MiniGrail
Encyclopedia
MiniGRAIL is an instrument that is designed to detect gravitational wave
s. The MiniGRAIL is the first such detector to use a spherical design. It is located at Leiden University
in the Netherlands
. The project is being managed by the Kamerlingh Onnes Laboratory. A team from the Department of Theoretical Physics of the University of Geneva
, Switzerland
, is also heavily involved.
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 expected to be compact objects such as neutron star
s and black hole
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.
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
atom
), 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% aluminum. 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
.
Tests at temperatures of 5 K showed the detector to have 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 being built in São Paulo
, which will strongly increase the chances of detection by looking at coincidences.
Gravitational wave
In physics, gravitational waves are theoretical ripples in the curvature of spacetime which propagates as a wave, traveling outward from the source. Predicted to exist by Albert Einstein in 1916 on the basis of his theory of general relativity, gravitational waves theoretically transport energy as...
s. The MiniGRAIL is the first such detector to use a spherical design. It is located at Leiden University
Leiden University
Leiden University , located in the city of Leiden, is the oldest university in the Netherlands. The university was founded in 1575 by William, Prince of Orange, leader of the Dutch Revolt in the Eighty Years' War. The royal Dutch House of Orange-Nassau and Leiden University still have a close...
in the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
. The project is being managed by the Kamerlingh Onnes Laboratory. A team from the Department of Theoretical Physics of the University of Geneva
University of Geneva
The University of Geneva is a public research university located in Geneva, Switzerland.It was founded in 1559 by John Calvin, as a theological seminary and law school. It remained focused on theology until the 17th century, when it became a center for Enlightenment scholarship. In 1873, it...
, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
, is also heavily involved.
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 expected to be compact objects such as neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
s and black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
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.
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
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
(the nucleus of a hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
), 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% aluminum. 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
Dilution refrigerator
A dilution refrigerator is a cryogenic device first proposed by Heinz London. Its refrigeration process uses a mixture of two isotopes of helium: helium-3 and helium-4...
.
Tests at temperatures of 5 K showed the detector to have 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 being built in São Paulo
São Paulo
São Paulo is the largest city in Brazil, the largest city in the southern hemisphere and South America, and the world's seventh largest city by population. The metropolis is anchor to the São Paulo metropolitan area, ranked as the second-most populous metropolitan area in the Americas and among...
, which will strongly increase the chances of detection by looking at coincidences.