News in Science

Dead star leaves astronomers in the dark

Mystery remains A team of astronomers have peered at a distant white dwarf star to confirm whether one of Nature's so-called constants varies changes throughout the cosmos.

The research published in the journal Physical Review Letters, suggests that despite the extreme gravity surrounding the star, it isn't enough to affect the strength of the electromagnetic force, one of the fundamental forces in the standard model of physics.

"Recent observations of quasars, hinted that the strength of electromagnetism could be different, in different parts of the universe, compared to its strength on Earth," says the study's lead author Dr Julian Berengut of the University of New South Wales.

Berengut and colleagues used the Keck telescope in Hawaii, and the Very Large Telescope in Chile, to study 300 quasars in different parts of the sky, up to 12 billion light years distant.

Quasars are extremely powerful jets of matter and energy thought to be generated by black holes in the centre of distant galaxies.

They were surprised to find the electromagnetic strength -- one of the great constants of physics -- seemed to be slightly weaker in one direction of the sky and stronger in the opposite direction.

"We're somewhere in the middle of this strange universe where electromagnetism seems to be changing from one side of the cosmos to the other," says Berengut. "We don't really know why that would be."

Turning to Hubble

To determine if strong gravitational fields effect the strength of electromagnetism, Berengut and colleagues used the Hubble Space Telescope to examine spectral lines emitted by ionised nickel and iron surrounding a distant white dwarf star called G191-B2B.

White dwarfs, which are stellar corpses of stars like the Sun, have 30,000 times more gravity than on Earth.

"The spectral lines act like fingerprints for atoms," says Berengut.

"We can compare the position of these lines relative to each other -- some might go to the right and some to the left. There's a particular signature associated with a change in electromagnetic strength, and that's what we're looking for."

Berengut and colleagues found the strength of electromagnetism was the same in the high-gravity environment of the white dwarf, as it was in the laboratory on Earth.

However, Berengut says the resolution of the results measured in the laboratory were significantly lower than that of the Hubble observations.

"What we don't know is if there are any changes below that level, we have some hints that there might be something going on, but the data is really not good enough to say for sure," says Berengut.

According to Berengut, the spectral signatures they're looking for, are deep in the ultraviolet part of the spectrum. The equipment needed to measure in this part of the spectrum is only available in a few laboratories.

"When new data from the laboratory becomes available, then we'll be able to get a much better reading of what the strength of the electromagnetism is, and if it changes," says Berengut.

Until then, the electromagnetic constant remains just that -- a constant.