NASA has selected the University of Arizona to lead one of its four inaugural Astrophysics Pioneers missions. Funded at $20 million, the Aspera mission will study galaxy evolution with a space telescope barely larger than a mini fridge. The telescope will allow researchers to observe galaxy processes that have remained hidden from view until now.

Led by principal investigator Carlos Vargas, a postdoctoral researcher in UArizona's Steward Observatory, the Aspera mission seeks to solve a longstanding mystery about the way galaxies form, evolve and interact with each other. Intended for launch in late 2024, the space telescope is being specifically designed to see in ultraviolet light, which is invisible to the human eye.

NASA chose Aspera and three other missions for further concept development in the agency's new Pioneers Program for small-scale astrophysics missions.

The Aspera mission's goal is to provide the first-ever direct observations of a certain portion of the circumgalactic medium – vast "oceans" of low-density gas that permeate and surround individual galaxies and in some cases even connect them, bridging large distances across the universe.

The familiar pictures of galaxies as luminous archipelagos floating in space, filled with millions or billions of stars, tell only a small part of their story, Vargas said.

"As telescopes have become more sensitive and have allowed us to discover more exotic types of gases, we now realize there is tons of stuff in between galaxies that connects them," he said. "Galaxies are undergoing this beautiful dance in which inflowing and outflowing gases balance each other."

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Processes such as supernova explosions blow gas out of the galaxy, and sometimes it rains back down onto the galactic disc, Vargas said.

Previous observations of the circumgalactic medium, or CGM, revealed that it contains several different populations of gas in a wide range of densities and temperatures astronomers refer to as phases. But one of these gas phases has eluded previous attempts at studying it, and Vargas said it's important because it is believed to host most of a galaxy's mass.

"There is this intermediate form we refer to as warm-hot, and that is particularly interesting because it provides the fuel for star formation," he said. "No one has been able to successfully map its distribution and really determine what it looks like."

The Aspera mission is designed to home in on that missing chunk of the CGM that astronomers know must be there but haven't been able to observe.

"Aspera is an exciting mission because it will lead us to discover the nature of mysterious warm-hot gas around galaxies," said Haeun Chung, a postdoctoral research associate at Steward Observatory.

As the mission's project scientist, Chung leads the instrument team charged with building the new space telescope.

"Though small, Aspera is designed to detect and map faint warm-hot gas, thanks to recent technological advancements and the increased opportunity that small-sized space missions provide," Chung said.

Because the portion of the CGM that researchers refer to as warm-hot is thought to host the lion's share of the mass that makes up a galaxy, it is a crucial piece of the puzzle for understanding how galaxies form and evolve, Vargas said.

"If you care about how life evolved, you care about how galaxies evolve, because you can't have a planet without a star, and you can't have a star without galaxy," he said. "These all are very interconnected."

The Aspera telescope will be the only instrument in space capable of observing in the ultraviolet spectrum, with the exception of the Hubble Space Telescope, which has surpassed its expected mission lifespan by many years.

Vargas said his team chose the mission's name, Latin for "hardship," to highlight the extraordinary difficulties that have needed to be overcome to observe and study the CGM.

"People have been going for this 'missing' gas phase for decades," he said. "We aptly named our telescope to honor their efforts."

UArizona President Robert C. Robbins said the mission marks a new milestone in the university's long history of space exploration.  

"Being selected for the first iteration of NASA's Astrophysics Pioneers program is a testament to our excellent track record in space exploration – from providing the scientific approaches needed to tackle some of the most challenging questions in the universe, to developing innovative technology and providing successful management throughout the project," he said.

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Elizabeth "Betsy" Cantwell, UArizona senior vice president for research and innovation, applauded Vargas's leadership of the mission.

"Dr. Vargas's leadership on the Aspera mission reflects the excellent caliber of researchers attracted to the University of Arizona. We are particularly pleased because Dr. Vargas represents the exemplary nature of scientific inquiry at a Research 1 Hispanic-Serving Institution like the University of Arizona," she said. "To receive this prestigious award so early in his career demonstrates Dr. Vargas's incredible capability, and I am thrilled to see our researchers expanding our understanding of a subject as fundamental as galaxy formation and evolution."

Cantwell added that the newly launched University of Arizona Space Institute provided the research team with support, and it will be building support for other large and impactful space initiatives as the institute grows. 

"I'm tremendously proud to be part of a university that encourages and supports early career scientists like Carlos Vargas and Haeun Chung – both post-doctoral researchers – and the faculty members and engineers in their team, to successfully compete for ambitious missions like Aspera," said Steward Observatory Director Buell Jannuzi.

Aspera brings together an interdisciplinary and diverse team including researchers from Columbia University, the University of Iowa, and Ruhr University in Bochum, Germany. The UArizona team includes deputy principal investigator Erika Hamden, assistant professor of astronomy and assistant astronomer at Steward Observatory; mission manager Tom McMahon, head of Steward Observatory's engineering group; Peter Behroozi, assistant professor of astronomy; Ewan Douglas, assistant professor of astronomy; Dennis Zaritsky, professor of astronomy and deputy director of Steward Observatory; Aafaque Raza Khan, a graduate student at Steward Observatory; Dae Wook Kim, assistant professor in the College of Optical Sciences; and Simran Agarwal, graduate student in the College of Optical Sciences.

Corporate mission partners are Tucson-based companies Blue Canyon Technologies, a subsidiary of Raytheon Technologies, and Ascending Node Technologies.