spaceSpace and Physics

Strength Of The Electromagnetic Force In Stars Found With Highest Precision Yet

Astronomers measured it in 17 Sun-like stars and got incredible precision.


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockNov 10 2022, 19:00 UTC
A series of rows going from deep red on the top to deep violet at the bottom, with some vertical dark lines.
The solar spectrum is full of absorption lines due to the chemicals in the Sun's atmosphere absorbing specific wavelenghts of sunlight. Image Credit: N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF

Among all the constants of nature, there is one that is severely underappreciated. It’s known as the fine structure constant and it underpins the strength of electromagnetic interactions. Its value is 1/137.03599913 and we don’t know why. Maybe, it is not really constant, a hypothesis that has been tested time and time again. The latest attempt is by using stars.

The fine structure constant underpins so much. If the number was different, stars might not burn the same and life might not evolve. A 4 percent variation would stop stars from making carbon. It is the reason why the sky is blue and why toast falls on the buttered side. But we don’t know where it comes from and, without that knowledge, if it truly stays constant.


Researchers have now studied the light spectrum of 17 solar twins, stars with atmospheric properties just like the Sun. Astronomers know how to study the chemical composition of a star by measuring absorption lines in its light. Different chemicals block some starlight at specific wavelengths, creating such lines. And those wavelengths depend on the fine structure constant. By picking stars like the Sun, it is possible to have a more precise measurement.

The team was able to estimate that the fine structure constant doesn’t change by more than 50 parts per billion in each star within 50 parsecs from Earth. The combined results tell us that the fine structure constant doesn’t change by more than 12 parts per billion.

“We’ve never tested electromagnetism outside our Earth so precisely before. It’s like testing whether the distance from Melbourne to Sydney changed by a few centimetres or so,” lead author Professor Michael Murphy from Swinburne University of Technology said in a statement. “If we’d seen electromagnetism change between stars, it would break the laws of nature as we currently understand them. We’d need completely new ideas to explain it.”


The defunct Arecibo telescope was previously used to test the changes of the constant over the last 3 billion years and it found that it had changed by no more than 1.3 parts per million. While focused on a smaller region, this work was 100 times more precise.

“Unfortunately, our new measurements didn’t break our favourite theory. But the stars we’ve studied are all relatively nearby, only up to 160 light years away. We’ve recently identified new solar twins much further away, about halfway to the centre of our Milky Way galaxy,” Professor Murphy added. “If we can observe these much more distant Suns with the largest optical telescopes, maybe we’ll find the keys to the Universe.”

The work was published in the journal Science.

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