Newspaper article The Christian Science Monitor

Einstein's Theory of General Relativity Gets Most Extreme Test Yet

Newspaper article The Christian Science Monitor

Einstein's Theory of General Relativity Gets Most Extreme Test Yet

Article excerpt

The most massive neutron star known and its tightly orbiting companion, a wimp of a white-dwarf, have provided one of the most extreme tests yet of Einstein's theory of general relativity.

The theory has again passed with flying colors - for now.

Although the theory has cleared test after test over the past century, researchers keep trying to find its limits. They don't think it's wrong, just incomplete.

The other basic forces of nature - the strong force, which binds particles in an atom's nucleus, the weak force, which governs radioactive decay, and electromagnetism - have found explanations in quantum physics. Gravity is the only force that so far has resisted assimilation.

Many physicists are convinced that resistance is futile and that at some point gravity will yield to a quantum-physics explanation. But that breakdown may only become apparent under the most extreme conditions - conditions no human technology can establish.

So researchers turn to the cosmos for their extremes. And in the binary pair identified as PSR J0348+0432, they've found perhaps the most extreme conditions yet.


The pair is located some 7,000 light-years from Earth. The neutron star is all that remains of a star at least 10 times more massive than the sun that ended its luminous run in an explosion known as a supernova. Astronomers estimate that the neutron star is about 12 miles across. But it is so dense that a thimble full of the matter the explosion left behind would weigh about 1 billion tons.

It's white dwarf companion is the slowly cooling end state of a star like the sun.

White dwarfs are dense as well, typically packing roughly half of the sun's mass into an object slightly larger than Earth. This one, however is a lightweight, tipping the scales at about 17 percent of the sun's mass into an object roughly seven times larger than Earth.

Follow-up observations at radio and visible wavelengths revealed a duo that orbits its combined center of mass once every 2.46 hours. Considering the two objects are about a 500,000 miles apart, that's a mighty brisk pace.

"What we were looking for were changes in the orbital period," Dr. Lynch explains, referring to the time it takes for the two objects to orbit each other.

Those changes arise because the act of orbiting dissipates energy. That energy leaves in the form of gravity waves - ripples in space-time, the very fabric of the cosmos. These ripples travel through space almost as though some interstellar housekeeper was shaking out the sheets.

This loss of energy shortens the time it takes to complete an orbit, signaling that the two objects are slowing and inching closer to one another. Different theories of gravity offer up different predictions for the rate at which the orbits of objects as close and as massive as these decay. …

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