Gravitational waves observed from another cosmic collision of a pair of black holes

The new findings from the LIGO-Virgo team, that includes researchers from the Gravitational Wave group of the University of Birmingham’s School of Physics and Astronomy, follows only a few months after the first direct detection of gravitational waves, ripples in the fabric of space-time, and the first observation of a binary black hole merger reported on 11 February 2016.

The discovery, published in Physical Review Letters, is the latest by the Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA.

The gravitational waves of the Boxing Day signal were produced by a pair of black holes, of around 14 and 8 solar masses, that travelled for over a billion years before reaching Earth. LIGO observed the final second of this pair of black holes before they collided, at half of the speed of light, to form a new black hole.

In the collision the equivalent of a solar mass of energy was released into ripples of space-time, and a new black hole was formed, 21 times heavier than the Sun.

In its first four months of operation LIGO has unambiguously observed two binary black hole mergers. The next most significant candidate event during the whole observing run was recorded on 12 October 2015. Though consistent with a signal from a binary black hole, it is quieter than the two confirmed observations and therefore cannot be as confidently claimed as a detection.

Gravitational waves carry unique information about the some of the most violent phenomena of our Universe. However, they interact very weakly with particles and require incredibly sensitive instruments to detect.

The LIGO discoveries have already revealed a population of binary black holes, which was previously unknown, and have confirmed that the behavior of gravity in the strong and dynamic regime is consistent with Einstein’s theory.  Future observations are expected to provide important insights into neutron stars, the evolution of stars, supernovae and gamma-ray bursts.

As planned, the Advanced LIGO instruments are currently undergoing further commissioning activities and are expected to resume science observations later this year.

Over the coming years, the Advanced LIGO detectors will be ramped up to full power, increasing their sensitivity to gravitational waves and allowing more distant events to be measured. With the addition of further detectors, initially in Italy and later in other locations around the world, the team believe that early detections are only the ‘tip of the iceberg’ of gravitational astronomy.

Birmingham scientists continue to play a significant role in the search for gravitational waves and the interpretation of the results using current instruments, and in the design and development of future generations of gravitational wave detectors.

As members of the international team responsible for the detection of gravitational waves, they were awarded the Special Breakthrough Prize in Fundamental Physics and the Gruber Cosmology Prize in May of this year.