Illuminating the origin of neutron stars and black holes

Lilia Ferrario is studying neutron stars and black holes. She does not use a telescope, however, but mathematics, the laws of physics and a computer.

Ferrario, is a member of the astronomy and astrophysics group within the Australian National University's Mathematical Sciences Institute. She is among a growing number of mathematicians world wide working on the theoretical modelling of astrophysical systems.

She is modelling stars in their death throes. Her exploration of the virtual cosmos promises to answer big questions about the evolution of the most violent objects in the universe.

"What scientists get when they spend a night at a telescope is a vast amount of data, but you have to understand what the data are telling you - to understand what kind of engine is behind the observations," she says.

Her work centres on stars that have burnt up all their fuel in nuclear fusion reactions. The massive dying stars, or supernovae, explode and collapse under their own mass to form super-dense objects. Lighter stars form white dwarfs, while heavier ones are thought to be the progenitors of neutron stars - the source of high intensity x-rays and gamma rays - and black holes.

Scientists have long argued about the origin of these exotic objects, with the debate centring on the mass of the progenitor stars. Ferrario is developing mathematical "population synthesis" models testing them against empirical data. She is focusing on magnetars - neutron stars with incomprehensibly high magnetic fields.

She assigns to candidate progenitor stars a magnetic field and mass and "evolves" them to see which ones wind up as magnetars. She also predicts how many magnetars are out there, comparing the predictions with the observations.

"It appears that some of their progenitor stars were extremely massive, more than 40 times the mass of our sun," she says. "They exploded and the surviving remnant core is a rapidly spinning, highly magnetic neutron star.

Previously, it was thought that stars that big would form black holes. "observations are at odds with all theories on stellar evolution," she says of the results. "There are few stars as massive as that. The galaxy is mainly populated by low mass stars."

Ferrario wants to trace the origin of the super strong magnetic fields to find out when in the star's evolution they originated.

She says she was attracted to the ANU by its strength in computational mathematics. "I hope I will be able to shed some light on where neutron stars and black holes come from."