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Updated: 2025-10-30
A gravitational wave is a ripple in the fabric of space and time,
created when massive objects such as black holes or neutron stars
accelerate or collide. These waves travel across the Universe at
the speed of light, stretching and squeezing space itself as they
pass. Predicted by Albert Einstein in 1916 as part of his General
Theory of Relativity, gravitational waves were first directly
detected a century later, in 2015, by the LIGO observatory. Their
discovery opened a new way of observing the cosmos — not through
light, but through the vibrations of spacetime — allowing
scientists to study some of the most energetic and mysterious
events in the Universe.
A gravitational wave is a ripple in the fabric of space and time,
created when massive objects such as black holes or neutron stars
accelerate or collide. These waves travel across the Universe at
the speed of light, stretching and squeezing space itself as they
pass. Predicted by Albert Einstein in 1916 as part of his General
Theory of Relativity, gravitational waves were first directly
detected a century later, in 2015, by the LIGO observatory. Their
discovery opened a new way of observing the cosmos — not through
light, but through the vibrations of spacetime — allowing
scientists to study some of the most energetic and mysterious
events in the Universe.
The Einstein Telescope (ET) is a planned European third-generation
gravitational-wave observatory that will take this new field of
astronomy to the next level. It will consist of a triangular
system of underground tunnels, each about 10 kilometres long,
housing ultra-sensitive laser interferometers. By operating deep
underground and at cryogenic temperatures, ET will be able to
detect much weaker signals than current instruments, observing
black hole and neutron star mergers from the farthest reaches of
the cosmos.
The Einstein Telescope will consist of a triangular underground
observatory with sides 10 kilometres long. Each side will host two
laser interferometers arranged in an “X” configuration. By
measuring minute changes in the distance between suspended mirrors
at the ends of these arms — as small as one thousandth of the
diameter of a proton — ET will detect passing gravitational waves.
The design includes two sets of interferometers: one optimized for
low frequencies (using cryogenically cooled mirrors to reduce
thermal noise) and another for high frequencies, allowing the
observatory to cover a broad range of sources and timescales.
The observatory will be built deep underground to minimize the
effects of seismic vibrations and environmental noise. Two
potential sites are currently under study: one in Sardinia (Italy)
and another in the Euregio Meuse-Rhine region, located at the
border of Belgium, the Netherlands, and Germany. The final choice
will depend on detailed geological, environmental, and logistical
evaluations.
The Einstein Telescope will be about ten times more sensitive than
current detectors such as LIGO, Virgo, and KAGRA. This higher
sensitivity will allow scientists to observe thousands of
gravitational-wave events every year, reaching back to the time
when the first stars and galaxies were forming. It will make
possible the precise measurement of neutron star properties, tests
of Einstein’s theory of General Relativity under extreme
conditions, and the search for primordial gravitational waves that
carry information from the earliest moments after the Big Bang.
The Einstein Telescope will also work in close connection with
other astronomical observatories to form part of the global
multimessenger network, linking gravitational-wave detections with
observations of light, neutrinos, and cosmic rays. Such combined
observations will help identify the origins of the most energetic
phenomena in the Universe, from gamma-ray bursts and magnetar
flares to the merging of compact stellar remnants.
A recent ET Collaboration white paper (see
The Science of the Einstein Telescope, arXiv:2503.12263) outlines in detail the scientific reach of ET: across
astrophysics, cosmology, fundamental physics and nuclear matter
under extreme conditions. The document studies both the proposed
triangular single-site and dual L-shaped geometries, and
emphasises how ET will form a key node in the global
multimessenger network — enabling multi-band gravitational-wave
observations and combining them with electromagnetic, neutrino and
cosmic-ray signals. It also highlights the major data-analysis
challenges ahead, given the high event rates and precision
expected for a third-generation detector.
The observatory will be built deep underground to shield it from
surface vibrations and environmental noise. Two possible locations
are currently under study: the Sos Enattos site in Sardinia
(Italy) and the Euregio Meuse-Rhine region on the
Belgium–Netherlands–Germany border. Both offer exceptional
geological stability and low-seismic conditions needed for the
precise measurement of spacetime distortions.
ET will employ innovative technologies such as cryogenically
cooled mirrors, high-power laser systems, and advanced
vibration-isolation systems. These developments will allow an
unprecedented sensitivity, enabling the detection of signals from
the most distant and ancient events in the Universe. More
information is available on the official Einstein Telescope
website.
Researchers from the IFJ PAN, NZ 15 will take part in the
scientific programme of the Einstein Telescope (ET), contributing
to theoretical studies, data analysis methods, and the development
of the multimessenger astrophysics framework that connects
gravitational-wave, neutrino, and cosmic-ray observations.
Within IFJ PAN, the group currently includes researchers with
focuses on neutron star physics and their role as
gravitational-wave sources, exploring the connection between
dense-matter equations of state and observable waveforms. Work is
also done on gravitational waves from eccentric binary systems,
the influence of spin-induced effects, and advanced data analysis
and Fisher matrix techniques used to assess parameter estimation
accuracy for future ET observations.
In the coming years, the team plans to expand its activities by
including an experimental physicist to strengthen the link between
detector technology and astrophysical data analysis.
The opportunities of the Einstein Telescope (EN)