Colliding stars

A new encounter with the universe is how the spectacular observation of two colliding neutron stars last August was described. And the beginning of a new research field: multi-messenger astronomy.

Text: Mariëtte Huisjes

Three detectors and seventy telescopes were involved, both on Earth and in space, but then the outcome was an observation that turned the scientific world upside down. Gravitational waves – ripples in spacetime – and light caused by a collision between two neutron stars: small ultracompact remnants of massive stars that exploded in a supernova explosion.

Two colliding neutron stars (credits: Sonoma State University / Aurore Simonnet)

On 17 August at 14:41 CET, the two American LIGO detectors in Hanford (Washington) and Livingston (Louisiana) were the first to detect a powerful gravitational wave. Information from the European Virgo detector near the Italian city of Pisa was vital for localising the source. This enabled astronomers to point their telescopes in the right direction to make subsequent observations. The discovery is a textbook case of successful international collaboration in science. Dutch physicists and astronomers were also directly involved in the observation, for example via the National Institute for Subatomic Physics Nikhef, a collaboration between NWO and five Dutch universities.

Listening to the universe

It is the first time that a cosmic event has been observed simultaneously through two types of signals. The combination of the gravitational waves detected and the observations in the electromagnetic spectrum (light) provides a completely new way of “listening” to the universe. It has created high expectations for even more exciting discoveries in the future. The three detectors that played the lead role in the discovery last August, LIGO and Virgo, are currently receiving an upgrade to improve their sensitivity. The technology for a new measurement facility is also being worked on; a facility that will be able to detect gravitational waves with extreme accuracy. This Einstein Telescope will consist of a subterranean triangle of ten-kilometre-long arms with measurement equipment that will be able to explore volumes in our universe 1000 times larger than is currently possible. The location for the Einstein Telescope will be decided in 2021. The border region around South Limburg is one of the contenders.