Magnetar
Encyclopedia
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...
with an extremely powerful magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
, the decay of which powers the emission of copious high-energy electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
, particularly X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s and gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s. The theory regarding these objects was proposed by Robert Duncan and Christopher Thompson in 1992, but the first recorded burst of gamma rays thought to have been from a magnetar was detected on March 5, 1979. During the following decade, the magnetar hypothesis has become widely accepted as a likely explanation for soft gamma repeater
Soft gamma repeater
A soft gamma repeater is an astronomical object which emits large bursts of gamma-rays and X-rays at irregular intervals. It is conjectured that they are a type of magnetar or, alternatively, neutron stars with fossil disks around them....
s (SGRs) and anomalous X-ray pulsar
Anomalous X-ray pulsar
Anomalous X-ray Pulsars are now widely believed to be magnetars—young, isolated, highly magnetized neutron stars. These energetic X-ray pulsars are characterized by slow rotation periods of ~2–12 seconds and large magnetic fields of ~1013–1015 gauss . There are currently 9 known and 1 candidate...
s (AXPs).
Description
Little is known about the physical structure of magnetars because none are sufficiently close to EarthEarth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
to facilitate study. Like other 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, magnetars are around 20 kilometres (12.4 mi) in diameter but have a greater mass than the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. The density of a magnetar is such that a thimble
Thimble
A thimble is a small hard pitted cup worn for protection on the finger that pushes the needle in sewing.The earliest known thimble was Roman and was found at Pompeii. Made of bronze, its creation has been dated to the 1st century AD...
ful of its substance, sometimes referred to as neutronium
Neutronium
Neutronium is a proposed name for a substance composed purely of neutrons. The word was coined by scientist Andreas von Antropoff in 1926 for the conjectured "element of atomic number zero" that he placed at the head of the periodic table...
, would have a mass of over 100 million tons. Magnetars are differentiated from other neutron stars by having even stronger magnetic fields, and rotating comparatively slowly, with most magnetars completing a rotation once every one to ten seconds. compared to less than one second for a typical neutron star. This magnetic field gives rise to very strong and characteristic bursts of X-rays and gamma rays. The active life of a magnetar is short. Their strong magnetic fields decay after about 10,000 years, after which activity and strong X-ray emission cease. Given the number of magnetars observable today, one estimate puts the number of inactive magnetars in the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
at 30 million or more.
Starquakes triggered on the surface of the magnetar cause great volatility in the star and the magnetic field which encompasses it, often leading to extremely powerful gamma ray flare emissions which have been recorded on Earth in 1979, 1998, and 2004.
Magnetic field
Magnetars are primarily characterized by their extremely powerful magnetic field, which can often reach the order of ten gigateslasTesla (unit)
The tesla is the SI derived unit of magnetic field B . One tesla is equal to one weber per square meter, and it was defined in 1960 in honour of the inventor, physicist, and electrical engineer Nikola Tesla...
. These magnetic fields are hundreds of millions of times stronger than any man-made magnet, and quadrillions of times more powerful than the field surrounding Earth
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...
. Earth has a geomagnetic field of 30–60 microteslas, and a neodymium-based, rare-earth magnet
Neodymium magnet
A neodymium magnet , the most widely-used type of rare-earth magnet, is a permanent magnet made from an alloy of neodymium, iron, and boron to form the Nd2Fe14B tetragonal crystalline structure. Developed in 1982 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest...
has a field of about 1 tesla, with a magnetic energy density of 4.0×105 J/m3. A 10 gigatesla field, by contrast, has an energy density of 4.0×1025 J/m3, with an E/c2 mass density >104 times that of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
. The magnetic field of a magnetar would be lethal even at a distance of 1000 km, tearing tissues due to the diamagnetism
Diamagnetism
Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Specifically, an external magnetic field alters the orbital velocity of electrons around their nuclei, thus changing the...
of water. At a distance halfway to the moon, a magnetar could strip information from all credit card
Credit card
A credit card is a small plastic card issued to users as a system of payment. It allows its holder to buy goods and services based on the holder's promise to pay for these goods and services...
s on Earth. , they are the most magnetic objects ever detected in the universe.
As described in the February 2003 Scientific American
Scientific American
Scientific American is a popular science magazine. It is notable for its long history of presenting science monthly to an educated but not necessarily scientific public, through its careful attention to the clarity of its text as well as the quality of its specially commissioned color graphics...
cover story, remarkable things happen within a magnetic field of magnetar strength. "X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
photons readily split in two or merge together. The vacuum itself is polarized, becoming strongly birefringent, like a calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
crystal. 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...
s are deformed into long cylinders thinner than the quantum-relativistic de Broglie wavelength of an electron." In a field of about 105 teslas atomic orbital
Atomic orbital
An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...
s deform into rod shapes. At 1010 teslas, a hydrogen atom
Hydrogen atom
A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively-charged proton and a single negatively-charged electron bound to the nucleus by the Coulomb force...
becomes a spindle 200 times narrower than its normal diameter. Currently, the mechanism which generates such strong magnetic fields, if they exist, is unknown.
Formation
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
, a star collapses to a neutron star, its magnetic field increases dramatically in strength. Halving a linear dimension increases the magnetic field fourfold. Duncan and Thompson calculated that, when the spin, temperature and magnetic field of a newly formed neutron star falls into the right ranges, a dynamo mechanism
Dynamo theory
In geophysics, dynamo theory proposes a mechanism by which a celestial body such as the Earth or a star generates a magnetic field. The theory describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time...
could act, converting heat and rotational energy into magnetic energy, and increasing the magnetic field, normally an already enormous 108 tesla
Tesla (unit)
The tesla is the SI derived unit of magnetic field B . One tesla is equal to one weber per square meter, and it was defined in 1960 in honour of the inventor, physicist, and electrical engineer Nikola Tesla...
s to more than 1011 teslas (or 1015 gauss
Gauss (unit)
The gauss, abbreviated as G, is the cgs unit of measurement of a magnetic field B , named after the German mathematician and physicist Carl Friedrich Gauss. One gauss is defined as one maxwell per square centimeter; it equals 1 tesla...
). The result is a magnetar. It is estimated that about one in ten supernova explosions results in a magnetar rather than a more standard neutron star or pulsar
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
.
1979 discovery
On March 5, 1979, a few months after the successful dropping of satellites into the atmosphere of VenusVenus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
, the two Soviet spacecraft that were then drifting through the solar system were hit by a blast of gamma ray radiation at approximately 10:51 EST. This contact raised the radiation readings on both the probes from a normal 100 counts per second to over 200,000 counts a second, in only a fraction of a millisecond.
This burst of gamma rays quickly continued to spread. Eleven seconds later, Helios 2
Helios probes
Helios-A and Helios-B , were a pair of probes launched into heliocentric orbit for the purpose of studying solar processes. A joint venture of the Federal Republic of Germany and NASA, the probes were launched from the John F. Kennedy Space Center at Cape Canaveral, Florida, on Dec. 10, 1974,...
, a NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
probe, which was in orbit around the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, was saturated by the blast of radiation. It soon hit Venus, and the Pioneer Venus Orbiter's detectors were overcome by the wave. Seconds later, Earth received the wave of radiation, where the powerful output of gamma rays inundated the detectors of three U.S. Department of Defense Vela satellites
Vela (satellite)
Vela was the name of a group of satellites developed as the Vela Hotel element of Project Vela by the United States to monitor compliance with the 1963 Partial Test Ban Treaty by the Soviet Union, and other nuclear-capable states. It means vigil or "watch" in Spanish.Vela started out as a small...
, the Soviet Prognoz 7 satellite
Prognoz SO-M
Prognoz SO-M was a Soviet scientific research satellite programme. Ten Prognoz satellites were launched between 14 April 1972 and 26 April 1985, by Molniya-M carrier rockets. The satellites were placed in High Earth orbits...
, and the Einstein Observatory
Einstein Observatory
Einstein Observatory was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories...
. Just before the wave exited the solar system, the blast also hit the International Sun-Earth Explorer. This extremely powerful blast of gamma ray radiation constituted the strongest wave of extra-solar gamma rays ever detected; it was over 100 times more intense than any known previous extra-solar burst. Because gamma rays travel at the speed of light and the time of the pulse was recorded by several distant spacecraft as well as on Earth, the source of the gamma radiation could be calculated to an accuracy of about 2 arcseconds. The direction of the source corresponded with the remnants of a star that had gone supernova around 3000 B.C.
Recent discoveries
On February 21, 2008 it was announced that NASA and researchers at McGill UniversityMcGill University
Mohammed Fathy is a public research university located in Montreal, Quebec, Canada. The university bears the name of James McGill, a prominent Montreal merchant from Glasgow, Scotland, whose bequest formed the beginning of the university...
had discovered a neutron star with the properties of a radio pulsar which emitted some magnetically-powered bursts, like a magnetar. This suggests that magnetars are not merely a rare type of pulsar
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
but may be a (possibly reversible) phase in the lives of some pulsars. On September 24, 2008, ESO
ESO
ESO, as a three-letter abbreviation, may stand for:* European Southern Observatory* Ensemble Studios Online* English Symphony Orchestra* Edmonton Symphony Orchestra* Executive Stock Options...
announced what it believed was the first optically active magnetar-candidate yet discovered, using ESO's Very Large Telescope
Very Large Telescope
The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...
. The newly discovered object was designated SWIFT J195509+261406.
Known magnetars
- SGR 1806-20SGR 1806-20|- style="vertical-align: top;"| Distance | 50,000 light-years SGR 1806-20 is a magnetar, a particular type of neutron star. It has been identified as a soft gamma repeater. SGR 1806-20 is located about 14.5 kiloparsecs from Earth on the far side of our Milky Way galaxy in the constellation of...
, located 50,000 light-years from Earth on the far side of our Milky Way galaxy in the constellation of SagittariusSagittarius (constellation)Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
. - SGR 1900+14SGR 1900+14|- style="vertical-align: top;"| Distance | SGR 1900+14, is located in the constellation of Aquila about 45,000 light-years away. It is an example of an intensely magnetic star, known as a magnetar, which is thought to arise from a fairly recent supernova explosion; only four are known to exist for...
, located 20,000 light-years away in the constellation AquilaAquila (constellation)Aquila is a stellar constellation. Its name is Latin for 'eagle' and it is commonly represented as such. In mythology, Aquila was owned by the Roman god Jupiter and performed many tasks for him....
. After a long period of low emissions (significant bursts only in 1979 and 1993) it became active in May-August 1998, and a burst detected on August 27, 1998 was of sufficient power to force NEAR ShoemakerNEAR ShoemakerThe Near Earth Asteroid Rendezvous - Shoemaker , renamed after its 1996 launch in honor of planetary scientist Eugene M. Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a...
to shut-down to prevent damage and to saturate instruments on BeppoSAXBeppoSAXBeppoSAX was an Italian–Dutch satellite for X-ray astronomy which played a crucial role in resolving the origin of gamma-ray bursts , the most energetic events known in the universe...
, WINDWINDThe Global Geospace Science WIND satellite is a NASA science spacecraft launched at 04:31:00 EST on November 1, 1994 from launch pad 17B at Cape Canaveral Air Force Station in Merritt Island, Florida aboard a McDonnell Douglas Delta II 7925-10 rocket. WIND was designed and manufactured by Martin...
and RXTE. On May 29, 2008, NASA's Spitzer telescope discovered a ring of matter around this magnetar. It is thought that this ring formed in the 1998 burst. - SGR 0501+4516SGR 0501+4516SGR 0501+4516 is one of 15 known magnetars, or soft gamma repeaters , and is an ancient stellar remnant. It is located approximately 15,000 light years from earth and has a magnetic field 100 trillion times stronger than the Earth’s.-Discovery:...
was discovered on Aug. 22, 2008 - 1E 1048.1-5937AXP 1E 1048-59Anomalous X-ray pulsar 1E 1048.1-5937 was the first AXP ever observed to emit an SGR-like X-ray burst....
, located 9,000 light-years away in the constellation CarinaCarina (constellation)Carina is a constellation in the southern sky. Its name is Latin for the keel of a ship, and it was formerly part of the larger constellation of Argo Navis until that constellation was divided in three.-Stars:...
. The original star, from which the magnetar formed, had a mass 30 to 40 times that of the SunSunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
., ESO reports identification of an object which it has initially identified as a magnetar, SWIFT J195509+261406, originally identified by a gamma-ray burst (GRB 070610) - CXO J164710.2-455216CXO J164710.2-455216CXO J164710.2-455216 is an anomalous X-ray pulsar in the massive galactic open cluster Westerlund 1. It is the brightest X-ray source in the cluster, and was discoveredin 2005 in observations made by the Chandra X-ray observatory...
, located in the massive galactic cluster Westerlund 1Westerlund 1Westerlund 1 is a compact young star cluster in the Milky Way galaxy, about 3.5–5 kpc away from Earth. In fact, it is the most massive compact young star cluster known in the entire Local Group of galaxies...
, which formed from a star with a mass in excess of 40 solar masses.
A full listing is given in the McGill
McGill University
Mohammed Fathy is a public research university located in Montreal, Quebec, Canada. The university bears the name of James McGill, a prominent Montreal merchant from Glasgow, Scotland, whose bequest formed the beginning of the university...
SGR/AXP Online Catalog.
External links
- Recording (and animation) of XTE J1810-197.
- Creation of magnetars solved Formed when the biggest stars explode
- NASA: "Magnetar" discovery solves 19-year-old mystery Citat: "...suggested a magnetic field strength of about 800 trillion [g]auss...").
- Robert C. Duncan, University of Texas at Austin: 'Magnetars', Soft Gamma Repeaters & Very Strong Magnetic Fields
- NASA Astrophysics Data System (ADS): Duncan & Thompson, Ap.J. 392, L9) 1992
- NASA Astrophysics Data System (ADS): Katz, J. I., Ap.J. 260, 371 (1982)
- NASA ADS, 1999: Discovery of a Magnetar Associated with the Soft Gamma Repeater SGR 1900+14
- Chryssa Kouveliotou, Robert C. Duncan, and Christopher Thompson, "Magnetars," Scientific American, Feb. 2003, pp. 34-41 (PDF)
- Strange Pulsing Star Puzzles Astronomers - A magnetar found to emit radio waves, contrary to previous theories.
- 04/04/07: X-ray Satellites Catch Magnetar in Gigantic Stellar 'Hiccup'
- "Magnetars" (Paper on magnetar formation from March 1995 conference proceedings, suggesting that AXPs are magnetars.)