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Wrap your mind around this: Neutron stars, the collapsed cores of once-large stars, are thought to be so dense that a teaspoon of one would weigh more than Mount Everest.

​Professor John Bally

These are the kind of amazing astrophysical features that help fuel the research interests of Professor John Bally of the Department of Astrophysical and Planetary Sciences, who studies the formation of stars and planets (including luminous, transient objects in space).

This week’s history-making news that a team of international scientists had discovered the first-ever evidence of the collision of two neutron stars—in the form of both gravity waves and electromagnetic waves—rocked well beyond the science world.

Bally was a co-author on two of the published studies, including one in Science magazine, describing the event. The new evidence builds on the first detection of gravitational waves in 2015, which scientists call the ripples in the fabric of space-time that are caused by some of the most violent and energetic processes in the universe.

“For the first time in human history we have detected both gravitational and electromagnetic waves from an astrophysical event,” Bally explains. “The merger confirmed the long-suspected notion that gravity and electromagnetic waves propagate through space at the speed of light. This foretells of a rich trove of future discoveries.”

Some other items about the new research you can talk about over the water cooler or the dinner table:

• While the merging neutron stars likely had masses greater than our sun, neither was wider than Washington D.C.
• In a neutron star collision, known as a “kilanova,” the two objects are thought to have been whirling around each other at more than a thousand times per second before merging.
• The studies indicate the collision of two neutron stars probably produced “heavy elements” like gold, silver and platinum that are now found, and prized, on Earth. Bally says the neutron star merger was the “perfect environment” to synthesize such rare earth elements and compounds. Scientists previously discovered that supernovas create some heavy elements, but not all.

Illustration of two neutron stars just before colliding (image courtesy of NASA)

Gravity-wave signals from the neutron star event encoded the distance of the object, allowing scientists to narrow their search to about a dozen galaxies. Less than two seconds after the gravity wave was detected, says Bally, the Fermi Gamma-Ray Space Telescope received a signal from the event, allowing scientists to narrow the search to a single galaxy. Within 12 hours a number of space- and Earth-based telescopes had located the neutron star smash-up.

“The real significance of this result is that it opens up a new window on our universe,” says Bally. “By detecting the violent cosmic processes producing both gravitational and electromagnetic waves, we will have a new way of probing the evolution of the universe over cosmic time and a means to study fundamental physical processes which may underlie the technologies and economies of the future.”

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