GW151226

GW151226
Name	GW151226
Event date	2015-12-26
Detectors	LIGO Hanford, LIGO Livingston
Significance	>5σ
Masses	14.2+8.3–3.7 M☉ and 7.5+2.3–2.3 M☉
Final mass	20.8+6.1–1.7 M☉
Luminosity distance	440+180–190 Mpc
Redshift	0.09+0.03–0.04
Spin	positive aligned component for more massive black hole

GW151226 was the second confirmed gravitational-wave detection announced by the Laser Interferometer Gravitational-Wave Observatory collaborations in 2016. The signal originated from a compact binary coalescence observed on 26 December 2015 and provided independent evidence for stellar-mass black hole binaries and for black hole spin. The observation complemented the earlier event announced in 2016 and contributed to a growing catalog used by multiple observatories and theoretical groups.

Background

The detection followed upgrades at the LIGO Scientific Collaboration facilities at Hanford and Livingston, which were part of the Advanced LIGO project, a partnership that involved institutions such as the Massachusetts Institute of Technology, the California Institute of Technology, and national laboratories including Caltech and the U.S. National Science Foundation. The observation occurred in the era of multi-messenger initiatives involving collaborations like the Virgo Collaboration, the European Southern Observatory, and the National Aeronautics and Space Administration through programs that coordinate follow-up among observatories such as the Fermi Gamma-ray Space Telescope, Swift, and ground-based arrays including the Pan-STARRS survey and instruments at the Cerro Tololo Inter-American Observatory. Theoretical foundations draw on work by researchers associated with institutions like Princeton University, Stanford University, Cambridge University, and the Max Planck Institute for Gravitational Physics.

Detection

The signal was recorded by the LIGO Hanford Observatory and LIGO Livingston Observatory interferometers during the second month of the first observing run of Advanced LIGO, with data analysis pipelines developed by teams at the LIGO Scientific Collaboration, Virgo Collaboration, and affiliated groups at the Australian National University, Cardiff University, and University of Glasgow. Detection algorithms incorporated matched-filter banks constructed by researchers from University of Birmingham, Massachusetts Institute of Technology, Caltech, and Cornell University. Alerts triggered outreach and coordination with facilities such as Keck Observatory, Very Large Telescope, Subaru Telescope, and radio arrays including the Karl G. Jansky Very Large Array and the Australian Square Kilometre Array Pathfinder. Confirmation and parameter estimation involved computing resources at centers like the San Diego Supercomputer Center and the European Grid Infrastructure.

Source properties

Parameter estimation teams from LIGO Laboratory, Virgo Collaboration, and contributing institutions such as University of Wisconsin–Milwaukee, Cardiff University, University of Florida, and Monash University inferred component masses and spins using waveform models developed at Caltech, MIT, Max Planck Institute for Gravitational Physics, and University of Cambridge. The system consisted of two stellar-mass compact objects consistent with black holes, with component masses estimated around fourteen and seven solar masses, producing a final black hole mass near twenty-one solar masses. Distance and redshift estimates placed the source at cosmological distances relevant to surveys by Sloan Digital Sky Survey, Two Micron All Sky Survey, and Pan-STARRS. The analysis reported evidence for nonzero aligned spin consistent with formation scenarios discussed in studies from Yale University, University of Chicago, University of Texas at Austin, and Caltech.

Significance and implications

The detection influenced astrophysical population studies by teams at Max Planck Institute for Astrophysics, Institute of Astronomy, Cambridge, Harvard University, Princeton University, and Rutgers University, informing models of binary stellar evolution developed at University of Birmingham, University of Cambridge, Monash University, and Cardiff University. It contributed to constraints on black hole natal kicks and metallicity-dependent formation channels investigated by groups at Northwestern University, University of California, Berkeley, Columbia University, and Flatiron Institute. Cosmological implications intersected with methods advanced by researchers at Perimeter Institute, University of Oxford, Imperial College London, and Yale University for using gravitational-wave sources as standard sirens in conjunction with electromagnetic surveys like Dark Energy Survey and missions such as Euclid and WFIRST.

Data analysis and waveform modeling

Waveform modeling combined numerical relativity results from teams at the Albert Einstein Institute, Caltech, Cornell University, and Georgia Tech with analytical post-Newtonian formalisms developed at Institut de Physique Théorique, University of Maryland, and University of Southampton. Parameter estimation utilized Bayesian inference frameworks and sampling algorithms implemented by groups at University of Cambridge, University of Birmingham, Sapienza University of Rome, and University of Pisa. Model comparisons tested frameworks such as effective-one-body models from Università di Milano–Bicocca teams and phenomenological waveforms from the Max Planck Institute for Gravitational Physics, constrained by computational resources at facilities like National Energy Research Scientific Computing Center and Compute Canada.

Follow-up observations and electromagnetic searches

After the public announcement, coordinated follow-ups involved observatories and collaborations including Fermi Gamma-ray Space Telescope, INTEGRAL, Swift, Chandra X-ray Observatory, XMM-Newton, optical teams at Pan-STARRS, Zwicky Transient Facility, and Dark Energy Camera, and radio follow-up by Very Large Array and LOFAR. No confirmed electromagnetic counterpart was associated with the event, consistent with expectations for binary black hole mergers discussed in studies from University of Arizona, Carnegie Institution for Science, California Institute of Technology, and University of Florida. Upper limits from these searches informed joint analysis efforts led by groups at LIGO Scientific Collaboration, Virgo Collaboration, NASA, and partner universities such as Stanford University and University of Hawaiʻi.

Category:Gravitational-wave sources