In the research lab of Rhodes College Physics professor Dr. David Rupke, students have been exploring galaxy evolution by using NASA-sponsored telescopes to collect data. Now Rupke and his team, including Triet Ha ’25, Shane Caraker ‘24, and Jack Harper ’25, have taken images of the massive galaxy Makani using NASA’s Hubble Space Telescope (Hubble) and detected ionized oxygen atoms in the galactic wind of Makani that could serve as a benchmark for the next generation of NASA’s ultraviolet telescopes.
Rupke participated in a Jan. 15th news conference of the American Astronomical Society, shedding light on the Rhodes team’s astronomy research. More than 3,600 astronomers and affiliates attended the 245th meeting of the organization, held in National Harbor, MD.
In his presentation, “Growing in the Wind: Watching a Galaxy Seed Its Environment,” Rupke highlighted images taken with Hubble, which is presently the only telescope that can capture ultraviolet images of the universe. Very little ultraviolet light penetrates the Earth’s atmosphere, so a space telescope is needed.
Galaxies are home to the stars and to massive black holes at their centers. These stars and black holes power galactic winds, which seed a galaxy’s environment with hydrogen gas and the heavy elements produced by stars. This environment, called the circumgalactic medium (CGM), is a tenuous but enormous reservoir of gas around a galaxy. Observations of the various states of oxygen in the CGM can provide an understanding of how a galaxy sustains the growth of its CGM, but these observations are difficult to obtain. Much of scientists’ knowledge of the CGM in galaxies has been derived from statistical studies (not images) of the CGM’s warm-hot phase (temperatures above 100,000 Kelvin).
The Rhodes team has been studying the warm-hot phase of the Makani galaxy, whose CGM was first detected in 2019. According to Rupke, Makani’s enormous and luminous oxygen nebula has made it an ideal target to image, and it is providing one of the first direct windows into how a galaxy contributes to the ongoing formation and chemical enrichment of its CGM.
The Rhodes team captured ultraviolet images of Makani in 2020 and 2021 using Hubble. Ha, Caraker, Harper, and Rupke carefully analyzed these images, searching for signs of the nebula in the light of oxygen ionized five times at wavelengths near 100 nanometers. In collaboration with researchers from other institutions, the Rhodes team detected the faint signal of this warm-hot phase for only the second time in the CGM of a galaxy. Models and computer simulations of the interactions of a galaxy’s wind with its CGM find that this emission comes from hot gas that is cooling off. This may cause the cool clouds in the wind to grow, rather than disintegrate, in the wind.
“Imaging the warm-hot gas around a galaxy is really a holy grail of CGM research, so it’s exciting to be able to push Hubble to its limits and make this detection,” said Rupke. “The Rhodes undergraduates I worked with were absolutely critical to making this happen, and it’s a real pleasure to see them play a major role in world-class research.”
According to Rupke, detecting the warm-hot CGM in emission is one of the scientific goals of the proposed Habitable Worlds Observatory, which would be the first infrared/optical/ultraviolet telescope designed specifically to search for signs of life on planets orbiting other stars. “Thus, our detection of oxygen plus five in the galactic wind of Makani serves as a benchmark for the next generation of ultraviolet telescopes,” he said.
In addition, Rupke and the Rhodes team have submitted their research for publication in the flagship journals of the American Astronomical Society.
Learn more about physics at Rhodes.