Detector engineers install hardware upgrades in preparation for the now month old Advanced LIGO's third observing run.(Credit: LIGO/Caltech/MIT/Jeff Kissel)
Massive collisions in the Universe between black holes or dead stars appear to happen very frequently as, following the latest switching on of the three upgraded detectors, scientists have detected gravitational waves emanating from the collision of two neutron stars, and another that could be the first evidence of neutron star-black hole collision.
“These two new triggers are further evidence that our universe regularly rings with the aftershocks of colossal astronomical events,” said Professor Sheila Rowan, Director of the University of Glasgow’s Institute for Gravitational Research. “We’d been deaf to those sounds before the detectors equipped us with the opportunity to hear them, and each event gives invaluable new data points to expand our understanding of our cosmos.”
UK scientists and engineers play key roles in the construction and operation of the Laser Interferometer Gravitational-Wave Observatory (LIGO), which runs two detectors in the United States. A third detector named Virgo is operated by a European collaboration and is based in Italy.
On 25 April LIGO and Virgo detected gravitational waves from what appears to be a collision between two neutron stars about 500 million light years from Earth. Neutron stars are the dense remnants of massive exploded stars. Just one day later, the network registered another event about 1.2 billion light-years away and initial analysis suggests it might have been the collision of a neutron star and black hole.
Professor Mark Hannam, Director of Cardiff University’s Gravity Exploration Institute said: “Yet again the LIGO and Virgo detectors have surpassed expectations. Our most optimistic estimates were for a detection every week, and the first month of the run gave us five candidates.”
Professor Alberto Vecchio, Director of the Institute of Gravitational Wave Astronomy, University of Birmingham, said: “LIGO-Virgo have got off to a flying start in the new observing run. We are busy following up several gravitational-wave detection candidates from binary systems of black holes and neutron stars. If the instruments continue to perform as they’ve done so far, it’s going to be many sleepless nights of hard work to tease out from the data the full richness of information from these intriguing cosmic collisions."
While neutron star collisions cause gravitational waves, their impacts also release light across the electromagnetic spectrum. In 2017, LIGO-Virgo’s first-ever detection of a gravitational wave from a neutron star collision was also observed by many conventional telescopes. This time, telescopes around the world once again raced to track the sources and pick up the light expected to arise from these mergers. Hundreds of astronomers eagerly pointed telescopes at patches of sky suspected to house the signal sources. However, at this time, neither of the sources has been pinpointed.
These new results join the growing list of possible gravitational-wave detections since LIGO and Virgo resumed operations last month.
Professor Andreas Freise, Deputy Director, Institute of Gravitational Wave Astronomy, University of Birmingham said: “What a fantastic start! We had anticipated that LIGO and Virgo would observe many new signals during this observation run. It is very exciting to see nature providing us with several new signals in the first month already, fulfilling our earlier predictions.”
The discoveries come just weeks after LIGO and Virgo were turned back on. The twin detectors of LIGO—one in Washington and one in Louisiana—along with Virgo, located at the European Gravitational Observatory (EGO) in Italy, resumed operations 1 April after undergoing a series of upgrades to increase their sensitivities to gravitational waves — ripples in space and time. Each detector now surveys larger volumes of the universe than before, searching for extreme events such as smash-ups between black holes and neutron stars.
Dr Vivien Raymond, from Cardiff University’s Gravity Exploration Institute, said: "LIGO-Virgo's third observing run has already proven to be more interesting than we expected, barely a month after it started. It's exciting to think about the next surprises for us to discover in the Universe."
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.
More Information about the LIGO-Virgo collaborations:
LIGO is funded by NSF and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. 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) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. Nearly 1300 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 the LIGO site.
The Virgo Collaboration is currently composed of approximately 350 scientists, engineers, and technicians from about 70 institutes from 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 members 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.
More information on Gravitational Waves
Since the detectors first started operation in September 2015, the LIGO and Virgo Collaborations, which include the Universities of Birmingham, Cardiff and Glasgow and also the University of Strathclyde, have completed two observation runs. During these runs they have detected gravitational waves from a total of ten stellar-mass binary black hole mergers – compact objects likely formed by the gravitational collapse of massive stars. They have also detected one binary neutron star coalescence – generated by two neutron stars spiraling into each other.
Quelle: UK Science and Technology Facilities Council