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International research team puts universe’s fundamental constant to the test

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FCT Investigator Carlos Martins is a member of the research team that looked for changes in one of the fundamental constants of the universe – the fine structure constant. This constant’s value is used to characterise the behaviour of the electromagnetic force.

Using the three most powerful telescopes in the world (VLT, Keck  Subaru) the team looked for speed variations in the signature of light absorption (spectrum) of a quasar, the extremely bright nucleus of a distant, active galaxy that contains a supermassive black hole in its centre.

The light from the Quasar HS 1549 + 1919, 11.5 billion light-years away, travelled across three different galaxies, 10, 9 and 8 billion years ago, respectively. Some clues about the behaviour of the electromagnetic force were left as each galaxy absorbed the Quasar spectrum in its passage. These absorptions allowed scientists to measure the fine structure constant, α (or alpha).

Previous studies suggested that any variations of Alpha should be very small. Comparing measurements from the three telescopes helped minimise errors. All the data gathered points towards the same answer: if there have been variations in Alpha and, consequently, in the electromagnetic force, over the last 10 billion years, it has been less than a few parts per million. Michael Murphy, one of the co-authors of the study thinks that this is “the most accurate measurement to date”.

By presenting new and more precise measurements of the fine structure constant alpha and trying to unravel the true nature of dark energy, this study, published in the journal Monthly Notices of the Royal Astronomical Society, also contributes to the objectives of the FCT-supported project The Dark Side of the Universe, coordinated by Carlos Martins. The researcher considers that “spectrographs are pushed to the limit to perform these tests, so to improve them is fundamental to modern cosmology.