1984

Circumstellar Disks

Bernard Lyot (1897–1952)

The prevailing theory for the formation of our solar system is that an enormous cloud of gas and dust—perhaps the remnants from the supernova explosion of a previous-generation star—slowly began to gravitationally contract, spin, and flatten into a disk of condensing material. More than 99 percent of the mass in this Solar Nebula disk went into the Sun. Most of the rest formed Jupiter, and we all live on a tiny speck of the leftovers. If this model is correct, then it should also have occurred around other stars, especially around Sun-like stars, which are very common in the Milky Way galaxy. Astronomers looked for evidence of disks, rings, or halos of dust around stars, but the search was effectively impossible because direct starlight is a million to a billion times brighter than the light reflected from any disks or planets that might orbit them.

A critical breakthrough was the use of a special telescopic attachment called a coronagraph, invented by the French astronomer Bernard Lyot in 1930 to help block direct sunlight so that astronomers could observe the Sun’s upper atmosphere, or corona. Using a smaller version of the device, astronomers could block out the direct light from a star and detect the faint light from objects close to the star.

In 1983 the joint NASA, Dutch, and British space telescope called the Infrared Astronomical Satellite (IRAS) conducted the first all-sky survey of infrared heat energy emitted by cosmic objects. IRAS data revealed an unusual excess of low-temperature infrared heat energy around the young star Beta Pictoris, speculated to be from dusty or rocky material in orbit around the star. The speculation was confirmed in 1984, when astronomers observing with a specially designed Lyot-style coronagraph from the 8.2-foot (2.5-meter) telescope at Las Campanas Observatory in Chile observed a spectacular dusty and rocky circumstellar disk extending some 400 astronomical units (AU) from the center of the star—evidence of a solar nebula around another star.

The Beta Pictoris disk is now one of many known circumstellar disks believed to be young solar systems caught in the act of formation. In 2008 astronomers imaged even closer to Beta Pic and discovered a giant planet about 8 times the mass of Jupiter orbiting just 8 AU from the star—one of the first directly imaged extrasolar planets.

A composite near-infrared image of the dusty disk around Beta Pictoris, obtained from the 12-foot (3.6-meter) telescope at the European Southern Observatory (ESO), superimposed on an ESO Very Large Telescope view that reveals a large planetary companion (blue dot) orbiting close in, near the (blocked-out) star.