The way space-time orbits a dead star confirms another prediction of Einstein’s general theory of relativity, a new study has found.
Einstein predicted a phenomenon called “frame of reference dragging,” also known as the lengze-tilling effect, that space-time would revolve around a massive object that was constantly rotating. It’s like soaking the earth in honey. As the earth spins, the honey around it spins.
Satellite experiments have detected reference frame dragging in the gravitational field of the earth’s rotation, but the effect is too weak to measure. The chances of seeing this phenomenon should be better around more massive objects with stronger gravitational fields, such as white dwarfs and neutron stars.
The scientists targeted PSR j1141-6545, a young pulsar about 1.27 times the mass of the sun. It is in the constellation of the fly, close to the famous constellation of the southern cross, and about 10,000 to 25,000 light years from earth. Pulsars are fast-spinning neutron stars that emit radio waves in the direction of their magnetic poles. (neutron stars are the remains of stars that die in violent explosions such as supernovas, and their gravitational pull is strong enough to squeeze protons and electrons together to form neutrons.)
Pulsar PSR j1141-6545 orbits a White Dwarf star about the mass of the sun. A White Dwarf is the core of an intermediate-sized star that has run out of fuel and died. Our sun will one day become a White Dwarf, as will more than 90 percent of the stars in our galaxy. The pulsar orbits a White Dwarf star in a very short orbit, traveling at speeds of up to 1 million kilometers per hour, making a full orbit in less than five hours. The orbit is very close to the White Dwarf, only slightly larger than the diameter of the sun at its maximum.
For nearly two decades, researchers have been using Australia’s parkes observatory and the rock-bottom radio telescope to measure the time it takes the pulsar to reach earth with an accuracy of less than 100 microseconds. They found a long-term shift in the way the pulsar and the White Dwarf orbit each other.
After ruling out other possible causes, the scientists concluded that the phenomenon was caused by the reference frame dragging effect: rapidly spinning white dwarfs were dragging on space-time, causing the direction of the pulsar’s orbit to gradually change. Based on the extent of the frame’s drag, the researchers calculated that the White Dwarf would rotate on its axis 30 times an hour.
Previous studies have shown that the White Dwarf formed earlier than the pulsar. The theoretical model predicts that the pulsar’s precursor dumped 20,000 earth-weight masses into the White Dwarf over a period of about 160 million years, accelerating its rotation, before the supernova that formed it.
“Pulsars are younger than white dwarfs in the PSR j1141-6545 system, which is quite rare.” The new study “confirms a 20-year-old hypothesis about how such binary systems form,” the researchers said.
The researchers say they used the reference frame drag to learn more about the spinning star that caused the phenomenon. In the future, they could use similar techniques to analyze binary neutron star systems and learn more about their internal composition. “We’ve been observing binary neutron star systems for more than 50 years, and we still don’t have a clue.” “The density of matter inside a neutron star is much higher than what can be achieved in the laboratory, so if we can use this technique to study a binary neutron star system, we will learn a lot of new physics,” the researchers said.