A flare star is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

that can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to

solar flare A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other sol ...

s in that they are due to the magnetic energy stored in the

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s' atmospheres. The brightness increase is across the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...

, from

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

s to

radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (sho ...

s. The first known flare stars ( V1396 Cygni and

AT Microscopii AT Microscopii is a binary star system located at a distance of from the Sun in the constellation of Microscopium. Both members are flare stars, meaning they are red dwarf stars that undergo random eruptions that increase their brigh ...

) were discovered in 1924. However, the best-known flare star is

UV Ceti Luyten 726-8, also known as Gliese 65, is a binary star system that is one of Earth's nearest neighbors, at about 8.7 light years from Earth in the constellation Cetus. The two component stars are both flare stars with the variable sta ...

, first observed to flare in 1948. Today similar flare stars are classified as UV Ceti type

s (using the abbreviation UV) in variable star catalogs such as the

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and thi ...

. Most flare stars are dim

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. ...

s, although recent research indicates that less massive

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

s might also be capable of flaring. The more massive RS Canum Venaticorum variables (RS CVn) are also known to flare, but it is understood that these flares are induced by a companion star in a binary system which causes the

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

to become tangled. Additionally, nine stars similar to the Sun had also been seen to undergo flare events prior to the flood of superflare data from the

Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...

observatory. It has been proposed that the mechanism for this is similar to that of the RS CVn variables in that the flares are being induced by a companion, namely an unseen Jupiter-like planet in a close orbit.

Nearby flare stars

Flare stars are intrinsically faint, but have been found to distances of 1,000

light year 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 from Earth. On April 23, 2014,

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, succeedin ...

's Swift satellite detected the strongest, hottest, and longest-lasting sequence of stellar flares ever seen from a nearby red dwarf, DG Canum Venaticorum. The initial blast from this record-setting series of explosions was as much as 10,000 times more powerful than the largest

ever recorded.

Proxima Centauri

The Sun's nearest stellar neighbor

Proxima Centauri Proxima Centauri is a small, low-mass star located away from the Sun in the southern constellation of Centaurus. Its Latin name means the 'nearest tarof Centaurus'. It was discovered in 1915 by Robert Innes and is the nearest-k ...

is a flare star that undergoes occasional increases in brightness because of magnetic activity. The star's

is created by

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...

throughout the stellar body, and the resulting flare activity generates a total

emission similar to that produced by the Sun.

Wolf 359

The flare star Wolf 359 is another near neighbor (2.39 ± 0.01 parsecs). This star, also known as Gliese 406 and CN Leo, is a

spectral class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

M6.5 that emits X-rays. It is a

flare star, and has a relatively high flare rate. The mean magnetic field has a strength of about (), but this varies significantly on time scales as short as six hours. By comparison, the magnetic field of the Sun averages (), although it can rise as high as () in active

sunspot Sunspots are phenomena on the Sun's photosphere that appear as temporary spots that are darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. S ...

regions.

Barnard's Star

Barnard's Star Barnard's Star is a red dwarf about six light-years from Earth in the constellation of Ophiuchus. It is the fourth-nearest-known individual star to the Sun after the three components of the Alpha Centauri system, and the closest star in t ...

is the fourth nearest star to the Sun. Given its age, at 7–12 billion years of age, Barnard's Star is considerably older than the Sun. It was long assumed to be quiescent in terms of stellar activity. However, in 1998, astronomers observed an intense stellar flare, showing that Barnard's Star is a flare star.

TVLM513-46546

TVLM 513-46546 is a very low mass M9 flare star, at the boundary between red dwarfs and

brown dwarfs Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the mos ...

. Data from

Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science ...

at radio wavelengths determined that the star flares every 7054 s with a precision of one one-hundredth of a second.

2MASS JJ18352154-3123385 A

The more massive member of the binary star 2MASS J1835, an M6.5 star, has strong X-ray activity indicative of a flare star, although it has never been directly observed to flare.

Record-setting flares

The most powerful stellar flare detected, as of December 2005, may have come from the active binary II Peg.Osten, Rachel; Drake, Steve; Tueller, Jack; Cameron, Brian
"Swift Observations of Stellar Flares"
Swift Team Meeting, 1 May 2007 Its observation by

Swift Swift or SWIFT most commonly refers to: * SWIFT, an international organization facilitating transactions between banks ** SWIFT code * Swift (programming language) * Swift (bird), a family of birds It may also refer to: Organizations * SWIFT, ...

suggested the presence of hard X-rays in the well-established Neupert effect as seen in

solar flares A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other sola ...

References

External links

UV Ceti and the flare stars, Autumn 2003 Variable Star Of The Season
prepared by Dr. Matthew Templeton, AAVSO (www.aavso.org)

- D. Montes, UCM. {{DEFAULTSORT:Flare Star Star types