Astronomers studying an absolutely enormous neutron star and its white dwarf companion have shown that Einstein’s calculations still work even under the most extreme gravitational conditions.
And indeed, extreme is the word to use when describing this binary system. Located 7,000 light years away, the neutron star has twice the mass of our sun — but it’s only 12 miles (20 km) across. This means that its surface gravity is 300 billion times stronger than Earth’s, and that each cubic centimeter of the neutron star contains more than a billion tons of matter.
What’s more, this way heavy neutron star — the remnant of a mass accretion supernova explosion — spins around 25 times every second, and a lingering white dwarf star rapidly orbits around it once every 2.46 hours.
The neutron star is a pulsar, called PSR J0348+0432, that gives off radio waves that can be picked up here on Earth. Specifically, astronomers used the Aricebo and Effelsberg telescopes to make their radio-timing observations.
Now, because this binary system offers such unprecedented data (it’s only the second neutron star discovered with this kind of mass), the astronomers were curious to see if their real-world measurements would deviate from the math produced by Einstein’s equations; they calculated the amount of gravitational radiation emitted to see if the theory could accurately predict the rate of orbital decay.
They independently measured the rate of decay at 8 millionths of a second per year (yes, that’s the degree of preciseness offered by the pulsar’s emissions).
The figures matched.
"We thought this system might be extreme enough to show a breakdown in General Relativity, but instead, Einstein's predictions held up quite well," said Paulo Freire of Germany's Max Planck Institute for Radioastronomy in a statement.
Interestingly, the astronomers predict that the system will eventually change into an ultracompact X-ray binary, possibly leading to a pulsar-planet system — or even the formation of a black hole.
Check out the entire study in Science: “A Massive Pulsar in a Compact Relativistic Binary.”