2011 Nobel Prize in Physics


Yesterday morning, the Nobel Prize in Physics 2011 was awarded, "For the discovery of the accelerating expansion of the Universe through observations of distant supernovae," with one half to Saul Perlmutter (Lawrence Berkeley National Lab) and the other half jointly to Brian P. Schmidt (Australian National University),and Adam G. Riess (Johns Hopkins Univ & Space Telescope Science Institute). 

The Nobel Prize website says,

"The research teams [of Perlmutter and Schmidt] raced to map the Universe by locating the most distant supernovae. More sophisticated telescopes on the ground and in space, as well as more powerful computers and new digital imaging sensors (CCD, Nobel Prize in Physics in 2009), opened the possibility in the 1990s to add more pieces to the cosmological puzzle.

"The teams used a particular kind of supernova, called type Ia supernova. It is an explosion of an old compact star that is as heavy as the Sun but as small as the Earth. A single such supernova can emit as much light as a whole galaxy. All in all, the two research teams found over 50 distant supernovae whose light was weaker than expected - this was a sign that the expansion of the Universe was accelerating. The potential pitfalls had been numerous, and the scientists found reassurance in the fact that both groups had reached the same astonishing conclusion."

TRIUMF and other labs pursuing nuclear astrophysics are playing key roles in understanding the nuclear physics of SN Ia so that eventually the yardstick technology can be fully understood.   How does this work?  TRIUMF studies the detailed nuclear reactions that occur in Type 1a supernovae; this in turn allows observers to make more precise comparisons between what they expect to see in the night sky and what is actually observed.

Type Ia supernovae have recently been proposed as a major source of so-called "p-nuclei". These are nuclei of around 35 different kinds between mass numbers 74 and 196 that are slightly neutron-deficient, but stable, and are separated from their more neutron-rich stable neighbours by one or two radioactive isotopes.  This means they are unlikely to be able to be produced in a standard mechanism of stellar nucleosynthesis. However in SN1a they can be produced in something called the "gamma process", where they are created via the disintegration of slightly more neutron-rich nuclei when bombarded with high energy photons (gamma rays).

In order to understand nucleosynthesis of these nuclei, the nuclear reactions which create and destroy them have to be measured in the laboratory.  Theoretical models are so far insufficient to calculate the reaction rates with good precision. In particular, proton and alpha fusion reactions on these nuclei are important. The DRAGON facility at TRIUMF was built to study these proton and alpha fusion reactions with nuclei of lower masses than the p-nuclei, but recently it was determined that the DRAGON facility can perform well at these higher masses to do measurements for the gamma process as well. A program in this area will kick off in 2012 with a measurement of alpha capture on selenium-76. It is hoped the data from these measurements will help elucidate astrophysical simulations of SNIa, making them ever closer to the observations, and allowing us to have deep insight into the working of these objects. 

Our highest praise and congratulations go to Professors Perlmutter, Riess, and Schmidt!  We learn more about ourselves and the universe in which we live through pioneering work such as theirs. 

--by T.I. Meyer, Head of Strategic Planning & Communication