Pune: A team of three astronomers, Nissim Kanekar and Jayaram Chengalur from National Centre for Radio Astrophysics (NCRA-TIFR), Pune, and Tapasi Ghosh from Arecibo Observatory, USA, have shown that fundamental constants in physics don’t change with time.
For the research, the trio used the world’s largest telescope, the 300-metre-diameter Arecibo Telescope in Puerto Rico. The telescope was used to test whether two of the most fundamental constants in physics had the same value in the early Universe as they have today.
The constants are the ratio (mu) of the masses of two elementary particles, proton and electron, and the ‘fine structure constant’, alpha, which determines the strength of the electromagnetic force between charged particles. The detection of changes in either constant would require new physics beyond the standard model.
The team carried out one of the deepest ever observations with the help of the telescope, observing spectral lines from the hydroxyl (OH) molecule from a gas cloud near a quasar at a redshift of 0.25. These specific spectral lines were targeted because they have the remarkable property of being mirror images of one another, which greatly improves the reliability of the measurement.
This conjugate behaviour arises due to a combination of quantum mechanical selection rules and maser emission. “This is a beautiful case of quantum mechanical rules yielding observational effects in a distant galaxy and allowing us to probe fundamental physics,” said Kanekar, the first author of the paper on the new findings. It was published on February 8 in Physical Review Letters.
Kanekar said that the two OH line frequencies depend on the values of alpha and mu. If alpha and mu were different at the galaxy’s redshift (nearly 3 billion years in the past), the line frequencies will be slightly different from those measured in the laboratory and the two lines will not be observed to be exact mirror images of one another. The team found that the OH lines remain perfectly conjugate within the accuracy of the present data. They then used a combination of laboratory measurements done by other groups as well as their own earlier theoretical work to conclude that alpha and mu have not changed by more than a few parts in a million over the last 3 billion years.
“The use of the Arecibo Telescope was critical to achieve the high accuracy of the result,” said Ghosh. “Although the telescope is more than 50 years old, it is still the most sensitive radio telescope in the world as it has been updated from time to time.”
Chengalur said, “It is important to find such conjugate OH lines at even higher redshifts, corresponding to even earlier times, so that we can test for changes in alpha and mu over larger fractions of the age of the Universe.” The team plans to carry out searches for more distant OH systems with the new receivers of the upgraded Giant Metrewave Radio Telescope near Pune.