Scientists have found a pulsar with two white dwarfs, which are all packed in a space smaller than the Earth’s orbit of the Sun.
These unusually close orbits allow the most precise measurements that have ever been able to have been obtained about gravity. This will hopefully allow scientists to resolve some difficulties with Einstein’s theories. And will let Scientists investigate theories of relativity, both generally and under extreme conditions, like never before.
The results will appear in the Nature journal and will be presented at the 223rd meeting of the American Astronomical Society which happens on the 23rd January.
The Pulsars emit lighthouse- like beams of radio waves that sweep through the stars as they spin on their axes.
Pulsars are formed after a supernova collapses to a burnt-out star to a dense, highly magnetised ball of neutrons. Using the Green Bank Telescope, the astronomers discovered a pulsar 4,200 light-years from Earth, spinning nearly 366 times per second.
Such rapidly-spinning pulsars are called millisecond pulsars – and they are used by astronomers as precision tools for studying gravitational effects and much more.
Subsequent observations of the pulsar showed the pulsar is in a close orbit with a white dwarf star, and that pair is in orbit with another, more-distant white dwarf.
The Green Bank telescope is a radio telescope based in West Virginia and is 100m wide. These statistics make this the world’s largest fully steerable radio telescope These types of systems are keenly studied because they allow competing theories of gravity and others to be tested.
However until now the only known triple system containing a millisecond pulsar was one with a planet as the outer part, unfortunately this causes only weak gravitational interactions .
By precisely timing the arrival of the pulses, the scientists are able to calculate the geometry of the system and the masses of the stars. The pulsar’s inner white-dwarf companion has an orbital period of less than two days, while the outer dwarf has a period of almost a year.
This particular system gives scientists the best opportunity yet to look out for the existence of the equivalence principle, described by Einstein. This states that the effect of gravity on a body doesn’t depend on the nature or internal structure of the body.
Famously, this was illustrated by Galileo’s dropping of two balls of different weights from the top of the Leaning Tower of Pisa, and the Commander of Apollo 15, Dave Scott’s dropping of a hammer and a feather while standing on the moon in 1971.
They found that rather than drifting from the ground, the feather plummeted and fell as fast as the hammer. Without air resistance, which slows the feather, both objects hit the lunar surface at the same time.
Finding any deviations would indicate the breakdown of Einstein’s theory and point Astronomers towards a new, correct theory of gravity.