Missing link uncovered in search for recycling on a cosmic scale

Researchers observe a dying pulsar reusing matter to revive itself

By Amy Minsky, Vancouver Sun – May 22, 2009

The green trend has, literally, reached cosmic proportions.

Researchers from McGill University and the University of British Columbia were among the first in the world to witness what they are calling a cosmic act of recycling.

A dying star was found to be using materials torn from a neighbouring star to increase its own speed and brightness.

PhD student Anne Archibald and her supervisor, McGill professor Victoria Kaspi, made the discovery while an international team of astrophysicists performed a survey of the sky. They were observing a system with one dying pulsar—a remnant from a stellar explosion—that was “gobbling up” material from a nearby companion star.

When Archibald and Kaspi’s team recently examined the system, they found the dying pulsar was spinning significantly faster than in 2000, when the transfer of materials was first observed by an independent research group.

Pulsars are highly magnetized neutron stars that spin moderately fast, but slow down as they age over a few thousand years.

“Pulsars are born spinning with a rotational speed of about 30 milliseconds,” Archibald said. “As they age, they slow down to a second or more, then eventually disappear.”

The pulsar Archibald and Kaspi observed was very old, yet spinning very quickly, with its rotational speed back into the milliseconds range.

“What they saw [in 2000] looked like it was in the middle of the recycling process,” Archibald said.

Based on those observations, Archibald said her team was able to confirm that the transferred materials had been recycled, and used to revive the pulsar by enabling it to increase its rotational speed.

Ingrid Stairs, an associate professor from UBC who contributes to this research, compared the process of the pulsar speeding up to that of a top.

“Before the process starts, the neutron star is spinning very slowly,” she said. “During recycling, matter that swirls onto it gives it a bit of a push and makes it spin faster, like a person’s fingers making a top spin faster.”

“This is very exciting,” said Marten Van Kerkwijk, a professor of astronomy and astrophysics at the University of Toronto. “We theorized that this was happening, and previous claims had been made about recycling, but they were always somewhat unbelievable. Now this is the real thing.”

In the past, astrophysicists had observed objects that appeared to be the product of recycling. But before Archibald’s discovery, Van Kerkwijk said, the recycling theory could not be confirmed.

Her team’s discovery offers an answer to the missing link in a pulsar’s transformation from an apparently dying star to a revived, spinning and bright pulsar, Archibald said.

Van Kerkwijk said the system will provide a “perfect example” for astrophysicists to understand the process by acting as a laboratory for studying the transfer of matter from one star to another, then the dying star’s renewal and rebirth.