# Presentation: 594462

## Binary Black Holes 

**Binary Black Holes **
**and**
**Gravitational Waves**
***Part II: Focus on Binary Black Holes***
**Joan Centrella**** **
***NASA/GSFC***
**Beyond Einstein Teacher’s Academy**
** ****NASA Goddard Space Flight Center                      **
**July 24,  2007**

## Massive Black Holes...lurk at the centers of galaxies

**Most galaxies believed to have central MBH**

**Masses typically millions to billions times the mass of the Sun**
**First found in active galaxies**
**Jets emanating from centers of active galaxies**** **

##   Massive Black Hole binaries...                                	... are produced when galaxies merge

**	**

- 	0402+379      Separation ~ 24ly

-      NGC 6240                     Separation ~ 3000ly

*(X-ray: NASA/CXC/AIfA/D.Hudson & T.Reiprich et all;Radio:NRAO/VLA/NRL)** *

*(NASA/CXC/MPE/S.Komossa et al. ) *

-      Abell 400           Separation ~ 25,000ly

*(Rodriguez, et al. ApJ,       astro-ph/0604042)** *

## Intermediate mass & Stellar BH binaries...

**IMBHs: hundreds to thousands times the mass of the Sun**
**Stellar BHs: approx 10 times the mass of the Sun**

**IMBH & stellar BH binaries are strong GW sources for ground-based detectors such as LIGO...**

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

evidence for stellar BHs in LMXBs

## Black hole binaries 

**Black hole binaries **
**     ****are *****strong *****sources of ****	****  ****	****   gravitational waves...**

## Gravitational waveforms are a map of the binary motion...

## GWs from final merger of a black hole binary...

**Strong-field merger is brightest GW source**
**Luminosity***** ***** ~ 10****23*****L*****SUN****    ******** outputs more energy than all the stars in observable universe combined!**

*(graphic courtesy of Kip Thorne)*

***can only be calculated on a computer!***

***use merger waveform to test GR in strong-field regime!***

## A numerical relativity primer....

**Solve Einstein’s equations numerically**
**Slice 4-D spacetime into a stack of 3-D slices**
**Start the binary in its initial state on a slice at some time**
**Evolve forward in time, from one slice to the next**
**Typically solve ****17 or more nonlinear, coupled partial differential equations**

## Some subtleties....crucial for success

**How do you slice the spacetime when you are near a black hole?**
**How do you set up a grid of coordinates on each slice?**
**And...how do prevent that grid from being swallowed up by the strong gravity of the black holes?**
**A black hole has a singularity – a point of infinite curvature – at its center.  How do you represent that on a computer?**
**The gravitational waves emitted have wavelengths much larger than the size of the binary orbit.  How do you get enough detail in your grid near the black holes, and near the waves?**
**To make things simple, we’ll use some special units:**
**Setting c = G = 1 allows us to measure distances and times in “mass” units **
**     ******** ****1 M ~ 5 x 10****-6**** (M/M****Sun****) sec ~ 1.5 (M/M****Sun****) km**

## A Brief History of BBH simulations....

**1964: Hahn & Lindquist: try to evolve collision of 2 “wormholes” **
**1970s: Smarr and Eppley: head-on collision of 2 BHs, extract GWs**
**Pioneering efforts on supercomputers at Livermore Natl Lab**
**1990s: LIGO moves ahead & work on BBH problem starts up again..**
**Work on 2-D head-on collisions at NCSA**
**NSF Grand Challenge: multi-institution, multi-year effort in 3-D**
***	************ ******This is ***_***really***_*** difficult!  Instabilities, issues in formalisms, etc...***
**Multiple efforts (AEI, UT-Austin, PSU, Cornell...)**
**Difficulties proliferate, instabilities arise, codes crash.... **
***“******Numerical relativity is impossible...”***
**2000s: LIGO/GEO/VIRGO and LISA spur more development**
**New groups arise: Caltech, UT-Brownsville, LSU, NASA/GSFC...**
**Since 2004.....*****                                                                     ***
**Breakthroughs & rapid progress throughout community**
**Orbits, waveforms, and astrophysical applications....**

## The 1st complete binary black hole orbit...

**Bruegmann, Tichy, & Jansen, PRL, 92, 211101 (2004), gr-qc/0312112*******
**equal mass, nonspinning BHs**
**Represent BHs as “punctures” that are fixed in the computational grid**
**Use “comoving” coordinates**
****For gr-qc and                                   astro-ph papers,                              see *****http://arxiv.org/**

**“****traditional” techniques**
**Runs for ~ (125 – 150)*****M*****  and BHs complete ~ 1 orbit**
**Crashes before BHs merge**
**Not accurate enough to be able to extract GWs  **

## The 1st orbit, merger, & ringdown...

**Pretorius, PRL, 95, 121101 (2005) gr-qc/0507014**
**Very different techniques**

**Excised**** BHs move through grid**
**Equal mass, nonspinning BHs**

## A new idea: “moving puncture BHs”

**Allow puncture  BHs to move across grid w/out excision**
***Simultaneous, independent***** discovery by UTB & GSFC groups:**
**Campanelli, et al., PRL, 96, 111101 (2006), ****gr-qc/0511048**
**Baker, et al., PRL, 96, 111102 (2006), gr-qc/0511103**
**Uses traditional numerical relativity techniques **
**Enables long duration, accurate simulations**

## A powerful new idea....that spread rapidly

**Developed w/in  “traditional” numerical relativity approach**
**Represent BHs as punctures and *****allow them to move***
**Requires novel – yet simple – slicing and coordinates**
**UTB, GSFC moved ahead rapidly, quickly do multiple orbits**
**Moving punctures quickly adopted by many other groups:**
**PSU, AEI/LSU, FAU/Jena...**
**At April 2006 APS meeting, a                                                           full session devoted to BBH                                                   mergers w/ moving punctures!**
**Summer 2006: method adopted                                                       by most of community**
**2007: many new results                                                         coming out quickly! **

**Campanelli, et al., PRD, 73, 061501 (2006), gr-qc/06010901**

## Revealing universal behavior...

**Baker, al., PRD, 73, 104002 (2006), gr-qc/0602026   **
**Equal mass, nonspinning BHs**
**Run several cases, starting from successively wider separations**
**BH orbits lock on to universal trajectory ~ one orbit before merger**
-    BH trajectories (only 1 BH shown)                                                                                                                                						BH separation vs. time

## Universal waveform....

***Universal waveform....***

- Universal dynamics produces universal waveform....
- All runs agree to within < 1% for final orbit, merger & ringdown

## Comparison of gravitational waveforms...

**Baker, Campanelli, Pretorius, Zlochower, gr-qc/0701016**
- Compare GWs from equal mass, nonspinning case
- 3 different , independently-written codes

## Binary Black Holes: The Movies           

**+****  polarization**

- x** ** **polarization**

***(Visualizations by Chris Henze, NASA/Ames)***

## Longer runs, start in late inspiral... 

**Baker, et al., gr-qc/0612117**
**Lower initial eccentricity e ~ 0.008**
**Evolve ~ 1200M and ~ 7 orbits before merging**
**Agreement to < 1% for merger/ringdown  burst, t > -50M**
**Differences for inspiral portion of waveforms...**

## Comparison with earlier results... 

**Less eccentricity in orbits...more realistic model for a real BH-BH binary!**
-                   **BH separation vs. time**

## “Observing” the mergers...

**Baker, et al., gr-qc/0612117**
**Make composite waveform**
**Use this as a “signal” for LIGO and LISA**
**Examine how well these detectors can “observe” these sources...**

## Detecting BH mergers with LIGO...

**Contours of signal-to-noise...**

**Advanced**
**LIGO**

## Observing MBH mergers with LISA....

**      ****Note: for M>10****7**** M****sun****, may not merge in < T****Hubble**** **

## Sample BBH waveform seen as by LISA....

**Total mass M=10****5****M****SUN**** MBH binary at z = 15 **
**Put signal into LISA simulator with instrumental noise and WD-WD stochastic background**

## Equal mass BHs with spin...

**Campanelli, et al.,  Phys.Rev. D74 (2006) 041501** (**gr-qc/0604012)**
**1****st**** BH mergers with spin**
**Equal masses, each with a = 0.75 m**
**Anti/aligned ******** attractive/repulsive**
**Final a=0.9M (aligned), a=0.44M (anti)**

## Recoil kicks from BBH mergers...

**When the masses are not equal:**
**the GW emission is asymmetric **
**the GWs are “beamed” in some direction...**
**Since the GWs carry momentum, the final BH that    forms suffers a recoil ‘kick’ in the opposite direction!**
**If this kick velocity is large enough, the final BH that forms could be ejected from its host structure!**
**Need numerical relativity simulations for accurate results...**

## Recoil kicks from BBH mergers...

**Nonspinning BHs with m****2 ****≠ m****1****  **
**Baker et al. ****ApJL, 653, (2006) L93                (astro-ph/0603204)**
**m****1**** = .67 m****2**** ******** V****kick**** ~ 90 km/s**
**Gonzalez, et al. ****PRL. 98 (2007) 091101              (gr-qc/0610154)**
**found maximum ****V****kick**** ~ 176 km/s                        for m****1**** ~ .36 m****2**** **
***Interesting, but not terribly “dangerous” –                        ******	******	******	******	******	******	******However.....                      ***

## Recoil kicks from BH mergers w/spin...

**Anti/aligned spins: spins are perpendicular to the orbit of the BHs**
**For equal masses:**** **
**Herrmann, et al., gr-qc/0701143 **
** ****v****kick**** up to ~ 400 km/s**
**Koppitz, et al., gr-qc/0701163 **
** ****v****kick**** up to ~ 250 km/s**
**For unequal masses, the kick velocities are generally smaller**
**                                                             *****But...***

## If the BH spins are not perpendicular to the orbital plan...

**Such mergers can produce much larger kick velocities**
**Gonzalez et al*****. *****(gr-qc/0702052), Tichy & Marronetti           (gr-qc/0703075): show v****kick ****~2000 km/s!**
**Campanelli et al*****.                                                                       *****(gr-qc/0701164):                                                                                                        predict possible                                                                        max kicks up to                                                                         v****kick ****~ 4000 km/s!**

## Spinning Black Holes: The Movies           

**m****1**** = m****2**
**each BH has           a/m ~ 0.9**
**Final BH has:**
**a/m ~ 0.67**
**v****kick**** ~ 1500 km/s        in +z direction**

***(Visualizations by Chris Henze, NASA/Ames)***

## Current status of BBH merger simulations...

- Impressive recent progress on a broad front: many research groups, different codes, methods...
- Equal mass, nonspinning BBHs: several groups are now evolving for several orbits, followed by the plunge, merger, and ringdown
- There is general agreement on the ***simple waveform shape*** and that
- total GW energy emitted in last few cycles
- 		ΔE ~ (3.5% - 4%)M   *(depends on the number of  orbits)*
- final BH has spin a ~ 0.7M
- Long runs now possible...~ 7 orbits before merger
- Applications to GW data analysis are beginning
***Explosion*** of work on nonequal mass and spinning BH mergers and the resulting kicks
- Very interesting results coming out
- Important astrophysical applications...

## The emerging picture....

***The emerging picture....***

## Stay Tuned!

***Stay Tuned!***