Fundamental
Physics
and
Astrophysics
using
Pulsars and the SKA
Jim Cordes
Cornell U.
Vicky Kaspi
McGill U.
Michael Kramer
Jodrell Bank
Pulsar Science Highlights
Key Science:
• Strong-field Tests of Gravity
•Was Einstein Right?
•Cosmic Censorship, “No-Hair” Theorem
• Cosmic Gravitational Wave Background
Variety of Other Major Astrophysical Topics:
•Milky Way Structure, ISM
•Intergalactic Medium
•Relativistic Plasma Physics
•Extreme Densities
•Extreme Magnetic Fields
Pulsars…
• embody physics of the EXTREME
– surface speed ~0.1c
– 10x nuclear density in centre
– some have B > Bq = 4.4 x 1013 G
– Voltage drops ~ 1012 volts
– FEM = 109Fg = 1011FgEarth
– Tsurf ~ million K
• …relativistic plasma physics in action
• …probes of turbulent and magnetized ISM
• …precision tools, e.g.
- Period of B1937+21:
P = 0.00155780649243270.0000000000000004 s
- Orbital eccentricity of J1012+5307: e<0.0000008
Noted GR Laboratories
Hulse & Taylor (1974)
Weisberg & Taylor (priv. comm)
• Orbit shrinks every day by 1cm
• Confirmation of existence of gravitational waves
First Double Pulsar!
Lyne et al.(2004)
• Pb=2.4 hrs, d/dt=17 deg/yr
• MA=1.337(5)M, MB=1.250(5)M
Testing GR:
s obs
 1.000  0.002
exp
s
Kramer et al.(2004)
Was Einstein right?
General Relativity
•
•
•
•
vs
Alternative Theories
Strong Equivalence Principle
Violation of Lorentz-Invariance
Violation of Positional Invariance
Violation of Conservation Laws etc.
Albert Einstein
Solar System tests provide constraints
…but only in weak field!
v
 10 3
 
 c  orbit
 PSR  0.15
 BH  0.5
No test of any theory of gravity is
complete, if only done in solar system,
i.e. strong field limit and radiative aspects
need to be tested, too!
v
 10  4
 
 c  orbit
 Sun  10 6
 Earth  10 10
 Moon  10 11
 This is and will be done best with radio pulsars!
Was Einstein right?
General Relativity
•
•
•
•
vs
Alternative Theories
Strong Equivalence Principle
Violation of Lorentz-Invariance
Violation of Positional Invariance
Violation of Conservation Laws etc.
Albert Einstein
Binary Pulsars: • Clean strong-field tests, incl.
• Shapiro delays
• Gravitational Radiation
• Geodetic Precession
So far:
General Relativity has passed
all tests with flying colours!
Exploration of Black Holes
Compact
PSR Binaries
We will probe BH properties with pulsars and SKA:
- precise measurements
- no assumptions about EoS or accretion physics
- test masses well separated, not deformed
Black Hole properties
spin and quadrupole moment:
•Astrophysical black holes are expected to rotate
c S

2
GM
4
c Q
q 2 3
G M
S = angular momentum
Q = quadrupole moment
• Result is relativistic & classical spin-orbit coupling
• Visible as a precession of the orbit:
Measure higher order derivatives of secular
changes in semi-major axis and longitude of
periastron (relativistic) or transient TOA
perturbations (classical)
• Not easy! It is not possible today!
• Requires SKA sensitivity!
Cosmic Censorship & No-Hair
• For BH-like companions to pulsars, we will
measure spin precisely
• In GR, for Kerr-BH we expect:
But if we measure
 1
 > 1  Event Horizon vanishes
 Naked singularity!
GR is wrong or Censorship Conjecture violated!
Cosmic Censorship & No-Hair
• For BH-like companions to pulsars, we will
measure spin precisely
• In GR, for Kerr-BH we expect:
But if we measure
 1
 > 1  Event Horizon vanishes
 Naked singularity!
GR is wrong or Censorship Conjecture violated!
If we measure for quadrupole
q  
2
either GR is wrong, i.e. “No-Hair” theorem violated!
or we have discovered a new kind of object,
e.g. a quark star
Galactic Census with the SKA
• Blind survey for pulsars will discover ~10,000-20,000,
practically complete census!
• Find all observable PSR-BH systems!
• High-Precision timing of discovered binary and
millisecond pulsars
• “Find them!”
• “Time them!”
• “VLBI them!”
Benefiting from SKA twice:
• Unique sensitivity: many pulsars, ~10,000-20,000
incl. of
many
rare
Not just a continuation
what
hassystems!
been done before
• Unique timing
precision and
beams!
- Complete
new multiple
quality of
science possible!
Pulsar Astrophysics with SKA
Wide range of applications:
• Galactic probes: Interstellar medium/magnetic field
Magnetic field
Star formation history
Dynamics
Population via distances (ISM, VLBI)
Electron
distribution
Movement in potential
Galactic Centre
Pulsar Astrophysics with SKA
Wide range of applications:
• Galactic probes
• Extragalactic pulsars: Missing Baryon Problem
Formation & Population
Turbulent magnetized IGM
Search nearby galaxies!
Giant pulses
Reach the local group!
Pulsar Astrophysics with SKA
Wide range of applications:
• Galactic probes
• Extragalactic pulsars
• Relativistic plasma physics: Emission Processes
Pulsar Wind Nebulae
Magnetospheric Structure
Pulsar Astrophysics with SKA
Wide range of applications:
•
•
•
•
Galactic probes
Extragalactic pulsars
Relativistic plasma physics
Extreme Matter Physics: Ultra-strong B-fields
Equation-of-State
Physics of Core collapse
Pulsar Astrophysics with SKA
Wide range of applications:
•
•
•
•
•
Galactic probes
Extragalactic pulsars
Relativistic plasma physics
Extreme Dense Matter Physics
Multi-wavelength studies: Photonic windows
Non-photonic windows
Pulsar Astrophysics with SKA
Wide range of applications:
•
•
•
•
•
•
Holy Grail: PSR-BH
Galactic probes
Extragalactic pulsars
Relativistic plasma physics
Extreme Dense Matter Physics
Multi-wavelength studies
Exotic systems: planets
pulsar/MS binaries
millisecond pulsars
relativistic binaries
double pulsars
PSR-BH systems
Double Pulsars
Planets
Cosmological Gravitational Wave Background
• stochastic gravitational wave background
expected on theoretical grounds
Possible Sources:
• Inflation
• String cosmology
• Cosmic strings
• phase transitions
h GW ( f ) ~ const.
2
0
and also: merging massive BH binaries
in early galaxy evolution
h02GW ( f )  f 2 / 3
Cosmological Gravitational Wave Background
• Pulsars discovered in Galactic Census also
provide network of arms of a huge
cosmic gravitational wave detector
PTA:
Pulsar
Timing
Array
• Perturbation in
space-time can be
detected in timing
residuals
• Sensitivity: dimensionless strain
hc ( f ) ~
 TOA
T
Cosmological Gravitational Wave Background
CMB
Pulsars
Advanced
LISA LIGO
PTA limit:
h GW ( f ) ~ 
2
0
2
TOA
f
4
Further by correlation:
1 / N PSR
Improvement: 104!
Spectral range: nHz
only accessible with SKA!
complementary to
LISA, LIGO & CMB
Technical Requirements for Probing
Fundamental Physics with the SKA
• Blind Searching
– Periodicity searches
– Giant-pulse searches
• Pulse timing of discovered pulsars
• Astrometry using VLB baselines
• Other:
• scintillation studies
• single pulse polarimetry
• synoptic studies (eclipsing systems, magnetospheric
physics, etc)
Blind Searching
• Traditional: periodic dispersed pulses and single
dispersed pulses
• Extension: signals with greater time-frequency
complexity than known pulsar signals (flare stars,
GRBs, SETI, …)
• Search as large a field of view as possible to
maximize throughput and to allow multiple passes
for transient objects
• Search domains:
–
–
–
–
–
Galactic plane (e.g. |b| < 5°)
“Galactic halo” MSPs and binary pulsars
Galactic center star cluster
Nearby galaxies (periodic and single-pulse searches)
Virgo cluster galaxies (giant pulse searches)
Blind Searching for
Pulsars
Implications for SKA requirements:
– Frequency range
– Antenna configuration
– Antenna connectivity and signal transport
– Real-time signal processing
– Quasi-real-time and long-term data management
Blind Searching for
Pulsars
Implications for SKA requirements:
– Frequency range
• 0.3 to 2 GHz for most Galactic and extragalactic directions
• > 12 GHz for the Galactic center
– Antenna configuration
• compact core with significant fraction of the collecting area
– Antenna connectivity and signal transport
• Beamforming/correlation of all directly-connected antennas with ~64 s
dump times and ~1024 spectral channels across ~20% bandwidth
– Real-time signal processing
• RFI excision
• Portion of pulsar search algorithm on data stream from each pixel
– Quasi-real-time and long-term data management
• Remainder of pulsar search algorithm
• Crosschecks between beams, etc. to further discriminate RFI and celestial
signals
• Archival of low-and-high-level data products
Pulsar detectability
with the SKA for GC
pulsars and
extragalactic pulsars
High frequencies are
needed for searches of
the Galactic Center
owing to intense radio
wave scattering
Blind Searching: Field of
View
2
To search  deg with tbeam hr/beam requires:
T = 104 hr [tbeam/ 1 hr] [/104 deg2] / [FOV/1 deg2]
Sensitivity ~ 35 times upcoming Arecibo ALFA surveys
if full SKA sensitivity is available for searching (it won’t)
Need to maximize the searchable FOV and collecting
area for blind searching
 Need a compact core with as much collecting area as
possible (fc=fraction in core) involving direct correlation
of antennas (no stations)
Primary beam &
synthesized beams
Blind surveys require full
FOV sampling
Blind Surveys with SKA
(pulsars, transients, ETI)
• Number of pixels needed to
cover FOV:
Npix~(bmax/D)2 ~104-109
• Number of operations
Nops~ petaops/s
• Post processing per beam:
single-pulse and periodicity
analysis
Dedisperse (~1024 trial DM
values) + FFT + harmonic sum (+
orbital searches + RFI excision)
• Correlation is more efficient
than direct beam formation
• Requires signal transport of
individual antennas to correlator
≥104 beams needed
for full-FOV sampling
SKA pulsar survey
64 s samples
1024 channels
600 s per beam
~104 psr’s
Pulse Timing
•
•
•
•
Can never have too much timing precision!
TOA  100 ns is desirable
Radiometer noise: TOA  W  SEFD
Systematics:
• Pulse phase jitter: TOA  fjW(P/T)1/2
• Scattering-induced errors: DM variations, variable
pulse broadening: TOA(DM)  -2, TOA(PB) -4
• Pulse polarization + calibration errors  pulse shape
changes  TOA errors
– Need Stokes total I precision  1% or voltage
polarization purity to better than 10-4 (-40 dB)
Pulse Timing
Multiple beaming and multiple FOV:
– Follow up timing required to varying
degrees on the ~ 2x104 pulsars
discoverable with SKA
• Spin parameters, DM and initial astrometry
• Orbital evolution for relativistic binaries
• Gravitational wave detection using MSPs
– Each deg2 will contain only a few pulsars
 efficient timing requires large solidangle coverage (lower frequencies,
subarrays, wide intrinsic FOV, or multiple
FOVs)
The need for multiplexed timing:
VLB Astrometry
• Proper motions and parallaxes for objects
across the Galaxy  monitoring programs
over ~ 2 yr/pulsar
• Optimize steep pulsar spectra against dependence of ionospheric and tropospheric
and interstellar phase perturbations ( 2 to
8 GHz)
• In-beam calibrators (available for all fields
with SKA)
• 10% of A/T on transcontinental baselines
implies 20 times greater sensitivity over
existing dedicated VLB arrays
SKA Specifications Summary
for Fundamental Physics
from Pulsars
Required Specification
Topic
Searching
t
(s)
A/T
(m2/K)
max
(GHz)
Configuration
FOV
Sampling
Polarization
50
2x104 fc
2.5
15 (GC)
Core with large
fc
full
Total
Intensity
Timing
1
2x104
15
Non-critical if
phasable
Astrometry
(VLB)
200
>2x103
8
Intercontinental
baselines
100
beams/deg2
~ 3 beams
Full
Stokes;
-40 dB
isolation
Total
Intensity
The road to the SKA:
• ALFA
• Prototypes: ATA, LAR, EMBRACE, SKAMP
• International SKA demonstrator
• Timing:
Arecibo-like precision
High-frequency surveys
Parkes Multibeam
ALFA
?
SKA
• Searching:
2000-5000 pulsars
Is this all we need?
Projected Discoveries
Today Future
Projected Discoveries
Millisecond Pulsars
Today Future
Relativistic Binaries
Today Future
only 6!
SKA
SKA
Work with SKA prototypes
• Searches:
- Chances to find ~200-400 MSPs
- Location of demonstrators is important!!
- For PSR-BH we need to look at GC & Cluster
but one may be lucky
Work with SKA prototypes
• Searches:
- Chances to find ~200-400 MSPs
- Location of demonstrators is important!!
- For PSR-BH we need to look at GC & Cluster
but one may be lucky
• Timing:
- Some improvement for GW-limit
Gravitational Wave Background
•With SKA about
104 improvement
Gravitational Wave Background
•With prototype we
may detect massive
BH binaries
•We will not set
very stringent limit
on strings etc.
Work with SKA prototypes
• Searches:
- Chances to find ~200-400 MSPs
- Location of demonstrators is important!!
- For PSR-BH we need to look at GC & Cluster
but one may be lucky
• Timing:
- Some improvement for GW-limit
Work with SKA prototypes
• Searches:
- Chances to find ~200-400 MSPs
- Location of demonstrators is important!!
- For PSR-BH we need to look at GC & Cluster
but one may be lucky
• Timing:
- Some improvement for GW-limit
- IF we found PSR/BH,
extremely unlikely to measure BH spin
- If measurement, about few  10%
Timing of PSR/BH
SKA Demonstrator
d2x/dt2
Fractional Error
dx/dt
sin(i)
γ
dPb/dt
ώ
Timing precision of essential Post-Keplerian parms.
Timing of PSR/BH
SKA
SKA Demonstrator
d2x/dt2
sin(i)
γ
dPb/dt
Fractional Error
Fractional Error
dx/dt
ώ
Timing precision of essential Post-Keplerian parms.
Work with SKA prototypes
• Searches:
- Chances to find ~200-400 MSPs
- Location of demonstrators is important!!
- For PSR-BH we need to look at GC & Cluster
but one may be lucky
• Timing:
- Some improvement for GW-limit
- IF we found PSR/BH,
extremely unlikely to measure BH spin
- If measurement, about few  10%
- Impossible to measure BH quadrupole moment
Timing of PSR/BH
• Need to detect transient signals with amplitude of ~10ns-1s
• Periodically occurring at periastron
• Need instantaneous sensitivity to resolve it
Wex & Kopeikin (1999):
• We can average data of different orbits: e.g. for 30 ns signal
we need to average about 1000 TOAs (per orb. phase)
 with only 2 TOAs per day, SKA needs less than 1.5 years
• With SKA demonstrator, we need 14 years
Work with SKA prototypes
• Searches:
- Chances to find ~200-400 MSPs
- Location of demonstrators is important!!
- For PSR-BH we need to look at GC & Cluster
but one may be lucky
• Timing:
- Some improvement for GW-limit
- IF we found PSR/BH,
extremely unlikely to measure BH spin
- If measurement, about few  10%
- Impossible to measure BH quadrupole moment
Demonstrator is not good enough!
We need the REAL SKA!
The SKA Pulsar Sky
 Was Einstein right? – Fundamental question in physics &
quest for quantum gravity!
 Unique to radio astronomy - Only possible with the SKA!
 It excites public and community – e.g. “Quarks & Cosmos” &
>1 Million websites