23 June 2020
Visualisation of the coalescence of two black holes that inspiral and merge, emitting gravitational waves. One black hole is 9.2x more massive than the other and both objects are non-spinning. The high mass-ratio amplifies gravitational-wave overtones in the emitted signal. The gravitational-wave signal produced is consistent with the observation made by the LIGO and Virgo gravitational-wave detectors on August 14th, 2019 (GW190814).
Credit : N. Fischer, S. Ossokine, H. Pfeiffer, A. Buonanno (Max Planck Institute for Gravitational Physics), Simulating eXtreme Spacetimes (SXS) Collaboration.
Scientists working on an international experiment, part-funded by the Science and Technology Facilities Council (STFC), have discovered a massive object in space that may change our understanding of the largest stars in the Universe.
When the biggest stars die, they collapse under their own gravity and leave behind black holes; when stars with less mass die, they explode in a supernova and leave behind dense, dead remnants, called neutron stars.
On August 14 last year, the US-based National Science Foundation's Laser Interferometer Gravitational-Wave Observatory (LIGO), part -funded by the STFC, and the European Virgo detector picked up a gravitational wave signal from the merger of two astronomical objects. Gravitational waves are ripples in space caused by massive cosmic events such as the collision of black holes or the explosion of supernovae.
New research published today explains the detection of a mystery signal, dubbed GW190814, using gravitational wave detectors, in what's known as the 'Mass Gap'. This is the gap between the largest known neutron star and the lightest ever detected black hole.
The newly discovered object is 2.6 solar masses and is therefore either the heaviest neutron star or the lightest black hole ever detected. This puts it firmly in the mass gap between neutron stars and black holes. The object merged with a black hole of 23 solar masses. At a ratio of 9:1, it is also the largest difference in masses yet observed, during a collision, by gravitational wave astronomers.
This graphic shows the masses for black holes detected through electromagnetic observations (purple), the black holes measured by gravitational-wave observations (blue), the neutron stars measured with electromagnetic observations (yellow), and the neutron stars detected through gravitational waves (orange). GW190814 is highlighted in the middle of the graphic as the merger of a black hole and a mystery object around 2.6 times the mass of the sun.
Credit: LIGO-Virgo/ Frank Elavsky & Aaron Geller (Northwestern)
Professor Alberto Vecchio, director of the Institute for Gravitational Wave Astronomy at the University of Birmingham said:
“We have been itching with excitement since this candidate showed up on our screens. We thought the Universe would be kind of lazy in producing binaries of objects with such different masses, if it did so at all. And guess what, we were wrong!
We now know there are cosmic factories hiding somewhere that are rather efficient at generating these systems. The journey to figure out what they are and how they work is going to keep us busy for quite some time, but more and better data from LIGO and Virgo are just about a year away, and we are bound to have new surprises”.
The new observation is important because it challenges astrophysicists' understanding both of how stars die and how they pair up into binary systems. A binary system is a system of two astronomical bodies that are close enough for their gravitational attraction to make them orbit each other around a central point. This is the centre of the mass of the two bodies.
The discovery challenges current theoretical models. More cosmic observations and research will need to be undertaken, to establish whether this new object is indeed something that has never been observed before or whether it may instead be the lightest black hole ever detected.
The detections were only made possible by combining UK technology, sustained international funding, and enormous dedication and hard work by more than a thousand scientists from around the world. The LIGO Scientific Collaboration comprises over 1000 scientists from 17 countries, and includes researchers from ten UK universities (Glasgow, Birmingham, Cardiff, Strathclyde, West of Scotland, Sheffield, Edinburgh, Cambridge, King College London and Southampton).
LIGO is funded by the US-based National Science Foundation (NSF) and operated by Caltech and MIT, which conceived of LIGO and lead the project. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council- STFC) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. Approximately 1,300 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration.
A list of additional partners is available at https://my.ligo.org/census.php.
The Virgo Collaboration is currently composed of approximately 520 members from 99 institutes in 11 different countries including Belgium, France, Germany, Hungary, Italy, the Netherlands, Poland, and Spain. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy, and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and Nikhef in the Netherlands. A list of the Virgo Collaboration groups can be found at http://public.virgo-gw.eu/the-virgo-collaboration/. More information is available on the Virgo website at http://www.virgo-gw.eu.
LIGO consists of two L-shaped interferometers, one in Hanford, Washington, and one in Livingston, Louisiana. Each arm of each L is 2½ miles (4 km) long. Lasers look for changes in each arm's length as small as a millionth the diameter of a proton. Passing gravitational waves might distort space-time by that much.
The first detection of gravitational waves, announced on February 11, 2016, was a milestone in physics and astronomy; it confirmed a major prediction of Albert Einstein’s 1915 theory of general relativity, and marked the beginning of the new field of gravitational-wave astronomy.
Then, on October 16, 2017, scientists announced that they had directly detected gravitational waves in addition to light from the spectacular collision of two neutron stars, marking the first time that a cosmic event has been viewed in both gravitational waves and light. That event was widely reported as helping usher in an era of multi-messenger astronomy.
UK teams have played important roles in the development and construction of both LIGO and the data analysis which allows the collaboration to pick out the gravitational wave signals. The UK’s contribution to the collaborations is funded by the Science and Technology Facilities Council (STFC).
Last updated: 23 June 2020