Download High precision astrometry as a tool for Fundamental

Gravitation astrometric tests
in the external Solar System:
the QVADIS collaboration goals
M. Gai, A. Vecchiato
Istituto Nazionale di Astrofisica [INAF]
Osservatorio Astrofisico di Torino [OATo]
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High precision astrometry as a tool for Fundamental Physics
Micro-arcsec astrometry:
Current precision goals of astrometric infrastructures:
a few 10 µas, down to a few µas
1 arcsec (1)  5 µrad
1 micro-arcsec (1 µas)  5 prad
Reference cases:
• Gaia – space – visible range
• VLTI – ground – near infrared range
• VLBI – ground – radio range
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ESA mission – launched
Dec. 19th, 2013
Expected precision on
individual bright stars:
1030 µas
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Spacetime curvature around massive objects
Deflection angle [arcsec]
1.5
G: Newton’s
gravitational constant
1".74 at Solar limb  8.4 rad
GM
  1    2
c d
1
d: distance Sunobserver
1  cos
1  cos
M: solar mass
0.5
0
0
c: speed of light
: angular distance of
the source to the Sun
1
2
3
4
5
Distance from Sun centre [degs]
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Light deflection  Apparent variation of star position, related
to the gravitational field of the Sun
 ASTROMETRY
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Precision astrometry for Fundamental Physics – Gaia
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Precision astrometry for Fundamental Physics – AGP
 Talk
A = Apparent star position measurement
G = Testing gravitation in the solar system
1) Light deflection close to the Sun
2) High precision dynamics in Solar System
AGP:
Astrometric
Gravitation
Probe
P = Medium size space mission - ESA M4 (2014)
Design driver: light bending around the Sun @ μas fraction
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Quantum Vacuum behaviour vs. Gravitation
“Standard model”:
matter and anti-matter attract each other
Cosmological constant “catastrophe”
Vacuum energy not consistent with Solar System
dynamics (e.g. Mercury’s precession)?
Alternative theories:
matter and anti-matter repulse each other
[matter attracts matter, A-M attracts A-M]
Suggested e.g. from CPT symmetry
Effects may be tested by astrometry
[Villata, 2011; Hajdukovic, 2014; Kaplan et al., 2014; Villata, 2015]
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The Cosmological Constant trouble
Large “renormalisation” required
Cosmological constant  Dark Energy
Constraints from Solar System dynamics
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Polarisation of virtual pairs
External gravitation field attracts
particle and repulses anti-particle
Separation: ~ Compton wavelength
 Hajdukovic talk
Result: polarisation of virtual pairs
Effect similar to electromagnetic case
of charge in dielectric medium
Modified effective gravitation field
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Precision Astrometry in the Outer Solar System
Binary system as test particle:
Newtonian physics => Keplerian closed orbit
 Precession of binary
orbit in external field
Additional interactions => orbit perturbation,
in particular precession
Orbit no longer closed
Rotation of ellipse on its plane
Periastron precession
Larger displacement of apastron
Orbit monitoring  detection of external force
Requirement: Observation against field stars over several orbits
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The QVADIS Collaboration
Quantum Vacuum [effects] Astrometric Detection In the Solar system
•
International collaboration [Inst. Physics, Astrophysics,
Cosmology (ME); INAF-OATo (I)]
•
Experimental approach: check of deviation from Newtonian
dynamics on trans-Neptunian binaries
•
High precision narrow field astrometry from ground / space
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Study case: UX25
Trans-neptunian
binary system
≅ 6 mas/orbit
Newtonian precession from the Sun:
Estimated precession from vacuum polarisation:
Δ𝜔𝑞𝑣 ≃ 0.23 arcsec/orbit
[Hajdukovic, 2014, hal-00908554]
Cumulative effect on 5 years (~200 orbits): 46 arcsec
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Previous observations…
[M. E. Brown,
ApJL 2013]
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…and reconstructed orbit
Semi-major axis angular
amplitude: ~150 mas
System unresolved by
conventional telescopes
Faint visible magnitude:
• 20 mag primary
• 22 mag secondary
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Observing problem - I
Orbit variation over 5 years
Orbit
variation
(1D)
Unperturbed
orbit (1D)
Challenge: reliable µas astrometry
on faint objects, narrow field
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[Gai & Vecchiato, 2014,
arXiv:1406.3611]
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Observation setup
Multiple images taken over orbital
period along several orbits
Determination of positions and
velocity against field stars
Orbital fit: parameter estimate
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Observing problem - II
Small variation of observed vs. nominal
orbital positions over a few years
Requirement: few µas final precision
Small field (~10-20 arcmin) to have
several reference stars (e.g. from Gaia)
Simulation for ~100 µas precision on individual measurements
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Performance on 8 m telescope with adaptive optics
Observation in near
infrared bands
Photon noise, near
diffraction limited imaging
Exploit best instrument
performance
Feasible with 8 m AO telescope from ground – 10 nights/year
Best candidate:
James Webb Space Telescope (~2020) – 30 hours/year
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Third-body perturbations
Need for cross-check:
precession may be induced
by mass cluster in external
regions of the Solar system
Sun effect estimated 10
smaller than QV effect
[Hajdukovic 2014]
Measurement sensitive to any perturbation from known dynamics:
MOND, unknown objects, …
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Additional trans-neptunian binaries as candidates
After first detection, larger survey?
• confirm the effect
• identify dependency on system parameters
Dedicated space mission?
(55637) 2002 UX25
(136199) Eris and Dysnomia
(136108) Haumea, Hi'iaka, and Namaka
(50000) Quaoar and Weywot
(66652) Borasisi and Pabu
(42355) Typhon and Echidna
…
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Orbit disturbances from object shape
Celestial bodies are neither spheres nor point sources…
243 Ida
433 Eros
Vesta
951
Gaspra
[different viewpoints]
Tidal effects  orbit perturbations
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Example: Polyhedron-Polyhedron Systems
Chappaz, L., and Howell, K., "Bounded Motion near Binary Systems Comprised
of Small Irregular Bodies," AIAA/AAS Astrodynamics Specialist Conference,
San Diego, California, August 2014.
Near Earth Asteroid (NEA) 1999 KW4
Shape model [Ostro et al. 2006]:
primary and secondary
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Higher-Fidelity Dynamical Models: perturbed elliptical orbit
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Considerations on UX25 in-depth study
Long term monitoring with significant cadence sampling required:
-
measure time sequence of positions AND velocity
-
measure shape / brightness distribution
-
measure albedo / surface composition
-
deduce mass distribution
-
cross-check actual dynamics with high fidelity model predictions
Fundamental Physics result  confidence on system parameters
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Conclusions
High precision astrometry: tool for Fundamental Physics
Gravitation aspects of Quantum Vacuum need investigation
Quantum Vacuum polarisation effects close to state of the art
Experimental requirements of QV effects detection
Crucial constraints to e.g. MOND and local Dark Energy
Contributions to science case and implementation welcome!
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