G191-B2B, a stellar test on a constant of nature
Un gruppo di fisici della University of New South Wales (UNSW) hanno studiato una nana bianca distante dove la gravità diventa oltre 30.000 volte maggiore rispetto alla superficie terrestre per verificare una teoria controversa sulla variabilità, o meno, di una delle costanti della natura.
“This idea that the laws of physics are different in different places in the cosmos is a huge claim, and needs to be backed up with solid evidence”, he says. “A white dwarf star was chosen for our study because it has been predicted that exotic, scalar energy fields could significant alter alpha in places where gravity is very strong. Scalar fields are forms of energy that often appear in theories of physics that seek to combine the Standard Model of particle physics with Einstein’s general theory of relativity. By measuring the value of alpha near the white dwarf and comparing it with its value here and now in the laboratory we can indirectly probe whether these alpha-changing scalar fields actually exist”. White dwarfs are very dense stars near the ends of their lives. The researchers studied the light absorbed by nickel and iron ions in the atmosphere of a white dwarf called G191-B2B. The ions are kept above the surface by the star’s strong radiation, despite the pull of its extremely strong gravitational field. “This absorption spectrum allows us to determine the value of alpha with high accuracy. We found that any difference between the value of alpha in the strong gravitational field of the white dwarf and its value on Earth must be smaller than one part in ten thousand”, Berengut says. “This means any scalar fields present in the star’s atmosphere must only weakly affect the electromagnetic force”. Berengut said that more precise measurements of the iron and nickel ions on earth are needed to complement the high-precision astronomical data. “Then we should be able to measure any change in alpha down to one part per million. That would help determine whether alpha is a true constant of Nature, or not”.
UNSW: White dwarf star throws light on constant of Nature Physical Review Letters: Fundamental Constant Doesn’t Budge in High Gravity arXiv: Limits on variations of the fine-structure constant with gravitational potential from white-dwarf spectra