Image of the Week

Testing CDM and geometry-driven Milky Way rotation Curve Models

 

A plot of the Gaia Milky Way rotation curve and fitted models is shown in this figure, where the azimuthal velocity profile of the Milky Way as derived from a sample of disc tracers from Gaia DR2 is given. Image credit: M.Crosta, M.Giammaria, M.G.Lattanzi, E.Poggio MNRAS, Volume 496, Issue 2, August 2020.

 

The work "on testing CDM and geometry-driven Milky Way rotation curve models with Gaia DR2" demonstrates for the first time, thanks to the large scale, highly accurate mapping of stellar distances and velocities enabled by the ESA Gaia mission, that the observed flatness of the Milky Way rotation curve can have a general relativistic origin, not predictable from Newtonian gravity.

The study suggests that the underlying geometry drives the stellar velocities in the plane of our Galaxy away from its center consistently with Einstein’s theory. Indeed, given the gravitational sources and an underlying geometry, “space tells matter how to move, matter tells space how to curve” (J.A. Wheeler). In this respect, geometry, as manifestation of gravity, would tackle the gravitational properties of Dark Matter (DM).

The investigation also shows that one of Einstein’s equations provides the necessary baryonic matter density in a self-consistent way. Then, no additional extra matter is required, while the relativistic velocity profile results statistically indistinguishable from its state-of-the-art DM-based analogue, introduced to account for the gap between the observed rotation curve and the expected Newtonian velocities, after the historical observations of Zwicky and Vera Rubin. This dark matter is supposed to reside mostly in the Galactic halo, whereas the relativistic dragging velocity in the disk can effectively compensate for its absence.

By utilizing Gaia DR2 products (parallaxes to better than 20% and the complete set of proper motions and line-of-sight velocities) and the complement of 2MASS photometry, we were able to select a very homogenous sample of 5602 disk stars (5277 UMS stars and 325 classical type I Cepheids), and then reconstruct the kinematics of the axisymmetric part of the Galactic potential over a large range (from 5 to 16 kpc) of galactocentric distances.

Two models, one general relativity and a DM-based analogue, were fit to these unprecedented Galactic rotation curve data, and the results have shown for the first time that a general relativity model is able to represent the experimental data with a quality in all similar to that of a traditional model based on Newtonian dynamics and a dark matter halo.

In the light of these results, future Galactic model should be developed consistently with the data delivered by Gaia. Indeed, it was crucial that we correctly framed the velocity measurement made by the observer at rest with the Solar System (BCRS) and the one at rest with the center of the Galaxy. Contrary to classical astronomy, the measurement process in general relativity depends on the underlying geometry and such a velocity turns out to be proportional to the off-diagonal term of the metric related to the gravitational dragging.

The only general relativity model that allowed us to apply the above first principles was a (simplified) general relativistic dust model, axisymmetric and stationary. For this case an appropriate velocity profile was proposed in recent years by Balasin and Grummiller (2008). Despite some inadequacies and incompleteness (e.g., it cannot be extended, as is, to the inner regions of the Milky Way), this model has proven to be quite useful for demonstrating the relativistic nature of the Gaia-mapped rotation curve from within our Milky Way, allowing also to estimate the (external) radial size of the Galactic bulge and the disc thickness at radial distances R>4 kpc.

These encouraging initial results call for the thorough use of Einstein’s theory in the years to come, and state the need to develop more complex relativistic galactic “geometries” that can take into proper account the various structures of the Galaxy. This also in anticipation of the incoming and increasingly accurate new Gaia data releases and, possibly, of other observations targeting the Galaxy central regions. Finally, a proper general relativity representation of the Milky Way, as depicted by the Gaia-like relativistic observer, can help putting to test, at the Galactic scale, the predictions of any cosmological model of our Galaxy.

This study resulted from the research activities of the INAF-OATo team working on gravitational astrometry and its testing at the local and Galactic scale. This is a multidisciplinary group of scientists bringing together crucial expertise that has helped “gluing” together critical aspects, from theory to testing. Also, this work is part of the research activities of M. Giammaria toward his Phd in Physics with the University of Torino (M. Crosta and M. G. Lattanzi advisors). The program is funded by INAF and supported by ASI through contract 2014-025-R.1.2015.

 

Credits: M. Crosta, M. Giammaria,M.G. Lattanzi, E. Poggio

[Published: 16/07/2020]

 

Image of the Week Archive

2020
29/10: Gaia EDR3 passbands
15/10: Star clusters are only the tip of the iceberg
04/09: Discovery of a year long superoutburst in a white dwarf binary
12/08: First calibrated XP spectra
22/07: Gaia and the size of the Solar System
16/07: Testing CDM and geometry-driven Milky Way rotation Curve Models
30/06: Gaia's impact on Solar system science
14/05: Machine-learning techniques reveal hundreds of open clusters in Gaia data
20/03: The chemical trace of Galactic stellar populations as seen by Gaia
09/01: Discovery of a new star cluster: Price-Whelan1
08/01: Largest ever seen gaseous structure in our Galaxy
2019
20/12: The lost stars of the Hyades
06/12: Do we see a dark-matter like effect in globular clusters?
12/11: Hypervelocity star ejected from a supermassive black hole
17/09: Instrument Development Award
08/08: 30th anniversary of Hipparcos
17/07: Whitehead Eclipse Avoidance Manoeuvre
28/06: Following up on Gaia Solar System Objects
19/06: News from the Gaia Archive
29/05: Spectroscopic variability of emission lines stars with Gaia
24/05: Evidence of new magnetic transitions in late-type stars
03/05: Atmospheric dynamics of AGB stars revealed by Gaia
25/04: Geographic contributions to DPAC
22/04: omega Centauri's lost stars
18/04: 53rd ESLAB symposium "the Gaia universe"
18/02: A river of stars
2018
21/12: Sonification of Gaia data
18/12: Gaia captures a rare FU Ori outburst
12/12: Changes in the DPAC Executive
26/11:New Very Low Mass dwarfs in Gaia data
19/11: Hypervelocity White Dwarfs in Gaia data
15/11: Hunting evolved carbon stars with Gaia RP spectra
13/11: Gaia catches the movement of the tiny galaxies surrounding the Milky Way
06/11: Secrets of the "wild duck" cluster revealed
12/10: 25 years since the initial GAIA proposal
09/10: 3rd Gaia DPAC Consortium Meeting
30/09: A new panoramic sky map of the Milky Way's Stellar Streams
25/09: Plausible home stars for interstellar object 'Oumuamua
11/09: Impressions from the IAU General Assembly
30/06: Asteroids in Gaia Data
14/06: Mapping and visualising Gaia DR2

25/04: In-depth stories on Gaia DR2

14/04: Gaia tops one trillion observations
16/03: Gaia DR2 Passbands
27/02: Triton observation campaign
11/02: Gaia Women In Science
29/01: Following-up on Gaia
2017
19/12: 4th launch anniversary
24/11: Gaia-GOSA service
27/10: German Gaia stamp in the making
19/10: Hertzsprung-russell diagram using Gaia DR1
05/10: Updated prediction to the Triton occultation campaign
04/10: 1:1 Gaia model arrives at ESAC
31/08: Close stellar encounters from the first Gaia data release
16/08: Preliminary view of the Gaia sky in colour
07/07: Chariklo stellar occultation follow-up
24/04: Gaia reveals the composition of asteroids
20/04: Extra-galactic observations with Gaia
10/04: How faint are the faintest Gaia stars?
24/03: Pulsating stars to study Galactic structures
09/02: Known exoplanetary transits in Gaia data
31/01: Successful second DPAC Consortium Meeting
2016
23/12: Interactive and statistical visualisation of Gaia DR1 with vaex
16/12: Standard uncertainties for the photometric data (in GDR1)
25/11: Signature of the rotation of the galactic bar uncovered
15/11: Successful first DR1 Workshop
27/10: Microlensing Follow-Up
21/10: Asteroid Occultation
16/09: First DR1 results
14/09: Pluto Stellar Occultation
15/06: Happy Birthday, DPAC!
10/06: 1000th run of the Initial Data Treatment system
04/05: Complementing Gaia observations of the densest sky regions
22/04: A window to Gaia - the focal plane
05/04: Hipparcos interactive data access tool
24/03: Gaia spots a sunspot
29/02: Gaia sees exploding stars next door
11/02: A new heart for the Gaia Object Generator
04/02: Searching for solar siblings with Gaia
28/01: Globular cluster colour-magnitude diagrams
21/01: Gaia resolving power estimated with Pluto and Charon
12/01: 100th First-Look Weekly Report
06/01: Gaia intersects a Perseid meteoroid
2015
18/12: Tales of two clusters retold by Gaia
11/11: Lunar transit temperature plots
06/11: Gaia's sensors scan a lunar transit
03/11: Celebrity comet spotted among Gaia's stars
09/10: The SB2 stars as seen by Gaia's RVS
02/10: The colour of Gaia's eyes
24/09: Estimating distances from parallaxes
18/09: Gaia orbit reconstruction
31/07: Asteroids all around
17/07: Gaia satellite and amateur astronomers spot one in a billion star
03/07: Counting stars with Gaia
01/07: Avionics Model test bench arrives at ESOC
28/05: Short period/faint magnitude Cepheids in the Large Magellanic Cloud
19/05: Visualising Gaia Photometric Science Alerts
09/04: Gaia honours Einstein by observing his cross
02/04: 1 April - First Look Scientists play practical joke
05/03: RR Lyrae stars in the Large Magellanic Cloud as seen by Gaia
26/02: First Gaia BP/RP deblended spectra
19/02: 13 months of GBOT Gaia observations
12/02: Added Value Interface Portal for Gaia
04/02: Gaia's potential for the discovery of circumbinary planets
26/01: DIBs in three hot stars as seen by Gaia's RVS
15/01: The Tycho-Gaia Astrometric Solution
06/01: Close encounters of the stellar kind
2014
12/12: Gaia detects microlensing event
05/12: Cat's Eye Nebula as seen by Gaia
01/12: BFOSC observation of Gaia at L2
24/11: Gaia spectra of six stars
13/11: Omega Centauri as seen by Gaia
02/10: RVS Data Processing
12/09: Gaia discovers first supernova
04/08: Gaia flag arrives at ESAC
29/07: Gaia handover
15/07: Eclipsing binaries
03/07: Asteroids at the "photo finish"
19/06: Calibration image III - Messier 51
05/06: First Gaia BP/RP and RVS spectra
02/06: Sky coverage of Gaia during commissioning
03/04: Gaia source detection
21/02: Sky-background false detections in the sky mapper
14/02: Gaia calibration images II
06/02: Gaia calibration image I
28/01: Gaia telescope light path
17/01: First star shines for Gaia
14/01: Radiation Campaign #4
06/01: Asteroid detection by Gaia
2013
17/12: Gaia in the gantry
12/12: The sky in G magnitude
05/12: Pre-launch release of spectrophotometric standard stars
28/11: From one to one billion pixels
21/11: The Hipparcos all-sky map
15/10: Gaia Sunshield Deployment Test
08/10: Initial Gaia Source List
17/09: CU1 Operations Workshop
11/09: Apsis
26/08: Gaia arrival in French Guiana
20/08: Gaia cartoons
11/07: Model Soyuz Fregat video
01/07: Acoustic Testing
21/06: SOVT
03/06: CU4 meeting #15
04/04: DPCC (CNES) 
26/03: Gaia artist impression 
11/02: Gaia payload testing  
04/01: Space flyby with Gaia-like data
2012
10/12: DPAC OR#2. Testing with Planck
05/11: Galaxy detection with Gaia
09/10: Plot of part of the GUMS-10 catalogue
23/07: "Gaia" meets at Gaia
29/06: The Sky as seen by Gaia
31/05: Panorama of BAM clean room
29/03: GREAT school results
12/03: Scanning-law movie
21/02: Astrometric microlensing and Gaia
03/02: BAM with PMTS
12/01: FPA with all the CCDs and WFSs
2011
14/12: Deployable sunshield
10/11: Earth Trojan search
21/10: First Soyuz liftoff from the French Guiana
20/09: Fast 2D image reconstruction algorithm
05/09: RVS OMA
10/08: 3D distribution of the Gaia catalogue
13/07: Dynamical Attitude Model
22/06: Gaia's view of open clusters
27/05: Accuracy of the stellar transverse velocity
13/05: Vibration test of BAM mirrors
18/04: L. Lindegren, Dr. Honoris Causa of the Observatory of Paris
19/01: Detectability of stars close to Jupiter
05/01: Delivery of the WFS flight models
2010
21/12: The 100th member of CU3
17/11: Nano-JASMINE and AGIS
27/10: Eclipsing binary light curves fitted with DPAC code
13/10: Gaia broad band photometry
28/09: Measuring stellar parameters and interstellar extinction
14/09: M1 mirror
27/08: Quest for the Sun's siblings
 
Please note: Entries from the period 2003-2010 are available in this PDF document.