Astronomers using archival data from the Hubble Space Telescope have detected the first stellar stream from a globular cluster outside the Milky Way, located in a galaxy roughly 115 million light-years from Earth. According to researchers, this nearly invisible trail of stars offers a new way to map dark matter and study how galaxies form and evolve across the universe.
Detecting the First Extra-Galactic Globular Cluster Stream
The newly discovered stellar stream sits inside UGC 9050-Dw1, an ultra-diffuse galaxy characterized by an extended and extremely faint profile. Researchers worked to model the stream and trace the host galaxy's gravitational field, which allowed them to estimate the total mass of the galaxy and differentiate between visible matter and dark matter.
Ultra-diffuse galaxies provide a unique environment for these discoveries.
Mapping Dark Matter Beyond the Local Group
Finding a faint stellar stream outside the Local Group marks a significant step for observational astronomy. David Martínez-Delgado, an astrophysicist and researcher at the non-profit foundation ARAID at the Centro de Estudos de Física do Cosmos de Aragão in Teruel, Spain, who was not involved in the study, stated that detecting tidal tails in globular clusters in external galaxies was previously thought to be extremely challenging due to small angular sizes and low surface brightness.
Dark matter remains one of the largest open questions in physics, accounting for an estimated 80% to 85% of the universe. While scientists cannot directly observe dark matter, they track its gravitational influence on stars and galaxies. Tjitske Starkenburg, a research assistant professor at the Center for Interdisciplinary Exploration and Research in Astrophysics at Northwestern University in Evanston, Illinois, explained that observing whether stellar streams in other galaxies feature gaps or clusters caused by small concentrations of dark matter will provide stronger evidence for understanding its true nature.
Did you know?
Stellar streams act as cosmic records of galactic history. When a larger galaxy tears apart a smaller dwarf galaxy, the leftover stars stretch into a long trail, preserving the history of that gravitational interaction over billions of years.
Future Telescopes and Upcoming Discoveries
Observing stellar streams has historically been limited because telescopes must maintain the same position over time, a technique that has primarily succeeded within the Milky Way. The Hubble Space Telescope has a relatively narrow field of view, meaning researchers require precise targeting to spot these faint structures.
Upcoming technology aims to expand these searches. Starkenburg pointed to NASA’s Nancy Grace Roman Space Telescope, scheduled for launch later in the month, which will feature a field of view larger than Hubble’s. Researchers expect that wider fields of view and deeper observations will reveal numerous additional stellar streams both within the Milky Way and across distant galaxies.
Frequently Asked Questions
What is a stellar stream?
A stellar stream is a long, thin association of stars that once belonged to a globular cluster or dwarf galaxy, pulled apart by the gravitational forces of a larger host galaxy.
Why is finding a stellar stream outside the Milky Way important?
It allows astronomers to map the gravitational fields and dark matter content of galaxies far beyond our local neighborhood, expanding our understanding of galactic evolution.
What telescope found this stellar stream?
Researchers found the stream by analyzing archival data from the Hubble Space Telescope.
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