In astronomy and

observational cosmology Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors. Early observations The science of physical cosmology as it is ...

, the BOOMERanG experiment (Balloon Observations Of Millimetric Extragalactic Radiation And Geophysics) was an experiment which measured the

cosmic microwave background radiation In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all space ...

of a part of the sky during three sub-orbital (high-altitude) balloon flights. It was the first experiment to make large, high-fidelity images of the CMB temperature anisotropies, and is best known for the discovery in 2000 that the geometry of the universe is close to flat, with similar results from the competing MAXIMA experiment. By using a telescope which flew at over 42,000 meters high, it was possible to reduce the atmospheric absorption of microwaves to a minimum. This allowed massive cost reduction compared to a satellite probe, though only a tiny part of the sky could be scanned. The first was a test flight over North America in 1997. In the two subsequent flights in 1998 and 2003 the balloon was launched from McMurdo Station in the Antarctic. It was carried by the

Polar vortex A circumpolar vortex, or simply polar vortex, is a large region of cold, rotating air that encircles both of Earth's polar regions. Polar vortices also exist on other rotating, low-obliquity planetary bodies. The term polar vortex can be used to ...

winds in a circle around the

South Pole The South Pole, also known as the Geographic South Pole, Terrestrial South Pole or 90th Parallel South, is one of the two points where Earth's axis of rotation intersects its surface. It is the southernmost point on Earth and lies antipod ...

, returning after two weeks. From this phenomenon the telescope took its name. The BOOMERanG team was led by Andrew E. Lange of

Caltech The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...

and Paolo de Bernardis of the

University of Rome La Sapienza The Sapienza University of Rome ( it, Sapienza – Università di Roma), also called simply Sapienza or the University of Rome, and formally the Università degli Studi di Roma "La Sapienza", is a public research university located in Rome, Ita ...

Instrumentation

The experiment uses

bolometer A bolometer is a device for measuring radiant heat by means of a material having a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley. Principle of operation A bolometer ...

s for radiation detection. These bolometers are kept at a temperature of 0.27

kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phy ...

. At this temperature the material has a very low heat capacity according to the Debye law, thus incoming microwave light will cause a large temperature change, proportional to the intensity of the incoming waves, which is measured with sensitive thermometers. An off-axis 1.3-meter primary mirror focuses the microwaves onto the focal plane, which consist of 16 horns. These horns, operating at 145 GHz, 245 GHz and 345 GHz, are arranged into 8 pixels. Only a tiny fraction of the sky can be seen concurrently, so the telescope must rotate to scan the whole field of view.

Results

Together with experiments like the Saskatoon experiment, TOCO, MAXIMA, and others, the BOOMERanG data from 1997 and 1998 determined the angular diameter distance to the surface of last scattering with high precision. When combined with complementary data regarding the value of

Hubble's constant Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving a ...

, the Boomerang data determined the geometry of the Universe to be flat, supporting the supernova evidence for the existence of

dark energy In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univ ...

. The 2003 flight of Boomerang resulted in extremely high signal-to-noise ratio maps of the CMB temperature anisotropy, and a measurement of the polarization of the CMB.

References

External links

report on the 1998 flightPolarization Sensitive Bolometric Detector
{{CMB_experiments Cosmic microwave background experiments Balloon-borne telescopes Astronomical experiments in the Antarctic