Sidereal clock

A physicist from Rio Grande do Sul shows how to make use of the variations in the brightness from pulsating white dwarf stars

The astrophysicist Kepler de Souza Oliveira Filho, from the Federal University of Rio Grande do Sul (UFRGS), was looking for something and found something else. First, he discovered a way of locating earth – like planets, rocky and suitable for the development of living organisms, as yet not found by current techniques: through pulses (variations in the amount of brightness) of the pulsating white dwarf stars, the final stage of stars such as our Sun, shortly before disappearing. “If the pulsation of the star varies, then there will probably be a planet close by”, he explains. “Today we can only identify planets so large that they have an influence on the stars’ orbit”.

Oliveira recently completed the equations that represent the state of evolution of two pulsating white dwarfs: the G117-B15A, situated some 150 light years from the Earth in the constellation named Leo Minor, and the R548, at 120 light years in the Cetus constellation. The points that represent the variation of the light emitted by these stars form parabolas – any other type of curve would represent the presence of terrestrial planets in their proximity.

Defying luck
Over a twenty-five-year period the UFRGS researcher accompanied the variation in the brightness of the two stars and carried out 82 million registrations of their luminosity, but did not find any planet “it would be an immense piece of luck”, he adds. Only in the Milky Way, out of a total of 100 billion stars, 100,000 are white dwarfs, just like the Sun.

Working on the limit of 300 light years, still in the Milky Way and relatively close to the Earth, the researcher for Rio Grande do Sul has data about another eighteen pulsating white dwarf stars and intends to examine the surrounding of one hundred others over the next five years.

As this type of star is on its death bed, the eventually close planets will also be dead, but it will be a notable advance if this proposal indicates that, shall we say, half of the dwarf stars still living, such as our Sun, have terrestrial like planets. His work, carried out up until now through an eleven-meter diameter telescope in Texas, in the United States, should take on new life through Soar – the astrophysics project that has Brazilian participation in Chile, and that will allow for a better understanding of the Southern Hemisphere stars.

Oliveira does not feel frustrated because he discovered extremely precious information: the pulsating white dwarfs are “the most perfect optical clock in the universe, much more precise that atomic clocks”, according to his own definition. The G117-B15A, with pulses at every 215 seconds, with seven digits after the point, as he has verified, could take as long as 100 million years – the time though which its temperature will fall by half – to get the rhythm of this pulsation late by second. This is a precision ten times better than the international standard of the atomic clocks based on decaying cesium, by which the slowing down by one second over a period of 10 million years is considered to be acceptable. “We could use the stars to calibrate the atomic clocks”, suggests the researcher.