While astronomers around the world discussed whether Pluto should be demoted from planet to dwarf planet, the Southern African Large Telescope (Salt) quietly released its first public research results, giving new insight into a pair of stars closely orbiting one another.
The new Salt results are for a "polar" binary star system, which contains a compact star called a white dwarf.
The powerful gravitational field of a compact star commonly pulls in gas from a companion star.
The polar that Salt has studied takes 1½ hours to complete an orbit (compared with a month for the earth and moon, and a year for the earth and sun). The two stars are so close you would see them as only one in a telescope. One of the stars is an ordinary star like the sun, but cooler, redder and about a third of the sun's mass and radius. Its white dwarf companion is hundreds of thousands of times as dense as the earth - a chunk of white dwarf as large as a pair of dice would weigh as much as two small trucks.
This gives the white dwarf an intense gravitational field which sucks in material from the larger star. But it is the white dwarf's huge magnetic field (30m times as strong as the earth's) that forces the gas from the cool star towards the white dwarf's magnetic poles. The picture alongside is an artist's impression of what this binary system might look like: the cool, red star is in the background with the stream of gas being sucked off by gravity shown in white, finding its way to the white dwarf along a path shaped by magnetic forces.
This research was made possible by Salt's ability - rare among large telescopes - to take "snapshots" of stars in quick succession so that astronomers can study the rapidly changing properties of compact stars, especially as they pull in gas from their companions. The measurements are better than anything that has been obtained before, and Salt's advantages over other large telescopes for this type of research should allow its astronomers to lead in probing the mysteries of these "cannibal stars".
