# Presentation: 243365

## Gravitational Wave Astrophysics, Compact Binaries,                         and Numerical Relativity

**Joan Centrella**
**Gravitational Astrophysics Laboratory**
**NASA/GSFC**

***Numerical Relativity 2005: Compact Binaries******                   ******November 2 – 4 , 2005***

## Most of the information we have about the Universe so far has come to us in the form of . . . 

- Electromagnetic radiation
- Visible light: naked eye observations,optical telescopes
- Full electromagnetic spectrum:  radio, IR, UV, visible, X-rays, Gamma-rays
- Particle & nuclear astrophysics, neutrinos, cosmic rays...

***These cosmic messengers provide a wealth of information, making astronomy one of the crowning glories of 20******th****** century science.***

## A Different Type of Astronomical MessengerGravitational Waves . . . 

**ripples in spacetime curvature**
**travel at velocity *****v***** = *****c***
**generated by matter distributions w/ time-changing quadrupole moments    **
****** *****carry info about bulk motion                                                                                                                                                                                                                                                                                       of sources***
**transverse ******** act normal to propagation direction**
**2 polarization states, h****+**** and h****x**
**interact weakly with matter **
****** *****carry info about deep, hidden regions in the universe***

**Hulse-Taylor binary pulsar       PSR 1913+16**
**Orbital period decay agrees with GR to within the     obs errors of < 1%**
**Nobel Prize 1993 **

**Notes:**
Here, put in polariz picture from LISA doc...

## Characteristic amplitude 

r = distance to source
RSch = 2GM/c2
Q = (trace-free) quadrupole moment of source
v = characteristic nonspherical velocity            in source

***r***** = distance to source**
**R****Sch**** = 2GM/c****2**
***Q***** = (trace-free) quadrupole moment of source**
***v***** = characteristic nonspherical velocity            in source**

***Amplitudes of Gravitational Wave Sources . . .***

**Estimate upper limits:**
**1.4 M****Sun**** NS at**
***r***** = 15 kpc, *****h***** ~ 10****-17**
***r***** = 15 Mpc, *****h***** ~ 10****-20**
***r***** = 200 Mpc, *****h***** ~ 10****-21**
***r***** = 3000 Mpc, *****h***** ~ 10****-22**
**4 x 10****6**** M****sun**** MBH at**
***r***** = 3000 Mpc, *****h***** ~ 10****-16**

***  ******Strongest sources have***
***      ******large masses moving***
***      ******with velocities v ~ c ***

**Notes:**
Q = trace-tree quadrupole moment

R = 200 Mpc is best guess for several NS/NS per year

Pat – perhaps LH panel should appear first, then add RH panel?

## Detecting gravitational waves. . .

- Resonant mass detectors, laser interferometers
- Detector of length scale *L*
- A passing gravitational wave causes distortion of detector that produces a ***strain amplitude*** ***h(t) = ******Δ******L/L***
- Source waveforms scale as ***h(t) ~ 1/r***

*(graphic courtesy of B. Barish, LIGO-Caltech)*

**Notes:**
Laser interferometers are current and future detectors...

Put in Barish graphic
Fix delta – use Greek symbol

Note as L increases, need to measure a smaller delta L for a given strain h

## Estimating Gravitational Wave frequencies . . .

**Natural frequency **
**1.4 M****Sun**** NS, *****R***** = 10 km**
***f******o***** ~ 2 kHz**
**10 M****Sun**** BH**
***f******o***** ~ 1 kHz**
**4 x 10****6**** M****Sun**** MBH**
***f******o***** ~ 3 mHz**

**Binary orbital frequency**
** **
***M***** = *****M*****1**** + *****M*****2****, *****M*****1**** = *****M*****2**
***a***** = separation**
**NS/NS, *****a***** = 10 *****R***
***     ******f*****GW**** ~ 200 Hz**
**BH/BH, *****a***** = 10 *****M***
***     ******f*****GW**** ~ 100 Hz**
**MBH/MBH, *****a***** = 10 *****M***
***f*****GW**** ~ 3 x 10****-4**** Hz**

**Notes:**
M = mass of source, R = radius of source for NS,
R = 2GM/c^2 for BH  -- use R_Sch

For BH/BH, MBH/MBH, a = 10M = 10 R

## Ground-based interferometers . . . 

- detect high frequency GW
- broad band
- kilometer-scale arms
- Current projects:
- LIGO: Hanford, WA, and     Livingston, LA;  *L* = 4 km
- VIRGO: France/Italy,                      near Pisa;  *L* = 3 km
- GEO600: Germany/Britain,     Hanover; *L* = 600 m
- Typical sources: NS/NS, NS/BH, BH/BH,  stellar collapse, LMXBs...

**Notes:**
Include graphic – photo of LIGO detector

note low freq limit determined by seismic noise on earth

## Significant progress in ground-based GW detectors....

LIGO:
has a set of running detectors
data analysis process has matured
the main initial LIGO science run S5
to take 1 full year of integrated data
set to begin later this year
reorganization of LIGO lab and LSC into a single “LIGO”
Advanced LIGO upgrade 
showing good technical progress
optimistic about starting funding from NSF in 2008
VIRGO, GEO600: 
also progressing

 the age of GW observations is beginning in earnest!

- LIGO:
- has a set of running detectors
- data analysis process has matured
- the main initial LIGO science run S5
**to take 1 full year of integrated data**
**set to begin later this year**
- reorganization of LIGO lab and LSC into a single *“LIGO”*
- Advanced LIGO upgrade
**showing good technical progress**
**optimistic about starting funding from NSF in 2008**
- VIRGO, GEO600:
- also progressing
-  ***the age of GW observations is beginning in earnest!***

## LISA: Laser Interferometric Space Antenna

- NASA/ESA collaboration
- detect low frequency GW
- 3 spacecraft
- equilateral triangle
- orbits Sun at 1 AU
- 20o behind Earth in its orbit
- arm length *L* = 5 x 106 km
- optical transponders receive and re-transmit phase locked light
- launch ~ 2015
- Typical sources: MBH/MBH, Galactic compact binaries, NS/MBH, BH/MBH

**Notes:**
Need to go into space to detect GW with f < 1 Hz...

## Recent LISA Accomplishments...

- The LISA Project has been in the Formulation Phase one year.
- ESA has engaged a contractor for formulation studies.  The Architecture Definition Phase of that contract is complete.
- The LISA Project team has mapped out 35 design studies, 13 are done, 5 are ongoing, and the rest to be finished by Apr. ‘06.
- LISA Pathfinder’s major milestone, the Preliminary Design Review, is nearly complete.  ESA’s LISA Test Package has built and tested engineering models.  NASA’s ST-7 has built and tested engineering models.
- Ground-based technology development is progressing on microthrusters, phasemeter, lasers, etc.
- LISA data analysis planning has started both in the U.S. and Europe.

## Gravitational Reference Sensor

- Engineering model of the gravitational reference sensor for LISA Pathfinder

## Interferometry

- Engineering model of the interferometer for LISA Pathfinder

## LISA / LIGO Relationship

***LISA / LIGO Relationship***

- Complementary observations, different frequency bands
- Different astrophysical sources

## Astrophysical black holes....

- Black holes are formed throughout the universe as the extreme end states of collapse, accretion, mergers....
- There is good evidence for BHs in 3 mass ranges:
- massive black holes (MBHs): *M* ≥ 105 Msun
- intermediate mass black holes (IMBHs): 102 Msun ≤ *M* ≤ 104 Msun
- stellar black holes: *M*  ≤ 102 Msun
- BHs are powerful cosmic engines, heating and accelerating gas and particles to produce impressive displays of electromagnetic energy...
- When occuring in a binary, BHs are also prodigious sources of gravitational waves....

## Massive Black Holes...first found in active galaxies..

**M87: giant elliptical galaxy with jet**
**Cyg-A: radio source: jet                 extends ~ 7 x 10****5**** ly**

**optical (AURA/NRAO/NSF)**

**VLA(top left), HST (top right), VLBI (bottom) (NASA,NRAO/NSF,STScI/JHU, AUI)**

**(NRAO/AUI)**

## Massive Black Holes....

- Good evidence for “massive dark objects” with masses                          106 Msun < *M* < 1010 Msun at  centers of ~ few dozen galaxies
- Based on dynamical models, the case for these massive dark objects  being ***MBHs*** is tight for ~ 3 galaxies...
- MBH masses correlate with bulge luminosity (left) and velocity dispersion (right)                                                                            (Ferrarase & Ford 2005)
- MBH ~ σ4 – 5

-  LISA observations of GW from compact objects inspiralling into these objects can falsify the hypothesis that they are actually Kerr BHs

## MBH/MBH  binaries....

***MBH/MBH  binaries....***

**MBHs at the centers of most, if not all, galaxies**
**Most galaxies undergo at least one merger**
**	******** *****MBH binaries***
**Coalescence of MBH binary depends on stellar effects, gas, feedback....**
**Chandra X-ray observatory found the first known system of 2 MBH starting to merge in the galaxy NGC 6240**
**distance ~ 120 Mpc ******** close!**
**BHs will merge in ~ few x 10****8**** yrs**
**LISA could observe ~ several tens per year, out to redshifts  z > 5 or more**

## Evidence for MBH mergers....

**Jets emanating from  centers of active galaxies**** **
**believed to result from accretion onto central MBH**
**jet directed along spin axis**
**Mergers of spinning BHs can change orientation of BH spin axis**
**	**** ******** ****sudden flip in jet direction**
**X-type radio  sources may be                                                              signature of MBH merger       **

*(Merritt & Ekers, Science, 2002)*

**(Image courtesy of NRAO/AUI & Inset: STScI)**** **

## IMBHs....X-ray sources in dense stellar clusters

**M82: active star-forming galaxy ******
**many young, dense stellar clusters & luminous X-ray sources (ULXs)**
**associate  cluster MGG – 1 w/ ULX  M82 X-1 (near center of image)**
**Identify this w/ IMBH of mass      M ****≥**** 350 M****sun**** ****(Portegies Zwart, et al)**

**M74: Optical image w/ Chandra X-ray image overlaid**
**Sc spiral galaxy with ULX**
**ULX is IMBH candidate**

**(Optical: NOAO/AURA/NSF/T.Boroson**
**X-ray: NASA/CXC/U. of Michigan/J.Liu et al.)**

## IMBH/IMBH  binaries....

**IMBHs can form in dense stellar clusters (Miller, Freitag,...)**
**stellar dynamics**
**collisions**
**core collapse of cluster**
**runaway ******** form IMBH**
**Can > 1 IMBH form in a stellar cluster?**
**recent simulations by John Fregeau and collaborators find multiple sites for runaway to occur in clusters**
****** ****multiple IMBHs form, with comparable masses m****1****/m****2**** < 10**
**LISA could see as many as several inspirals per year, for masses in the range *****M***** ~ few x 100 M****sun**** – 10****3**** M****sun**
**Advanced LIGO could see binaries with masses in the range *****M***** ~ (10s – 100s)M****sun**** **

## Stellar Black Holes....

**Form as the end result of massive star evolution**
**Type II supernova: **
**collapse of iron core in highly evolved massive star**
**outer regions blasted away in supernova explosion**
**core collapses to BH if mass of remnant core M > 3 M****sun**** (maximum mass of NS)**
**Evidence for BH strongest in low mass X-ray binaries (LMXBs)**
**interacting binary systems with compact object and companion star**
**accretion of material from companion onto compact object ******** X-rays **
**in ~ 17 cases, compact object has                                                           mass M > 3 M****sun**** ******** BH (Orosz)**
**BH/BH binary:**
**forms if companion evolves to BH w/out                                      disrupting binary**
**no gas ******** no EM emission**
**but...detectable by GWs**
**Source for ground based detectors....**

*(Ihle 2004)*

## Final coalescence of BH binary proceeds in 3 stages . . .

- GW produced in all three phases of this evolution . . .
- Waveforms and dynamics scale with BH masses and spins
-  	 source modeling applicable to
- 	    stellar BHs, IMBHs & MBHs....

*(graphic courtesy of Kip Thorne)*

***measure masses and spins of binary BHs***

***detect normal modes of ringdown to identify final Kerr BH***

* ****strong-field spacetime dynamics, spin flips and couplings...***

## Focus on the merger stage...

- Inspiral lasts until last stable orbit (LSO) ...then BHs           leave quasi-static orbits and plunge together
- Need to evolve BH binary for ~ few orbits near the              LSO at the end of the inspiral, through merger and ringdown...and extract the GW signature
- Expect ~ several cycles of gravitational radiation from merger
**“****burst” waveform, observable  by LISA for ~ minutes – hours**
- Strong, highly nonlinear, dynamical gravitational fields
- Importance of astrophysical initial data...
- Requires numerical solution of full Einstein eqs in 3-D + time...
- Merger can be phenomenologically rich
**effects of spin: spin-spin and spin-orbit couplings, spin flips**
**test of GR in the dynamical, nonlinear regime**
**possible ejection of final BH for *****M*****1**** ****≠ *****M*****2****  *********** ******astrophysics***

## What powers short Gamma-ray bursts?

- Gamma-Ray Bursts (GRBs) come in 2 types: long (> 2 sec) and short
- The burst is followed by a fainter, longer lived “afterglow”
- By observing their afterglows, long GRBs are associated with the collapse of young, massive stellar cores
- Recent observations by HETE & Swift allowed fast and precise localization of X-ray afterglows of some short GRBs
- Left: GRB 050509b observed by Swift’s γ-ray (blue) & X-ray (red) instruments
- Right: GRB 050724 observed by Swift’s X-ray telescope (red) and the small circles and crosses are from optical, X-ray (Chandra) and radio observations

## Short GRBS....NS/NS and NS/BH mergers?

- These observations of short GRBs are consistent with models of NS/NS or NS/BH mergers
- Such events would also produce GWs that could be detectable by ground-based detectors such as LIGO
- Can tell us about the populations     of such compact binaries, and the GRB mechanisms
- Will look for coincidences  between Swift and HETE events and possible GW signals during  the upcoming S5 science run

***(Nature)***

## “Every time you build new tools to see the universe, new universes are discovered.  Through the ages, we see the power of penetrating into space.”

*-- David H. DeVorkin (paraphrasing Sir William Herschel)*

- Gravitational Waves . . .
- 	*a new kind of cosmic messenger*

## Slide 29