Looking to the Stars: NASA Postdoctoral Fellow Gabriel Grell Explores the Universe One X-ray at a Time

Center: Goddard Space Flight Center

As a high school student growing up near Baltimore, Gabriel Grell knew two things about himself: he loved math and science, and he couldn’t stop asking questions about the universe.

Those questions — about black holes, distant galaxies, dark matter and the mysteries that still elude modern science — set him on a path led to NASA’s Goddard Space Flight Center, where he is a NASA Postdoctoral Program (NPP) Fellow. The NASA NPP Fellowship is administered by ORAU.

Today, Grell spends his days studying some of the most energetic and extreme objects in the universe. His research in X-ray astrophysics helps scientists better understand how stars evolve, how galaxies form and what happens in the violent environments surrounding black holes and supernovae.

“The sheer unknown in the field is what really drew me in,” Grell said. “We know so little about what’s going on in the universe and the underlying physics that explains it. Questions like, ‘Is there extraterrestrial life?’ ‘What is dark matter?’ ‘How were the earliest galaxies formed?’ Those are the kinds of questions that captured my imagination.”

A journey sparked by opportunity

Grell’s interest in astronomy became more than a hobby during high school when he earned a summer internship at the Space Telescope Science Institute in Baltimore.

“That was really the match that ignited my interest in the field,” he said.

He went on to earn bachelor’s degrees in astrophysics and physics from Harvard University before pursuing a doctorate at the University of Maryland, College Park. Through the Center for Research and Exploration in Space Science and Technology (CRESST II) cooperative program, he conducted his dissertation research alongside scientists at NASA Goddard’s X-ray Astrophysics Laboratory.

After completing his doctoral degree, Grell transitioned seamlessly into NASA’s Postdoctoral Program, allowing him to continue collaborating with many of the same researchers who helped shape his scientific career.

“It really is the best of both worlds,” he said. “I’m getting to do my dream job while also staying close to my family.”

Seeing the invisible

Although most people associate X-rays with medical imaging, Grell uses them to investigate some of the universe’s most powerful phenomena.

Massive stars, exploding supernovae, black holes and distant galaxies emit enormous amounts of X-ray radiation. Orbiting observatories collect those X-rays as photons, providing scientists with valuable information about objects that are often billions of light years away.

Grell analyzes the spectral signatures contained in those observations to determine the chemical composition and physical properties of celestial objects.

“The better we can improve our models and our measurements, the better we can understand exactly what we’re seeing in space,” he said.

His work combines sophisticated theoretical models with carefully controlled laboratory experiments. One of the team’s key tools is an electron beam ion trap, which replicates plasma states; plasma is the superheated state of matter found in stars.

“We’re able to replicate what’s happening in space under controlled laboratory conditions,” Grell explained. “As my advisor likes to say, we’re harnessing the power of the stars to understand them better.”

From astrophysics to everyday life

While Grell’s research focuses on distant corners of the universe, its impact reaches much closer to home.

The same plasma physics that helps researchers interpret cosmic X-rays also contributes to advances in nuclear fusion, medical imaging and national defense technologies.

“The field of plasma physics has a lot of real-world applications,” Grell said. “Nuclear fusion has the potential to be world changing. It also contributes to X-ray imaging and laser systems for defense. Improving our understanding of plasma benefits astrophysics, but it also has applications across many different fields.”

History has shown that discoveries driven by curiosity often produce unexpected benefits.

“The MRI was originally developed from research into the magnetic properties of atomic nuclei,” Grell noted. “Now it’s one of the most important medical instruments ever created. You never know where fundamental science will lead.”

Growing into independence

For Grell, the NASA Postdoctoral Program represents a significant milestone in his professional development.

As a postdoctoral fellow, he’s beginning to move beyond answering established research questions and toward defining his own.

“It’s probably the greatest level of independence I’ve had so far,” he said. “As you progress from undergraduate researcher to graduate student to postdoc, you gradually have your hand held less. Now I’m starting to think about my own research questions.”

That independence comes with both excitement and uncertainty.

“It’s exciting, but there’s definitely a little nervousness,” he admitted. “Fortunately, I’m still working with many of the mentors who helped me grow during graduate school, so I have that support while taking on more responsibility.”

The importance of mentorship

Throughout his academic career, Grell credits mentors with helping him navigate both scientific challenges and personal growth.

“They cared more about my growth as a scientist and as a person,” he said. “Having advisors who genuinely cared about my well-being made an enormous difference.”

Those experiences have shaped the advice he now gives students considering careers in STEM.

His first recommendation is to get involved in research as early as possible.

“Reach out to professors whose work interests you,” he said. “Send an email. Ask questions. Most faculty members are excited to work with motivated undergraduate students.”

His second recommendation is equally important: choose mentors carefully.

“Find someone who’s living the path you hope to follow,” Grell said. “You want someone who’s invested in helping you grow—not someone who’s simply looking for another person to do the work.”

Looking toward the future

Although still early in his postdoctoral career, Grell knows he wants to remain in X-ray astrophysics.

Whether that future keeps him at NASA Goddard or takes him to research institutions such as Germany’s Max Planck Institute for Nuclear Physics or Japan’s Institute of Space and Astronautical Science, his mission remains the same: advancing humanity’s understanding of the universe.

He also encourages graduating doctoral students to consider NASA’s Postdoctoral Program.

“The opportunities are tremendous,” he said. “Across NASA centers, there are so many different research areas and outstanding scientists to work with. The breadth of opportunities and the wealth of expertise make it an incredible place to build a career.”

For Grell, every new observation offers another opportunity to answer questions that have fascinated him since childhood—and perhaps uncover entirely new ones.

After all, the universe still holds countless mysteries waiting to be explored.