Students Tune Into a Cosmic Hum
An astrophysics major, rising senior Melanie Ficarra and her student team search the starry skies for “cosmic clocks,” part of an international consortium’s research project that this week reported evidence of gravitational waves that oscillate periodically from years to decades.
“My research involves identifying pulsars using data that has been collected using several large radio telescopes,” she says. “We follow certain criteria to determine if each candidate signal is a possible pulsar or not.”
Ficarra is among hundreds of students nationally and internationally who for the last decade have worked on pulsar and gravitational wave research, many of them with F&M Astrophysics Professor Fronefield Crawford, who manages NANOGrav Consortium’s NANOGrav Student Teams of Astrophysics Researchers (NANOStars) program.
Crawford is part of the team of astrophysicists from the United States and Canada who found evidence for periodically oscillating gravitational waves, according to a set of papers published this week in The Astrophysical Journal Letters.
“By detecting and characterizing these kinds of signals, we’re really opening up a new window into studying and understanding the objects that are producing those signals, how they evolve, and how they connect to the evolution of the universe as a whole,” Crawford says.
The team, using large radio telescopes directed toward a collection of cosmic clocks in the Milky Way galaxy, observed signals in 15 years of data acquired by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) Physics Frontiers Center (PFC), a collaboration of more than 190 scientists who use pulsars to search for gravitational waves.
“The basic idea is that we use a collection of radio pulsars in our galaxy that act as extremely precise clocks, and by monitoring these pulsars over time, we are sensitive to the presence of weak gravitational waves,” the Charles A. Dana Professor of Physics and Astronomy and director of F&M’s Grundy Observatory says.
While NANOGrav’s earlier results uncovered an enigmatic timing signal common to the pulsars they observed, it was too faint to reveal its origin. The 15-year data release demonstrates that the signal is consistent with slowly undulating gravitational waves passing through our galaxy.
“This is the first evidence for gravitational waves at very low frequencies,” says Vanderbilt University’s Stephen Taylor, who co-led the search and is the current chair of the collaboration.
Astronomers turned the Earth’s sector of the Milky Way galaxy into a huge gravitational-wave antenna by using pulsars. NANOGrav’s 15-year effort collected data from 68 pulsars to form a type of detector called a pulsar timing array.
A pulsar is the ultradense remnant of a massive star's core following its demise in a supernova explosion. Pulsars spin rapidly, sweeping beams of radio waves through space so that they appear to “pulse” when seen from Earth. The fastest, called millisecond pulsars, spin hundreds of times a second. Their stable pulses make them useful as precise cosmic timepieces.
“Our approach is a bit unusual: In a typical scientific experiment, you would build a detector to detect a signal, and then you would run an experiment by collecting some data and making some measurements,” Crawford says. “Here, instead of building a physical detector, we’re finding new pulsars in our galaxy that act as our gravitational wave detector.
With more than 15 years of observations with the Arecibo Observatory in Puerto Rico, the Green Bank Telescope in West Virginia, and the Very Large Array in New Mexico, NANOGrav has gradually expanded the number of pulsars they observe.
"NANOStars was my first research opportunity at F&M, and it was a great program to start astronomy research.”– Melanie Ficarra
For the F&M students’ research in determining pulsars, Ficarra says her team used a program that a fellow team leader, rising senior Wenky Xia, “wrote to make this process more efficient.”
“We meet as a group every week to discuss our progress and attend teleconferences every few weeks to connect with other colleges and universities working with NANOGrav,” says Ficarra, who plans to pursue a doctorate. “NANOStars was my first research opportunity at F&M, and it was a great program to start astronomy research.”
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