Scott A. Hughes, MIT

1
Gravitational waves from cosmological binary
black holes A tool for studying the growth of
structure in the universe.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
2
Storyline
The growth of structure/galaxies provides a
natural mechanism to produce binary black holes
...
... the gravitational waves emitted by these
binaries are radiated at frequencies in which
LISA is most sensitive ...
... measurement of these waves provides a rich
set of data on the emitting binary.
Measuring these waves will enable us to directly
probe the cosmological growth of black holes and
structure in the universe!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
3
A brief history of galaxies
Cosmic microwave background gives first glimpse
of the universes largest structures
Spectrum confirms that universes matter is
mostly dark Ratio of acoustic peaks requires
roughly 5 parts dark matter for 1 part normal
matter.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
4
A brief history of galaxies
Use CMB to specify initial data for overdensity
relative to mean matter field in early universe.
Gravity grows overdensities A slight overdensity
at z 1100 will become progressively more dense
as that region attracts more matter to itself.
Initial overdensity is tiny (d?/? 10-6), can
treat evolution with a simple linear
theory (Zeldovich 1970, AA, 5, 84)
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
5
A brief history of galaxies
Evolution of density inhomogeneities
z 18.3
d?/? 1 Linear evolution of density field no
longer accurate.
Credit The VIRGO Cosmological N-body Project
http//www.mpa-garching.mpg.de/galform/virgo
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
6
A brief history of galaxies
Evolution of density inhomogeneities
z 5.7
Numerical calculations allow tracking of growth
through nonlinear regime.
Credit The VIRGO Cosmological N-body Project
http//www.mpa-garching.mpg.de/galform/virgo
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
7
A brief history of galaxies
Evolution of density inhomogeneities
z 1.4
Numerical calculations allow tracking of growth
through nonlinear regime.
Credit The VIRGO Cosmological N-body Project
http//www.mpa-garching.mpg.de/galform/virgo
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
8
A brief history of galaxies
Evolution of density inhomogeneities
z 0
Numerical calculations allow tracking of growth
through nonlinear regime.
Credit The VIRGO Cosmological N-body Project
http//www.mpa-garching.mpg.de/galform/virgo
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
9
A brief history of galaxies
Zoom through matter field at any instant Find
that structure is built hierarchically. Big
structures built from the repeated merger of
little structures.
Galaxies should merge a lot, especially at
moderate to high redshift!
http//www.mpa-garching.mpg.de/galform/virgo
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
10
Action shot High z mergers
Mergers in rich cluster MS 1054-03 (z 0.83)
Shown here 16 brightest galaxies. About 20 are
merging!
van Dokkum et al 1999, ApJ, 520, L95
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
11
Inaction shot Low z non-mergers
No mergers seen in MS 1358-62 (z 0.32)
Shown here 16 brightest galaxies. NO apparent
mergers!
van Dokkum et al 1999, ApJ, 520, L95
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
12
Black holes in galaxies
Orbits of stars in central few light days of the
center of the Milky Way.
Apply Keplers laws to these orbits, infer mass
M 3.5 x 106 Msun
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
13
Black holes in galaxies
Orbits of stars in central few light days of the
center of the Milky Way.
Apply Keplers laws to these orbits, infer mass
M 3.5 x 106 Msun
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
14
Black holes in galaxies
Water maser in core of Seyfert galaxy NGC4258
(M106), can accurately measure orbit of central
gas.
Apply Kepler
M 3.9 x 107 Msun
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
15
Black hole masses strongly correlated to
properties of galaxies
Trend Big bulge Big black hole
More precisely Deep central potential Big
black hole
s stellar velocity dispersion in galactic bulge.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
16
High z quasars
Black holes built up very rapidly We see quasars
at redshift z 6
Most extreme example so far SDSS 11485251 at z
6.4. Luminosity implies MBH (2-6) x 109 Msun!
Comparable to largest black holes at z 0 ...
but universe was Multiple merger episodes needed to grow from
seed scale this quickly (e.g., Li et al,
astro-ph/0608190)
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
17
The growth of black holes and galaxies is closely
related!
Mergers which drive the growth of galaxies must
also play a role in growing black holes
1. Way to feed gas to the black hole - drives
an episode of accretion, perhaps turns on
galactic activity.
2. Natural mechanism to build a massive binary
black hole. Coalescence of this binary grows a
black hole - second major contributor to black
hole growth.
The formation and evolution of galaxies naturally
produces LISA target signals!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
18
Consequence Structure growth drives
gravitational wave sources
Typical galaxy made from merger of many sub-units.
Big question How many subunits hosted black
holes?
Not clear what the initial distribution of
black holes is - wide range of possibilities
consistent with black hole distribution at z 0.
Example merger tree Final galaxy made from 20
subunit mergers. 4 binary black hole mergers en
route to final configuration. (Volonteri, Haardt,
Madau 2003).
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
19
Consequence Structure growth drives
gravitational wave sources
Typical galaxy made from merger of many sub-units.
Big question How many subunits hosted black
holes?
Examine range of models, always find an
interesting rate of binary formation. At least a
few events per year perhaps hundreds.
Example merger tree Final galaxy made from 20
subunit mergers. 4 binary black hole mergers en
route to final configuration. (Volonteri, Haardt,
Madau 2003).
(See, e.g., Haehnelt 1994 Menou, Haiman,
Narayanan 2001 Wyithe Loeb 2003 Islam,
Taylor, Silk 2004 Sesana et al 2004)
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
20
Rates highest at high z
Structure build up is most active at fairly high
redshift (z 2 or so) ... rate of binary black
hole mergers is likewise highest there.
Detail of rates depends on model assumptions,
particularly initial black hole population.
From Sesana, Haardt, Madau, and Volunteri, ApJ
2004.
An interesting LISA event rate appears guaranteed
by observations and modeling!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
21
Measuring these waves
Radiation is an oscillation in spacetime
geometry. In principle, measure it by bouncing
light between freely falling mirrors Bondi 1957
Lagrangian coordinates mirrors fixed at x 0,
L.
Light follows null geodesic in spacetime with
wave
Coordinate velocity of light
Gravitational wave h(t) h
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
22
LISA Direct implementation of Bondis idea!
Freely falling mirrors become freely falling
proof masses in drag free spacecraft. GWs read
out from changes in the rate of arrival of laser
phase fronts.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
23
LISA Direct implementation of Bondis idea!
Freely falling mirrors become freely falling
proof masses in drag free spacecraft. GWs read
out from changes in the rate of arrival of laser
phase fronts.
Spacecraft orbits passively maintain
constellation, keeping arms roughly fixed at 5 x
106 km.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
24
Measuring GWs from LISA signal
Three arms great for signal reconstruction Proper
ly combining the data from all 6 links (3 arms,
light travelling in both directions) allows us to
build both GW polarizations.
Begin with constellation in rest configuration,
all 3 arms at essentially the same length L.
Scott A. Hughes, MIT
NRC BE PAC, 6 November 2006
25
Measuring GWs from LISA signal
Three arms great for signal reconstruction Proper
ly combining the data from all 6 links (3 arms,
light travelling in both directions) allows us to
build both GW polarizations.
Plus polarization changes arms 1 and 2, leaves 3
unchanged
NOTE This calculation is strictly accurate only
for GW wavelength ? armlength L
Scott A. Hughes, MIT
NRC BE PAC, 6 November 2006
26
Measuring GWs from LISA signal
Three arms great for signal reconstruction Proper
ly combining the data from all 6 links (3 arms,
light travelling in both directions) allows us to
build both GW polarizations.
Cross polarization changes all three
NOTE This calculation is strictly accurate only
for GW wavelength ? armlength L
Scott A. Hughes, MIT
NRC BE PAC, 6 November 2006
27
Measuring GWs from LISA signal
Three arms great for signal reconstruction Proper
ly combining the data from all 6 links (3 arms,
light travelling in both directions) allows us to
build both GW polarizations.
Sanity check! If length changes are due to a GW,
they must satisfy
If sum is violated, we either have unanticipated
noise ... or a non-GR effect.
Scott A. Hughes, MIT
NRC BE PAC, 6 November 2006
28
Measuring GWs from LISA signal
Sensitive band runs from roughly 10-4 Hz to about
0.1 Hz
Notice odd shape near 10-3 Hz Noise due to
galactic binaries!
So many binary star systems in the galaxy that
they cannot be resolved, combine stochastically
to form a noise source.
Scott A. Hughes, MIT
NRC BE PAC, 6 November 2006
29
BBH waves in simulated LISA noise
Waves for m1 m2 2 x 105 Msun at z 5, plus
simulated LISA noise (including galactic binary
noise).
Signal is so loud at the end that it stands above
the noise with no sophisticated filtering!
Scott A. Hughes, MIT
NRC BE PAC, 6 November 2006
30
BBH signal strength HUGE!
Binary black hole signal visible over a wide
range of masses to large redshift!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
31
How well can we measure these waves?
Want to assess how well we can learn about the
system generating GWs.
Ingredients needed 1. Waveform model 2. LISA
response model 3. Formalism to estimate how
well properties of waves are determined by
measurement.
Past work focussing on LISA Cutler (PRD 1998)
Hughes (MNRAS 2002) Vecchio (PRD 2004) Berti,
Buonanno, Will (PRD 2005).
This talk Focus on Lang Hughes (PRD in press
gr-qc/0608062)
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
32
Measurement formalism
Maximum likelihood approach, originally developed
(in GW context) by Finn (PRD 1992).
Basic idea If noise spectrum is Gaussian, then
probability that a particular noise n(t) is
realized is
where
Suppose data contains waveform of a particular
binary black hole, htrue(t) s(t) htrue(t)
n(t).
What is the probability that a model hmodel(t)
describes that waveform?
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
33
Measurement formalism
If hmodel(t) accurately describes the true
waveform, then s(t) - hmodel(t) is pure noise!
Then, the likelihood that hmodel(t) is a good
description of the data is
Formula is basic tool to assess how well we can
do!
Recipe 1. Pick a binary with parameters ?i 2.
Examine how well binary with parameters ?i
d?i describes it 3. Use this to assess typical
level of error at a given likelihood level
(e.g., 1-s errors).
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
34
Wave model
Break coalescence into 3 epochs
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
35
Wave model
Break coalescence into 3 epochs
Inspiral Slow evolution driven by GW loss of
orbital energy and angular momentum.
Main focus of this talk! LISA measured inspirals
will last for months to years - very rich
structure, measured with high signal-to-noise,
makes it possible to study source characteristics
with great precision.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
36
Wave model
Break coalescence into 3 epochs
Merger Extremely violent dynamics of spacetime
Two black holes smash together, leaving one
behind.
Modeling requires rather large numerical
simulations. Recent breakthroughs have opened
this up - race is on to explore parameter space,
develop merger phenomenology.
Ultimate confrontation of classical gravity
theory with data!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
37
Last dance Merger of two BHs
Contours Curvature components corresponding to
polarization of GWs
Contours Curvature components corresponding to
x polarization of GWs
Movies courtesy GSFC Numerical Relativity Group
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
38
Wave model
Break coalescence into 3 epochs
Ringdown Last wiggles of the merger take the
form of a damped sinusoid.
Simply described using black hole perturbation
theory! Expect mix of modes each modes
frequency and damping time set by final mass and
spin.
Measure mixture of modes - measure final mass and
spin! Determine mass and spin with 0.01 - 10
accuracy (Berti, Cordoso, Will, PRD 2006).
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
39
Wave model
Break coalescence into 3 epochs
Inspiral Slow evolution driven by GW loss of
orbital energy and angular momentum.
2 masses
Well understood, 17 parameter waveform.
6 spin components
1 initial eccentricity
2 position angles
1 initial periapsis longitude
2 orientation angles
1 distance
1 initial semi-major axis
1 initial orbit anomaly
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
40
Wave model
Break coalescence into 3 epochs
Inspiral Slow evolution driven by GW loss of
orbital energy and angular momentum.
2 masses
Well understood, 15 parameter waveform after the
orbit circularizes.
6 spin components
1 initial eccentricity
2 position angles
1 initial periapsis longitude
2 orientation angles
1 distance
Orbits circularize quickly!
1 initial semi-major axis
1 initial orbit anomaly
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
41
Post-Newtonian waveform
Waveforms are written down in the restricted 2nd
post-Newtonian approximation
Phase computed using 2nd post-Newtonian equations
of motion.
Only lowest order (quadrupole) contribution to
amplitude included
Also include post-Newtonian equations of spin and
orbit precession!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
42
Angular momentum precession
Post-newtonian theory shows a magnetic-type
coupling of mass currents to spacetime.
Creates new forces, modifying orbit
acceleration also causes spins of binarys
members to precess.
Gravitomagnetic field due to other bodys spin
Gravitomagnetic field due to orbital motion
Form is dS/dt S x Bg
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
43
Angular momentum precession
Post-newtonian theory shows a magnetic-type
coupling of mass currents to spacetime.
Creates new forces, modifying orbit
acceleration also causes spins of binarys
members to precess.
Angular momentum is globally conserved J L
S1 S2 constant Means that the orbital plane
precesses to compensate. (Known as
Lense-Thirring precession in weak-field.)
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
44
Inspiral measurements
Most important piece Phase F(t). 103 - 105
radians accumulated over 1 year of measurement.
Strong function of masses and spins of binarys
black holes.
Inspiral through LISA band for binary at z 1 m1
3 x 106 Msun m2 106 Msun Spin 1 80
max Spin 2 50 max
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
45
Inspiral measurements
Most important piece Phase F(t). 103 - 105
radians accumulated over 1 year of measurement.
Strong function of masses and spins of binarys
black holes.
Zoom on waveform.
White curve Same waveform as previous. Red
curve Waveform for a binary that is identical,
except that m2 is 0.5 smaller.
No difference in first week.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
46
Inspiral measurements
Most important piece Phase F(t). 103 - 105
radians accumulated over 1 year of measurement.
Strong function of masses and spins of binarys
black holes.
Zoom on waveform.
White curve Same waveform as previous. Red
curve Waveform for a binary that is identical,
except that m2 is 0.5 smaller.
5 weeks Can see mismatch!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
47
Inspiral measurements
Most important piece Phase F(t). 103 - 105
radians accumulated over 1 year of measurement.
Strong function of masses and spins of binarys
black holes.
Zoom on waveform.
White curve Same waveform as previous. Red
curve Waveform for a binary that is identical,
except that m2 is 0.5 smaller.
10 weeks Strong mismatch
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
48
Inspiral measurements
Most important piece Phase F(t). 103 - 105
radians accumulated over 1 year of measurement.
Strong function of masses and spins of binarys
black holes.
Zoom on waveform.
White curve Same waveform as previous. Red
curve Waveform for a binary that is identical,
except that m2 is 0.5 smaller.
End Totally out of phase.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
49
Inspiral measurements
Most important piece Phase F(t). 103 - 105
radians accumulated over 1 year of measurement.
Strong function of masses and spins of binarys
black holes.
High sensitivity to phase provides high precision
on mass measurement.
Typically find individual redshifted masses
with (0.01 - 1) accuracy
Certain mass combinations (chirp mass) measured
factor 10 better.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
50
Inspiral measurements
To assess typical mass measurement accuracy,
survey parameter space with Monte Carlo.
Randomly populate sky with binaries randomly
distribute their orbit planes, orientations of
spin vectors. Randomly distribute merger time
over a 3-year mission lifetime.
104 binaries at z 1
m1 106 Mo m2 3 x 105 Mo
Peaks at 0.1 relative error! Distribution
confined to Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
51
Inspiral measurements
Dynamically varying piece of the amplitude
Function of angles that set the binarys position
on sky and orientation.
Angles vary due to detector motion and
relativistic precession. Variation encodes
binarys position, orientation, and orientation
of spin vectors.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
52
Inspiral measurements
Dynamically varying piece of the
amplitude Function of angles that set the
binarys position on sky and orientation.
Illustration of impact on waveform Same as
previous, but spins set to zero.
Very smooth evolution! (NB Ignoring detector
motion)
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
53
Inspiral measurements
Dynamically varying piece of the
amplitude Function of angles that set the
binarys position on sky and orientation.
Spins now cranked up! Spin 1 Spin 2 99
maximum
Strong frequency and amplitude modulation gives
spin precision Typically 0.1 - 10 accuracy on
both spins.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
54
Inspiral measurements
To assess typical spin measurement accuracy,
survey parameter space with Monte Carlo.
Randomly populate sky with binaries randomly
distribute their orbit planes, orientations of
spin vectors. Randomly distribute merger time
over a 3-year mission lifetime.
104 binaries at z 1
m1 106 Mo m2 3 x 105 Mo
Peaks at 0.1 - 1 absolute error! Distribution
confined to Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
55
Inspiral measurements
Slowly varying piece of amplitude Only grows due
to frequency evolution.
After fixing masses and angles, this piece
directly determines source luminosity distance!
A standard candle (or standard siren) ...
standardized by general relativity!!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
56
Inspiral measurements
Monte Carlo to explore parameter space and assess
how well distance to binary is measured.
Solid line Population is assumed to contain
rapidly rotating black holes. Precession solidly
breaks degeneracy between distance and
position/orientation angles.
104 binaries at z 1
m1 106 Mo m2 3 x 105 Mo
Peaks at 0.3 relative error! Distribution
confined to Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
57
Inspiral measurements
Monte Carlo to explore parameter space and assess
how well distance to binary is measured.
Dashed line Population is assumed to contain
slowly rotating black holes. Degeneracy between
distance and position/orientation angles not
broken as well.
104 binaries at z 1
m1 106 Mo m2 3 x 105 Mo
Peaks at 1 relative error! Distribution
confined to Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
58
Inspiral measurement summary
Low redshift (z 1)
Low mass (m1 m2 dm/m 0.01 is typical
dspin 0.1 is typical if m1/m2 1.
Medium mass (m1 m2 dm/m 0.1 is typical
dspin 0.1 - 0.2 is typical if m1/m2 1.
Higher masses
Accuracy degrades as waves move out of band.
(Note Ringdown is measured very accurately here.)
Precision black hole astrometry!!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
59
Inspiral measurement summary
High redshift (z 5)
Low mass (m1 m2 dm/m 0.1 - 1 is typical
dspin 1 is typical if m1/m2 1.
Medium mass (m1 m2 dm/m 1 - 40
dspin 1 - several x 100
High mass degradation cuts in at lower masses
Whole spectrum is shifted due to high redshift.
Expect lower masses to be more common at high
redshift - High mass end not so relevant here!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
60
Inspiral measurement summary
High redshift (z 5)
Low mass (m1 m2 dm/m 0.1 - 1 is typical
dspin 1 is typical if m1/m2 1.
Medium mass (m1 m2 dm/m 1 - 40
dspin 1 - several x 100
Even at high redshift, masses and spins are
typically determined with exquisite
accuracy LISA will be a tool for mapping the
cosmic evolution of black holes, tracing the
growth of structure in the universe!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
61
Inspiral measurement summary
Low redshift (z 1)
All masses dD/D 0.2 - 0.4 is typical
High redshift (z 5)
All masses dD/D 2 - 3 is typical
An absolutely calibrated distance measure of
incredible precision!
Can we take advantage of this amazing precision
to formulate cosmologically interesting
measurements?
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
62
A problem ...
Distance is directly measured ... redshift is not!
Why? Masses spins enter waveform as timescales
Timescales undergo cosmological redshift
inferred masses/spins likewise redshift. Dont
measure m ... measure (1 z) m.
Redshift is always degenerate with intrinsic
system parameters It cannot be determined from
GWs alone.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
63
Two tracks
1. Assume cosmography for the universe, use it to
invert distance/redshift relation.
Concordance cosmological model Friedmann-Roberts
on-Walker universe Spatially flat (Otot 1,
25 matter, 75 cosmological
constant) Hubble constant H0 75 km sec-1
Mpc-1.
Use this model, can easily write down z(D). Find
dz/z ? maxdD/D, d(cosmology)
Combine with mass and spin measurements Directly
map cosmological evolution of black hole masses
and spins!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
64
Two tracks
2. Identify electromagnetic counterpart to GW
event - read redshift directly from that!
If merger host can be identified (quasar or AGN
activity, galaxy morphology, ...), then distance
redshift can both be measured with high
accuracy.
Standard siren GW analog of standard candle.
Intrinsically precise ... and, absolutely
calibrated (by general relativity).
Holz Hughes, ApJ 2005, 629, 15
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
65
Locating the merger
Big challenge Identifying the host of the merger
in a relatively large field.
Hubble Deep Field!
Good localization 10 - 30 arcminutes by 3 - 10
arcminutes.
Will also have 3rd dimension (distance) Can
eliminate many galaxies from the field, cut down
on possible merger hosts.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
66
Locating the merger
Very difficult to locate the merger host in a
field that is a factor 10 - 20 times larger than
this, even with selection effects!
Hopefully something goes boom ... but cant
count on that.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
67
Conclusion
Gravitational waves from binary black holes are a
window into the dynamics of structure growth!
High event rate almost guaranteed Consequence of
how galaxies grow and the coevolution of galaxies
and black holes.
LISA offers precision data about this
process Will map the growth and spin evolution
of black holes over cosmic time. Perhaps even a
new ruler for measuring cosmic distances!
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006
68
Mergers make elliptical galaxies
Merger of disk galaxies produces a remnant galaxy
with spheroidal morphology
A massive elliptical galaxy when two large disks
collide, or a larger disk galaxy with a central
spheroidal bulge.
Scott A. Hughes, MIT
UFL Astrophysics Seminar, 1 Dec 2006