Wayne State astronomers capture unprecedented view of neutron star environment

Breakthrough observation detailed in The Astrophysical Journal Letters

When Wayne State Astronomy Professor Renee Ludlam opened a new set of X-ray observations of a neutron star, it took only a moment for her to realize that a long-awaited discovery was sitting on her screen. Years of hints from older telescopes had never produced a definitive picture. This time was different.

"When I first reduced the data and saw the energy spectrum, I knew immediately that we were looking at something significant," Ludlam said. "Earlier X-ray missions hinted at structure in this region, but never with enough clarity to be certain. This research has given us the first high-fidelity view of emission from iron coming from gas circling around the neutron star. The high speed at which the gas is whipping around the neutron star, along with the star's strong gravity, shape what it looks like, and imprint effects of Einstein's relativity."

The data came from the X-ray Imaging and Spectroscopy Mission (XRISM), a joint mission led by Japan Aerospace Exploration Agency, NASA and the European Space Agency designed to study the high-energy universe with an unprecedented level of detail. Its Resolve microcalorimeter - essentially a high-tech thermometer - offers exceptional energy resolution over previous X-ray instruments, allowing scientists to dissect tiny variations in X-ray light that reveal conditions near compact objects such as neutron stars.

Ludlam's observation provides the clearest look to date at matter spiraling around Serpens X-1, a neutron star that strips material from its Sun-like companion. As this stolen matter heats to extreme temperatures, it emits X-rays, including iron emission lines that act as precise tracers of speed, gravity and geometry in the region closest to the neutron star.

The result, now published in the Astrophysical Journal Letters, helps map conditions extremely close to the neutron star and can provide new limits on its size.

The breakthrough is a milestone not only for the XRISM mission but also for Ludlam, who grew up in Dearborn, Mich., just a few miles from Wayne State's campus. She was one of the university's first graduates of the B.A. in astronomy program in 2015, but she didn't originally plan on a research career. She first encountered the program at FestiFall, WSU's annual kickoff to the academic year.

After that chance meeting with faculty in the Department of Physics and Astronomy, Ludlam jumped into a field she had previously considered a hobby.

She went on to earn a NASA Hubble Fellowship Program Einstein Fellowship at the California Institute of Technology, where she examined the question, "How does the universe work?" The fellowship supports promising postdoctoral scientists pursuing independent research across NASA Astrophysics.

With a research profile that could have taken her anywhere, Ludlam returned to Wayne State for a reason. "I wanted students here to have the same chance I had," she said.

Her homecoming created a full-circle moment. One of her collaborators on the XRISM project is Ed Cackett, now an associate dean in the College of Liberal Arts and Sciences and a world-renowned expert on black holes whose courses Ludlam once took as an undergraduate.

"This is the first study of its kind with these emission lines, which are so important for shaping what we see," Cackett said. "We are watching Einstein's theory of relativity at work in real time. It is remarkable."

In partnership with University of Michigan Professor Jon M. Miller and Javier A. García at NASA Goddard Space Flight Center, the project began with a proposal to NASA in April 2024. XRISM observed Serpens X-1 over four days in October 2024 and delivered the data weeks later.

Further analysis is underway, led by Wayne State graduate student Hayden Hall, who is incorporating data from additional missions to explore what the findings reveal about our understanding of the neutron star itself and the extreme phase of matter within.

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