Virgo (gravitational wave detector)
Virgo is a Franco-Italian gravitational wave detector , the core of which is a Michelson interferometer with arms each three kilometers long.
The detector was in operation from 2007 to 2011. It was then taken out of service to further increase sensitivity. After delays, the new, more sensitive Advanced Virgo detector went into operation in August 2017.
Technical specifications
The Advanced Virgo is located on the premises of the European Gravitational Wave Observatory (EGO) in Santo Stefano a Macerata ( Cascina ) in Italy, in the same facility in which the previous Virgo detector was located.
The interferometer consists of two arms with a length of 3 km each, which are arranged at right angles to each other. These arms are evacuated tubes with a diameter of 1.2 m. The laser light is thrown back and forth several times in this interferometer, creating an interferometer with an effective arm length of around 100 km. The mirrors used reflect 99.999% of the infrared laser light that hits them. The power of the laser is 200 W, but the laser beam is superimposed several times, so that a much higher effective power can be achieved. The wavelength of the emitted light is 1064 nm. Both the power of the laser and the frequency of the light must be as constant as possible.
The Virgo detector covers the frequency range from around 10 Hz to 10 kHz. The lower detection limit of this detector is at amplitudes in the order of 10 −22 . Thus, the detector should be able to measure gravitational waves that originate from massive binary star systems or supernovae . For the observation of a collision of a binary star system, the range of the detector is about 300 million light years . Such an event within reach is expected a few times a month.
functionality
When a gravitational wave passes through the detector, the length of the arms of the interferometer changes. This leads to a phase shift between the laser beams in the two arms and the interference pattern that arises after the two beams are superimposed changes. The change in this interference pattern can be measured.
history
In 1989 the project application for Virgo was made and in 1994 it was accepted. The planning was completed in 1997. The building was completed in 2003; then the detector was calibrated and tested. Data was collected for the first time between 2007 and 2011. The detector has since been improved, which was originally supposed to be completed by the end of 2015. Then data should be collected again from 2016 to 2020.
One of the directors was the French Alain Brillet . On the Italian side, Adalberto Giazotto was one of the leading scientists.
The old Virgo detector had a 10 times lower sensitivity, so its lower detection limit was amplitudes of 10 −21 . As a result, the range for the observation was only 1/10 as large and consequently the observable volume was only 1/1000 as large. While several observable events are now expected per month, it was once every 20 to 50 years.
The higher accuracy of the Advanced Virgo was achieved on the one hand by improving the mirrors and the vacuum and on the other hand by using a laser with 10 times the power.
There is a close cooperation with other gravitational wave detectors; the data are collected and analyzed jointly and joint publications are issued.
On August 14, 2017 at 12:30:43 p.m. CEST, the two American Advanced Ligo observatories, which had detected all three previously registered gravitational waves, as well as the Franco-Italian Advanced Virgo detector observed the GW170814 signal , which was transmitted by the merging of two black holes was created. The cooperation of all three observatories increased the accuracy by a factor of ten. The polarization of the gravitational waves was also observed for the first time. Advanced Virgo began observing for the first time on August 1st.
See also
swell
- Description of the Virgo detector
- Description of the advanced VIRGO
- History and cooperation partners
- Gravitational Wave Detectors and Sources
Web links
- Description on the homepage of the European Gravitational Wave Observatory
- Homepage of the Virgo collaboration
Individual evidence
- ^ Reply to a report in Science Magazine (PDF) Retrieved April 15, 2017.
- ↑ Michelle Starr, IT'S OFFICIAL: Gravitational Waves Were Just Detected With The Greatest Precision Ever, Science Alert , September 27, 2017
Coordinates: 43 ° 37 ′ 53 ″ N , 10 ° 30 ′ 17 ″ E