MiniGRAIL was a type of Resonant Mass Antenna,
which is a massive sphere that used to detect
gravitational wave
Gravitational waves are waves of the intensity of gravity generated by the accelerated masses of an orbital binary system that propagate as waves outward from their source at the speed of light. They were first proposed by Oliver Heaviside in ...
s. The MiniGRAIL was the first such detector to use a spherical design. It is located at
Leiden University in the
Netherlands
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. The project was managed by the
Kamerlingh Onnes Laboratory.
A team from the Department of Theoretical Physics of the
University of Geneva
The University of Geneva (French: ''Université de Genève'') is a public research university located in Geneva, Switzerland. It was founded in 1559 by John Calvin as a theological seminary. It remained focused on theology until the 17th centur ...
,
Switzerland, was also heavily involved. The project was terminated in 2005.
Gravitational waves are a type of radiation that is emitted by objects that have mass and are undergoing acceleration. The strongest sources of gravitational waves are suspected to be
compact object
In astronomy, the term compact star (or compact object) refers collectively to white dwarfs, neutron stars, and black holes. It would grow to include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects h ...
s such as
neutron star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...
s and
black hole
A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can defo ...
s. This detector may be able to detect certain types of instabilities in rotating single and binary neutron stars, and the merger of small black holes or neutron stars.
Design
A spherical design has the benefit of being able to detect gravitational waves arriving from any direction, and it is sensitive to polarization.
When gravitation waves with frequencies around 3,000 Hz pass through the MiniGRAIL ball, it will vibrate with displacements on the order of 10
−20 m. For comparison, the cross-section of a single
proton (the nucleus of a
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
atom
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons.
Every solid, liquid, gas ...
), is 10
−15 m (1 fm).
To improve sensitivity, the detector was intended to operate at a temperature of 20 mK.
The original antenna for the MiniGRAIL detector was a 68 cm diameter sphere made of an alloy of copper with 6% aluminium. This sphere had a mass of 1,150 kg and resonated at a frequency of 3,250 Hz. It was isolated from vibration by seven 140 kg masses. The
bandwidth of the detector was expected to be ±230 Hz.
During the casting of the sphere, a crack appeared that reduced the quality to unacceptable levels. It was replaced by a 68 cm sphere with a mass of 1,300 kg. This was manufactured by ItalBronze in Brazil. The larger mass lowered the resonant frequencies by about 200 Hz. The sphere is suspended from stainless steel cables to which springs and masses are attached to dampen vibrations. Cooling is accomplished using a
dilution refrigerator
A 3He/4He dilution refrigerator is a cryogenic device that provides continuous cooling to temperatures as low as 2 mK, with no moving parts in the low-temperature region. The cooling power is provided by the heat of mixing of the Hel ...
.
Tests at temperatures of 5 K showed that the detector had a peak strain sensitivity of at a frequency of 2942.9 Hz. Over a bandwidth of 30 Hz, the strain sensitivity was more than . This sensitivity is expected to improve by an order of magnitude when the instrument is operating at 50 mK.
A similar detector named "
Mario Schenberg
is a character created by Japanese video game designer Shigeru Miyamoto. He is the title character of the ''Mario'' franchise and the mascot of Japanese video game company Nintendo. Mario has appeared in over 200 video games since his creat ...
" is located in
São Paulo
São Paulo (, ; Portuguese for 'Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the Ga ...
. The co-operation of the detectors strongly increase the chances of detection by looking at coincidences.
References
External links
MiniGRAIL on the internet
{{coord missing, Netherlands
Gravitational-wave telescopes
Astronomical observatories in the Netherlands