Beta Pictoris
Beta Pictoris (abbreviated β Pictoris or β Pic) is the second brightest star in the constellation Pictor. It is located 63.4 light-years (19.4 pc) from the Solar System, and is 1.75 times as massive and 8.7 times as luminous as the Sun. The Beta Pictoris system is very young, only 20 to 26 million years old,[12] although it is already in the main sequence stage of its evolution.[8] Beta Pictoris is the title member of the Beta Pictoris moving group, an association of young stars which share the same motion through space and have the same age.[13]
The European Southern Observatory (ESO) has confirmed the presence of two planets, Beta Pictoris b,[14] and Beta Pictoris c,[15] through the use of direct imagery. Both planets are orbiting in the plane of the debris disk surrounding the star. Beta Pictoris c is currently the closest extrasolar planet to its star ever photographed: the observed separation is roughly the same as the distance between the asteroid belt and the Sun.[15]
Beta Pictoris shows an excess of infrared emission[16] compared to normal stars of its type, which is caused by large quantities of dust and gas (including carbon monoxide)[17][18] near the star. Detailed observations reveal a large disk of dust and gas orbiting the star, which was the first debris disk to be imaged around another star.[19] In addition to the presence of several planetesimal belts[20] and cometary activity,[21] there are indications that planets have formed within this disk and that the processes of planet formation may be ongoing.[22] Material from the Beta Pictoris debris disk is thought to be the dominant source of interstellar meteoroids in the Solar System.[23]
Location and visibility[edit]
Beta Pictoris is a star in the southern constellation of Pictor, the Easel, and is located to the west of the bright star Canopus.[24] It traditionally marked the sounding line of the ship Argo Navis, before the constellation was split.[25] The star has an apparent visual magnitude of 3.861,[1] so is visible to the naked eye under good conditions, though light pollution may result in stars dimmer than magnitude 3 being too dim to see. It is the second brightest in its constellation, exceeded only by Alpha Pictoris, which has an apparent magnitude of 3.30.[26]
The distance to Beta Pictoris and many other stars was measured by the Hipparcos satellite. This was done by measuring its trigonometric parallax: the slight displacement in its position observed as the Earth moves around the Sun. Beta Pictoris was found to exhibit a parallax of 51.87 milliarcseconds,[27] a value which was later revised to 51.44 milliarcseconds when the data was reanalyzed taking systematic errors more carefully into account.[6] The distance to Beta Pictoris is therefore 63.4 light years, with an uncertainty of 0.1 light years.[28][note 1]
The Hipparcos satellite also measured the proper motion of Beta Pictoris: it is traveling eastwards at a rate of 4.65 milliarcseconds per year, and northwards at a rate of 83.10 milliarcseconds per year.[6] Measurements of the Doppler shift of the star's spectrum reveals it is moving away from Earth at a rate of 20 km/s.[5] Several other stars share the same motion through space as Beta Pictoris and likely formed from the same gas cloud at roughly the same time: these comprise the Beta Pictoris moving group.[13]
Dust stream[edit]
In 2000, observations made with the Advanced Meteor Orbit Radar facility in New Zealand revealed the presence of a stream of particles coming from the direction of Beta Pictoris, which may be a dominant source of interstellar meteoroids in the Solar System.[23] The particles in the Beta Pictoris dust stream are relatively large, with radii exceeding 20 micrometers, and their velocities suggest that they must have left the Beta Pictoris system at roughly 25 km/s. These particles may have been ejected from the Beta Pictoris debris disk as a result of the migration of gas giant planets within the disk and may be an indication that the Beta Pictoris system is forming an Oort cloud.[70] Numerical modeling of dust ejection indicates radiation pressure may also be responsible and suggests that planets further than about 1 AU from the star cannot directly cause the dust stream.[71]