A group of astronomy students from the University of Texas, collaborating between the Austin and San Antonio campuses, has made a significant discovery that has been published in a scientific journal. Their research focused on Segue 1, a small galaxy located approximately 75,000 light-years from Earth, which has long been thought to be dominated by dark matter, an elusive substance that does not emit light. However, the new findings suggest that this dim dwarf galaxy contains a previously unidentified supermassive black hole, which is responsible for most of its mass, rather than dark matter.
The supermassive black hole is estimated to have a mass greater than 450,000 times that of the Sun. Nathaniel Lujan, a graduate student from San Antonio, utilized advanced computer modeling techniques learned in his Galactic and Gravitational Dynamics course to aid in the discovery of this cosmic entity hidden within Segue 1. This revelation implies that supermassive black holes may be more common in smaller galaxies than previously believed, prompting a re-evaluation of current understandings regarding the structure and stability of dwarf galaxies.
“It”s amazing,” Lujan stated during a presentation at the American Astronomical Society meeting held in Anchorage, Alaska. “Despite Segue 1 being almost invisible, I”m proposing that it hosts a supermassive black hole weighing half a million solar masses at its core.”
Initially detected in 2006 by the Sloan Digital Sky Survey telescope in New Mexico, Segue 1 was considered too sparse in stellar content to generate the gravitational forces necessary to maintain its structure. Scientists had theorized that a surrounding dark matter halo was preventing the galaxy from disbanding. The students began their investigation of Segue 1 as part of a homework assignment, explained Karl Gebhardt, a professor of astronomy at UT Austin, who co-taught the course with assistant professor Richard Anantua. The aim was to teach students how to conduct computer simulations to infer unseen phenomena.
Although black holes themselves are invisible, astronomers can detect them by observing the glowing gas surrounding them and the gravitational shadows they cast. Given Segue 1″s known dark matter content, it served as a fitting subject for their simulation exercise. The students were divided into three teams: one focused on dark matter, another considered a theoretical black hole, and the third examined the galaxy”s star population. The objective was to determine which model best matched the actual star behavior within the galaxy.
The group first filtered out stars influenced by the gravitational pull of the Milky Way, allowing them to isolate those stars genuinely affected by Segue 1″s gravity. Their analysis revealed that stars near the center of the galaxy exhibited fast, compact orbits, indicating they were circling a black hole. The models that included the black hole yielded the most accurate representation of the observed star movements. “I did not expect that,” Gebhardt remarked. “I thought, “We need to write this up.”” The results of their research were recently published in The Astrophysical Journal Letters, with several students from the spring 2024 class credited as co-authors.
Black holes are enigmatic regions in the universe where gravity is so intense that not even light can escape. Just a few decades ago, their existence was a topic of debate, yet the Event Horizon Telescope successfully captured the first image of a black hole in the Messier 87 galaxy in 2019. Black holes are defined by their event horizon, a boundary beyond which nothing can return. The students were surprised to discover that the central black hole”s mass could be around ten times that of all the stars within Segue 1 combined. Typically, stars in a galaxy outweigh their central black hole.
Lujan suggested that Segue 1 might be misleading observers, stating, “It could have started as a much larger galaxy, but due to its close interactions with the Milky Way, it may have lost gas and its star formation capabilities.” For his doctoral thesis, Lujan intends to apply advanced computing and artificial intelligence to conduct further simulations on other dwarf galaxies believed to be dominated by dark matter. Meanwhile, research teams have speculated that the small red dots found in the early universe could be massive gas spheres encircling black holes, termed “black hole stars.” One hypothesis posits that Segue 1 may resemble a new type of galaxy identified by NASA”s James Webb Space Telescope, which are believed to feature vast black holes with limited stellar populations.
This study serves as a crucial reminder that fresh insights can emerge by reevaluating existing data, according to Gebhardt. “What excites me is that galaxies like Segue 1 may offer analogs to the early universe, where black holes were significantly massive,” he emphasized. “Regardless of our past assumptions about their formation, nature has discovered a way.”
