New research confirms the deaths of stellar giants are "lopsided" events in which the stars' cores are thrown in the opposite direction.
The recent observations backed up past prediction made by a supercomputer, the California Institute of Technology reported. A research team looked at remnant of supernova (SN) 1987A using NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) to detect the unique energy signature of titanium-44. This radioactive version of titanium is believed to be released during the early stages of a star's death.
"Titanium-44 is unstable. When it decays and turns into calcium, it emits gamma rays at a specific energy, which NuSTAR can detect," said Fiona Harrison, the Benjamin M. Rosen Professor of Physics at Caltech, and NuSTAR's principal investigator.
The team measured direction-dependent frequency changes (Doppler shifts) of energy from titanium-44, and determined material was moving away from the telescopes. This is the best evidence to date that the mechanism that triggers Type II supernovae is lopsided; these stars change shape from a sphere into a "wobbly mass" just before exploding.
"If you make everything just spherical, the core doesn't explode. It turns out you need asymmetries to make the star explode," Harrison said.
The change in shape is believed to be triggered by turbulence that is caused by neutrinos absorbed in the star's doomed core.
"This turbulence helps push out a powerful shock wave and launch the explosion," said Christian Ott, a professor of theoretical physics at Caltech who was not involved in the NuSTAR observations.
These new insights into the asymmetry of Type II supernovae could help solve the long-standing mystery of why some supernovae collapse into neutron stars and others black holes. The researchers suggested it could be determined by the high degree of symmetry seen in some supernovae that causes the star to explode in one direction while the rest collapses in another.
"In this way, an explosion could happen, but eventually leave behind a black hole and not a neutron star," Ott said.
The findings were published in a recent edition of the journal Science.
