Supernova Ph.D. Student Selected for NASA Pathways

UMD astronomy student Isiah Holt studies the composition of neutron stars

Working at NASA has always been a dream for University of Maryland astronomy Ph.D. student Isiah Holt. He was thrilled to see his dream become a reality in January 2022 when he was selected for the Pathways internship program at NASA’s Goddard Space Flight Center, which offers a direct pipeline to full-time employment at NASA. 

“I didn’t expect my dream to come this fast,” Holt said. 

When he received an email from NASA Goddard and spotted the word “congratulations,” Holt immediately leaped from his bed and ran downstairs to tell his mom he was awarded a NASA Pathways internship—before he even read the email.  

“My initial reaction was, ‘Oh my goodness, did I just make it?’” Holt recalled. “All this time, I’ve been talking about NASA and how I want to work there. I start June 6 of this year, and I am prepared to put in the work and get a civil servant position after I graduate.” 

Narrowing in on Neutron Stars

When it came time to pick a major for undergrad, Holt thought back to the hours he’d spent as a kid watching the iconic 1980 TV series, “Cosmos.” His fascination with space held fast through middle and high school and only intensified at Penn State where he studied astronomy and astrophysics—and discovered a passion for neutron stars. 

“As soon as I got to Penn State, I really wanted to dig into the research,” Holt said. “I joined the Pulsar Search Collaboratory, which was a bunch of students who were interested in pulsars and how to detect them. That was my first time really studying neutron stars.”

Neutron stars are the collapsed cores of formerly massive stars that have been crushed to an extreme density by supernova explosions. While a neutron star isn’t as dense as a black hole, it is denser than any other known type of star.

“To give you an idea of just how dense they are,” Holt explained, “if you took every human on Earth and somehow fit them into one teaspoon—that’s about how dense neutron star core matter can be.”

Though Holt moved on from the Pulsar Search Collaboratory to conduct research on several different astrophysical subjects—including exoplanets, active galactic nuclei and fast radio bursts—neutron stars remained his top interest. 

Diving into Research

UMD’s proximity to and relationship with NASA Goddard were significant draws for Holt when he applied to graduate programs.  

“On top of the potential to work at NASA Goddard, I just loved the friendly vibe I got from my cohort and some of the professors when I toured at UMD,” Holt said. “I really do feel like I made the best choice in picking this program.”

When it came to selecting a research project, Holt knew he wanted to be on a NASA mission exploring neutron stars—which is why he pursued NASA Goddard’s Neutron star Interior Composition Explorer (NICER), an X-ray telescope on the International Space Station that provides high-precision measurements of neutron stars. After digging through campus resources, Holt found that UMD Astronomy Professor Cole Miller leads a team on the NICER mission—and Miller was happy for Holt to come aboard. 

“Isiah has a wonderful combination of enthusiasm, organization and a desire to learn,” said Miller, who is now Holt’s advisor. “To use a sports term, he is tremendously coachable.”

Holt’s role on the NICER mission is to identify systematic errors and determine whether the researchers’ models can get a statistically good fit to the data, even in cases of bias. Bias refers to the value of a neutron star’s radius being a certain number of standard deviations away from the expected value. In other words, if the fit to the data is statistically good, but the radius is very far off from the expected value, Holt will know the result is biased. 

“If we do find an instance of bias, we will think long and hard about why the radius is biased and proceed with caution in our modeling and data analysis. However, if we do not come across an instance of bias, then we can begin to trust radius measurements made by NICER,” Holt said. “Once we get reliable radius and mass values, then we can talk to the nuclear physicists to compare numbers and see if we can determine the matter inside the core. But my project comes down to ensuring that reliability.”

Ultimately, the team knows their models for neutron star measurements cannot be completely correct. By fitting incorrect models to synthetic data generated using the correct model, the team hopes to “explore the consequences of our guaranteed errors in a controlled environment and get a much better sense of whether we can trust our results,” Miller said.

“When we fit the correct model to the data generated by the correct model, the radius obviously comes out to be the expected radius value,” Holt explained. “That’s why we want to know what happens to the radius measurement when we fit the wrong model to the data generated using the correct model. Does the radius veer away from what we expect, or does it stay around the expected value? What is the quality of the statistical fit? These are the questions we’re asking ourselves to see if our model is reliable.” 

Giving Back

Starting in June, Holt will continue his NICER research under the umbrella of the Pathways program. The job security and financial assistance provided by the Pathways program will give him the freedom and resources to pay his academic success forward to others.  

“When I was an undergrad, I was given a fellowship that covered my tuition for four years, which was huge for me. I was also connected with a cohort of scholars from underrepresented backgrounds, where I was able to really find a sense of community,” Holt said. “Because of that, I feel called to do something like that for other minorities who want to be in STEM but can’t because they’re worried about financial stuff.” 

In addition to giving back financially, Holt also plans to share his time by volunteering with NASA’s outreach programs.  

“Doing outreach fixes my urge to communicate science to people,” Holt said. “I see outreach as teaching science in a purely fun way, with demos and whatever props I come up with. I am also really interested in plugging into mentorship opportunities at NASA, as both mentor and mentee.”

Now that Holt is living his dream, he plans to take his neutron star research as far as he can at NASA, starting with the Pathways internship.

“This whole trip from watching ‘Cosmos’ as a kid to now has been something else,” Holt said. “There are so many domino pieces that I’ve set up, taken out, set up again, and now it’s all falling into place. I’m so grateful to my family, friends and colleagues who have helped me get here. And I’m excited to get started at NASA—making those connections, possibly becoming a mentor to somebody, doing outreach and continuing my research.”


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