The Advanced Thin Ionization Calorimeter (ATIC) is a

balloon A balloon is a flexible bag that can be inflated with a gas, such as helium, hydrogen, nitrous oxide, oxygen, and air. For special tasks, balloons can be filled with smoke, liquid water, granular media (e.g. sand, flour or rice), or light so ...

-borne instrument flying in the

stratosphere The stratosphere () is the second layer of the atmosphere of the Earth, located above the troposphere and below the mesosphere. The stratosphere is an atmospheric layer composed of stratified temperature layers, with the warm layers of air ...

over

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...

to measure the energy and composition of

cosmic rays Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

. ATIC was launched from

McMurdo Station McMurdo Station is a United States Antarctic research station on the south tip of Ross Island, which is in the New Zealand-claimed Ross Dependency on the shore of McMurdo Sound in Antarctica. It is operated by the United States through the Unit ...

for the first time in December 2000 and has since completed three successful flights out of four.

Working principle

The detector uses the principle of

ionization Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...

calorimetry In chemistry and thermodynamics, calorimetry () is the science or act of measuring changes in ''state variables'' of a body for the purpose of deriving the heat transfer associated with changes of its state due, for example, to chemical reacti ...

: several layers of the

scintillator A scintillator is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate (i.e. re-emit the absorbed ...

bismuth germanate Bismuth germanium oxide or bismuth germanate is an inorganic chemical compound of bismuth, germanium and oxygen. Most commonly the term refers to the compound with chemical formula (BGO), with the cubic evlitine crystal structure, used as a sci ...

emit light as they are struck by particles, allowing to calculate the particles' energy. A

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

matrix is used to determine the particles'

electrical charge Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...

Collaborators

The project is an international collaboration of researchers from

Louisiana State University Louisiana State University (officially Louisiana State University and Agricultural and Mechanical College, commonly referred to as LSU) is a public land-grant research university in Baton Rouge, Louisiana. The university was founded in 1860 nea ...

University of Maryland, College Park The University of Maryland, College Park (University of Maryland, UMD, or simply Maryland) is a public land-grant research university in College Park, Maryland. Founded in 1856, UMD is the flagship institution of the University System of Mary ...

Marshall Space Flight Center The George C. Marshall Space Flight Center (MSFC), located in Redstone Arsenal, Alabama (Huntsville postal address), is the U.S. government's civilian rocketry and spacecraft propulsion research center. As the largest NASA center, MSFC's first ...

Purple Mountain Observatory The Purple Mountain Observatory (), also known as Zijinshan Astronomical Observatory is an astronomical observatory located on the Purple Mountain in the east of Nanjing. Description The Purple Mountain Observatory was established in 1934 fun ...

in China,

Moscow State University M. V. Lomonosov Moscow State University (MSU; russian: Московский государственный университет имени М. В. Ломоносова) is a public research university in Moscow, Russia and the most prestigious ...

in Russia and

Max Planck Institute for Solar System Research The Max Planck Institute for Solar System Research (abbreviation: MPS; german: Max-Planck-Institut für Sonnensystemforschung) is a research institute in astronomy and astrophysics located in Göttingen, Germany, where it relocated in February 201 ...

in Germany. ATIC is supported in the United States by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

and flights are conducted under the auspices of the Balloon Program Office at

Wallops Flight Facility Wallops Flight Facility (WFF) is a rocket launch site on Wallops Island on the Eastern Shore of Virginia, United States, just east of the Delmarva Peninsula and approximately north-northeast of Norfolk. The facility is operated by the Goddard ...

by the staff of the

Columbia Scientific Balloon Facility The Columbia Scientific Balloon Facility (CSBF) (established in 1961, formerly known as the National Scientific Balloon Facility (NSBF)) is a NASA facility responsible for providing launch, tracking and control, airspace coordination, telemetry ...

. Antarctic logistics are provided by the

National Science Foundation The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National I ...

and its contractor

Raytheon Raytheon Technologies Corporation is an American multinational aerospace and defense conglomerate headquartered in Arlington, Virginia. It is one of the largest aerospace and defense manufacturers in the world by revenue and market capitaliza ...

Polar Services Corporation. The principal investigator for ATIC is John Wefel of Louisiana State University. ATIC closeup

Results

In November 2008, researchers published in ''

Nature Nature, in the broadest sense, is the physics, physical world or universe. "Nature" can refer to the phenomenon, phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. ...

'' the finding of a surplus of high energy

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

s. During a 5-week observatory period in 2000 and 2003, ATIC counted 70 electrons with energies in the range 300–800 GeV; these electrons were in excess of those expected from the galactic background. The source of these electrons is unknown, but it is assumed to be relatively close, no more than about 3000

lightyear A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s away, since high energy electrons rapidly lose energy as they travel through the galactic magnetic field and collide with photons. The electrons could originate from a nearby

pulsar A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Ea ...

or other astrophysical object, but the researchers were not able to identify a fitting object. According to another conjecture, the electrons result from collisions of

Dark Matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...

particles, for example

WIMP Wimp, WIMP, or Wimps may refer to: Science and technology * Weakly interacting massive particle, a hypothetical particle of dark matter * WIMP (computing), the "window, icon, menu, pointer" paradigm * WIMP (software bundle), the web stack of Wind ...

Kaluza-Klein particles of mass near 620 GeV.Mysterious electrons may be sign of dark matter
''New Scientist'', 19 November 2008

Related data from other experiments

Earlier in the year, the satellite

PAMELA Pamela may refer to: *''Pamela; or, Virtue Rewarded'', a novel written by Samuel Richardson in 1740 *Pamela (name), a given name and, rarely, a surname *Pamela Spence, a Turkish pop-rock singer. Known as her stage name "Pamela" * MSC ''Pamela'', ...

had found excess

positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 '' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. When a positron collides ...

s (the antiparticle of the electron) in the cosmic ray signal, also believed to originate from dark matter interactions. ATIC cannot distinguish between electrons and positrons, so it is possible that the two results are compatible. On the other hand, in November 2008 the Milagro experiment reported cosmic ray "hotspots" in the sky, possibly supporting astrophysical objects as sources of the surplus electrons. In May 2009, observations by the Fermi space telescope were reported which did not support the spike of high-energy electrons seen by ATIC.Dark matter signal recedes into the shadows
''New Scientist'', 7 May 2009

References

External links

from the Department of Physics and Astronomy at Louisiana State University

(Antarctica 2000/2001)

(Antarctica 2002/2003)

(Antarctica 2005)

(Antarctica 2007/2008) {{Dark matter Cosmic-ray experiments Science and technology in Antarctica Balloon-borne experiments Experiments for dark matter search