian dynamics and deep-MOND behavior can be fully recovered.
Comments: 20 pages, 8 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); Fluid Dynamics (physics.flu-dyn)
Cite as: arXiv:2203.05606 [astro-ph.CO]
It is very hard to have it both ways.
andrew said...
Pretty much exactly what I have said.
MOND failure is in galaxies clusters CMB and gravitational lenses
that need to be fixed
besides deur, how to fix this
Not CMB. Not gravitational lenses.
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