Joel Weisberg, the Herman and Gertrude Mosier Stark Professor of Physics and Astronomy and the Natural Sciences, is part of a team that calculated the mass of a neutron star and its binary companion, using Einstein’s General Theory of Relativity, and recently published the findings in The Astrophysical Journal. Weisberg was included in the team due to his expertise in binary pulsars, which he has intensively studied for more than 35 years.

The team measured the space-time warp caused by the grav- ity of the pair of stars and determined their masses — just before the pulsar member disappeared. “These two stars each weigh more than the Sun, but are still over 100 times closer together than the Earth is to the Sun,” notes co-author Ingrid Stairs, professor of physics and astronomy at The University of British Columbia, Canada.

“Our result is important because weighing stars while they freely float through space is exceedingly difficult,” said Joeri van Leeuwen, an astrophysicist at ASTRON, The Netherlands Institute for Radio Astronomy, and University of Amsterdam, The Netherlands, who led the study. “That is a problem because such mass measurements are required for precisely understanding gravity, the force that is intimately linked to the behavior of space and time on all scales in our Universe.”

The resulting extreme gravity causes many remarkable effects, said Stairs.

The pulsar was discovered in 2004 with the Arecibo Observatory, the world’s most sensitive radio telescope due to its large, 305-meter dish.

Weisberg has taken numerous Carleton students to observe pulsars with this telescope, including Yuping Huang ’17 and Carolyn Raithel ’15 in December.

From that moment on, the team monitored the pulsar almost daily with the five largest radio telescopes on Earth.

For more than five years the campaign kept exact score of all rotations of the pulsar — an astounding one billion in total.

Each few-minute chunk of these data enabled the team to measure the pulse times of arrival with a precision of less than 50 millionths of a second, until the pulsar started to fade away due to geodetic precession.