Leo P, a small galaxy and a distant neighbor of the Milky Way, is paving the way for astronomers to gain insights into how stars are formed and how galaxies evolve.
A recent study in the Astrophysical Journal led by Kristen McQuinn, a researcher at the Space Telescope Science Institute and an associate professor at Rutgers University-New Brunswick’s Department of Physics and Astronomy, reveals that Leo P has “reignited.” This means it became active again during a crucial era in the universe’s history, creating stars while many other smaller galaxies remained dormant.
By examining galaxies in their formative phases and across various environments, astronomers hope to achieve a richer understanding of the universe’s origins and the essential processes that shape it.
McQuinn and her research team utilized NASA’s James Webb Space Telescope, an advanced space instrument equipped with a large segmented mirror and an expansive sunshield, which allows for the capture of intricate images of far-off celestial bodies.
Discovered by McQuinn and her colleagues in 2013, Leo P is a dwarf galaxy located approximately 5.3 million light-years from Earth. It is sufficiently distant from the Local Group—a collection of galaxies including the Milky Way—so it can be considered a neighbor without being influenced by the gravitational forces of larger galaxies.
Sitting in the Leo constellation, Leo P is comparable in size to a star cluster within the Milky Way and shares a similar age with it. The “P” in Leo P stands for “pristine,” signifying that it contains very few elements apart from hydrogen and helium.
“Leo P serves as an exceptional platform for detailed exploration of the early evolution of a low-mass galaxy,” McQuinn said, who is also in charge of the Science Operations Center for the Nancy Grace Roman Space Telescope at the Space Telescope Science Institute in Baltimore.
The research team delved into the galaxy’s history. The stars identified by the telescope are roughly 13 billion years old, acting as “fossil records” of ancient star formation activities. “Instead of examining stars as they form in their original locations in the early universe, we analyze the stars that have endured through cosmic time and utilize their characteristics today to infer past events,” McQuinn explained.
They discovered that Leo P initiated star formation early on, only to halt for several billion years. This pause coincided with the Epoch of Reionization. It wasn’t until billions of years later that the galaxy reignited and resumed producing new stars.
“We only have similar measurements for three other isolated galaxies, and they display a comparable pattern,” McQuinn noted.
Observations of dwarf galaxies within the Local Group, on the other hand, indicate that their star formation ceased during this epoch.
The Epoch of Reionization, recognized by astronomers as a pivotal timeframe in the universe’s development, occurred approximately 150 million to one billion years after the Big Bang, marking the formation of the first stars and galaxies.
The differences in star formation among dwarf galaxies provide strong evidence that a galaxy’s mass at the time of reionization isn’t the sole factor affecting whether star production stops. The galaxy’s environment—such as being isolated or part of a larger system—also plays a crucial role, McQuinn remarked.
McQuinn emphasized that these observations will clarify not only when smaller galaxies formed their stars but also how the universe’s reionization may have influenced the formation of these smaller structures.
“If this trend continues, it offers valuable insights into the growth of low-mass structures, which are essential for understanding structure formation and serve as a benchmark for cosmological simulations,” she explained.
The research findings also revealed that Leo P is metal-poor, containing only 3% of the sun’s metallicity. This fact means the stars within this dwarf galaxy have 30 times fewer heavy elements compared to the sun, which makes Leo P resemble the primordial galaxies from the early universe.
The knowledge gained from these findings will assist astronomers in constructing a timeline of cosmic events, understanding how small structures developed over billions of years, and uncovering the processes leading to star formation, McQuinn added.
The study also included contributions from fellow Rutgers scientists Alyson Brooks, an associate professor; Roger Cohen, a postdoctoral associate; and Max Newman, a doctoral student— all affiliated with the Department of Physics and Astronomy.
