The Beta Pictoris moving group is a young

moving group In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as ...

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

s located relatively near

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. A moving group, in

astronomy Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...

, is a group of stars that share a common motion through space as well as a common origin. This moving group is named for

Beta Pictoris Beta Pictoris (abbreviated β Pictoris or β Pic) is the second brightest star in the constellation Pictor. It is located from the Solar System, and is 1.75 times as massive and 8.7 times as luminous as the Sun. The Beta Pictoris s ...

, a

A-type main sequence star An A-type main-sequence star (A) or A dwarf star is a main-sequence (hydrogen burning) star of spectral type A and luminosity class (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1.7 ...

with a

debris disk A debris disk (American English), or debris disc ( Commonwealth English), is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris ...

. The Beta Pictoris moving group is an important object for astronomical study as it is the closest youthful group of stars to the Earth. The star

is known to have a large disk of gas and dust, possibly a

protoplanetary disk A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may not be considered an accretion disk; while the two are sim ...

. There is also evidence of a young

gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet". However, in the 1990s, it became known that Uranu ...

planet around the star. A

free-floating planet A rogue planet, also termed a free-floating planet (FFP) or an isolated planetary-mass object (iPMO), is an interstellar object of planetary-mass object, planetary mass which is not gravitationally bound to any star or brown dwarf. Rogue plane ...

has also been found in the moving group, PSO J318.5-22. It has recently been estimated, , that more than a third of the single Sun-like stars in the group have planets with more than four times the mass of Jupiter, and virtually all of the single Sun-like stars, 99%, possess at least one gas giant in orbit around them. The age and distance of the group makes it a candidate for directly imaging

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first detect ...

Constituents

The Beta Pictoris moving group consists of 17 stellar systems, comprising a total of 28 individual component stars, including identified

brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...

s. The core of the group is located some 115

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s from Earth, and has an average estimated age of between 20 and 26 million years. The majority of the group is made up of cool, dim K and M

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

stars. Most are not visible to the naked eye. The members that are visible to the naked eye are: *

* Eta Telescopii * 51 Eridani * HD 203 * HD 146624 * HD 165189 * HD 172555 * Beta Trianguli Australis (potential member) The group covers a region of space for the most part visible only in the Southern Hemisphere, as shown in the map below.

Discovery

An early estimated age for the star Beta Pictoris at about 10 million years proved problematic due to the star's apparent isolation in space. According to current theory regarding

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is consi ...

, extremely young stars of this age should be located near other young stars that formed from the same region in space. It is not until significantly later that gravitational interactions with other stars causes stellar 'siblings' to disperse. In 1999 the situation was resolved by the discovery of a pair of dim

red dwarf A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...

stars that were found to have a similar velocity and age to β Pictoris, lending credence to the estimated age of the star. Further work published in 2001 identified a total of 17 stellar systems with a similar motion and age as the Beta Pictoris moving group, named for the primary member of the association.

Origin

The movements of the group were tracked to the positions they occupied 11.5 Myr ago, where they occupied a space 3 times smaller than their current distribution (24 pc, versus 72 pc today) situated in between two regions of the Scorpius-Centaurus OB star group, and it was suggested that they originated there when a supernova from either OB region of Scorpius-Centaurus OB would have been close enough to trigger stellar formation.

References

{{Reflist, refs= {{cite journal , title=On the age of the beta Pictoris moving group , last1=Mamajek , first1=Eric E. , last2=Bell , first2=Cameron P. M. , journal=Monthly Notices of the Royal Astronomical Society , volume=445 , issue=3 , pages=2169–2180 , year=2014 , arxiv=1409.2737 , bibcode=2014MNRAS.445.2169M , doi=10.1093/mnras/stu1894 , doi-access=free Moving groups

Constituents

Discovery

Origin

See also

References