Lee Hartmann Inducted into the National Academy of Sciences
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Lee Hartmann has been inducted into the National Academy of Sciences (NAS), one of the highest honors a scientist can receive. Established in 1863, the NAS recognizes individuals who have made outstanding contributions to scientific research, and membership is considered a mark of excellence in the scientific community. Renowned for his remarkable contributions to astronomy, most notably his perspective on the timeline of star formation, this recognition marks a significant milestone in a distinguished career that has spanned decades.
Hartmann began looking to the sky as a young child growing up in Cleveland, Ohio. Inspired by the dawn of the space age, he built rockets from balsa wood and cardboard. However, the limited open space in the city often resulted in his rockets getting lost in the trees when they didn’t burn up. Frustrated by these setbacks, his interests began to drift from engineering rockets to studying space itself. At age 13, with the help of his father, he built a telescope that launched a lifelong fascination with the stars and planets.
After obtaining his Bachelor of Science in 1972 at Case Western Reserve University and his PhD in astronomy at the University of Wisconsin four years later, Hartmann joined the Smithsonian Astrophysical Observatory (SAO) at Harvard University as a research scientist, where he remained for nearly thirty years.
In 2005, Hartmann and his wife were hired as professors in the astronomy department at the University of Michigan. Six years later, Hartmann was named Leo Goldberg Collegiate Emeritus Professor of Astronomy in the presence of Professor Goldberg’s family. He appreciated the opportunity to honor the title’s namesake. Hartmann had met Goldberg, a former U-M professor and chair of the astronomy department, several times. He was impressed by Goldberg’s support for keeping national observatories accessible to a broad scientific community at a time when there was pressure to restrict access to university-affiliated scientists. As a graduate student, Hartmann benefited from this broader access while completing his thesis.
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Column density projections with differing initial global rotation input zoomed in on the central 12 pc of the simulation box. Each row shows a run at 5123 resolution with a different amount of initial global cloud rotation, Ωc, where the first row has no initial additional bulk rotation, shown at four different times; 0.6, 1.2, 1.7, and 2.1 Myr. The column densities are normalized to the same value, with sink positions overplotted as gray dots. Source: https://doi.org/10.3847/1538-4357/ab12ce
Described as “half observer, half theorist,” Hartmann uses his understanding of theory to connect his observations in his research. “In astronomy, nature does the experiments. We take what we observe and try to understand it,” he explains. “It’s like a detective story. You see something and wonder what it is.”
Hartmann’s research involves understanding star and planetary formation. In a solar system, planets orbit in the same direction on a plane. Each solar system originates from a rotating disk of gas and dust, which condenses to form planets and stars. Much of his work has involved trying to understand the preconditions of these rotating disks for star and planet formation.
One of Hartmann’s most significant contributions to the field is his perspective on the timeline of star formation, suggesting it occurs several times more rapidly than previously thought. His research indicates that earlier theoreticians overestimated the role of magnetic fields in slowing star formation while underestimating the role of gravity in accelerating it.
Hartmann recently received a NASA Theory Astrophysics Grant to compute high-temperature events in protostar formation. During the formation of a star, matter must be accreted from its circumstellar disk, which will eventually form planets. This accretion of mass converts gravitational potential energy into heat and radiation.
However, protostars are generally observed to be much fainter than predicted by standard theory. Hartmann, together with Scott Kenyon, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics at Harvard University, speculated that the solution lies in intermittent accretion, a process where matter gradually accumulates without accreting rapidly, influenced by non-ideal magnetohydrodynamics (MHD). Because the disk cannot accumulate mass from its protostellar cloud indefinitely, there is an occasional burst of mass accretion when the disk becomes much brighter than its host star. Essentially, the standard theory predicted a steady average luminosity. However, protostars do not emit electromagnetic radiation at a steady rate. Instead, they radiate at lower levels most of the time, interspersed with sudden bursts.
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Evolution of infall zone vortices and spiral features at each epoch: the linear phase of the RWI, the nonlinear phase of the RWI, the end of the infall episode, and postinfall for (left) the fiducial run rd_sheet such that Rc = Rd and infall is sheet like; (center) runs 45_sheet and 75_sheet for inner and outer disk infall, respectively; and (right) runs rd_cloud and rd_stream in which the annulus width ΔR is widened or narrowed compared to the fiducial run. Each panel is in f–r coordinates, 60 au wide, and centered on the infall zone. Vortex centers have normalized, density-weighted vorticity δω ∼ 1, while spiral features are visible as alternating stripes of δω ± 0.1. Source: doi.org/10.3847/1538-4357/ac54a8
Through his NASA Theory Grant, Hartmann will continue to explore this phenomenon, using numerical computations to investigate the mechanisms behind these high-temperature events observed in protostar formation. By applying non-ideal MHD simulations, he aims to uncover how these processes can explain the unexpected heating observed in solar system materials, which have been found to reach one to two thousand degrees, far exceeding the expected few hundred degrees.
“We can’t study the solar system events in real time; we only have a sort of fossil record. By connecting this with the work that I have done on external disks that also have these high temperature events, I can extrapolate what may have happened billions of years ago in the solar system,” Hartmann said.
In 1998, Hartmann published a book titled “Accretion Processes in Star Formation,” while at the SAO. Considered a seminal work in the field, this book distills complex ideas into a comprehensive resource. With its third edition currently in progress, the book details important aspects such as how the higher mass stars formed through large-scale gravitational accretion.
Much of Hartmann’s work has relied on high-performance computing using the campus-wide shared research resource known as the Great Lakes Slurm cluster. He has commended U-M’s foresight in investing in advanced, university-wide computing. Having a central U-M cluster allows researchers to run and monitor their models locally. “When you set up big calculations that can run for months, you don’t want to wait weeks or months to see if something went wrong,” Hartmann explains.
Hartmann’s induction into the National Academy of Sciences underscores his significant impact on the field of astronomy. One of the most rewarding aspects has been the outpouring of congratulations from former students and colleagues, allowing him to reconnect with many respected individuals from his past.
Hartmann’s career, built on curiosity and adaptability, has not only advanced our understanding of space, but has also inspired countless future scientists. As a mentor, he advises the next generation, “Find a problem that is challenging but solvable. Though truly new challenges may be rare, try to approach them from a new angle.” His journey serves as proof that with passion and persistence, the sky is not the limit—it is just the beginning.