Astronomers have discovered a faint stream of stars in another galaxy for the first time, opening a new way to investigate one of the universe’s biggest mysteries: dark matter.
The newly discovered structure is known as a globular cluster stellar stream.
These streams form when groups of stars called globular clusters are gradually pulled apart by gravity.
As stars escape, they can form long, narrow trails that stretch across a galaxy.
Astronomers are particularly interested in these streams because their shapes and movements preserve clues about the gravitational forces they have experienced.
This means scientists can use them to investigate dark matter, an invisible form of matter that cannot be seen directly but can be detected through its gravitational effects.
Until now, globular cluster stellar streams had only been observed within our own Milky Way.
An international research team led by Ph.D. student Julie Kiel Holm from the Niels Bohr Institute has now identified one in another galaxy.
The discovery, reported in Nature, shows that a technique previously limited to the Milky Way could potentially be used to study dark matter in many other galaxies.
Finding the stream was especially difficult because these structures are extremely faint. The newly discovered stream is also located in an ultra-diffuse galaxy called UGC9050-Dw1.
Ultra-diffuse galaxies are unusually faint and spread out, making them difficult to study. Some can contain large amounts of dark matter despite producing relatively little visible light.
The combination of a very faint stellar stream and a very faint galaxy makes the detection particularly remarkable.
The researchers did more than simply identify the stream. They also used it to estimate how mass is distributed throughout UGC9050-Dw1. Their results indicate that the galaxy contains a large amount of dark matter, consistent with previous studies.
Dark matter is thought to account for most of the matter in the universe, yet scientists still do not know what it is made of. Because it does not emit, absorb or reflect light, researchers must study it indirectly by observing how its gravity affects stars, galaxies and other visible objects.
Stellar streams provide an especially useful tool because their long, thin shapes can be disturbed by gravitational forces. By studying their structure and movement, astronomers can reconstruct the gravitational environment through which they have traveled.
Until this discovery, however, scientists could only apply this method to globular cluster streams inside the Milky Way. Finding one elsewhere greatly expands its potential.
Although the new study examines only one galaxy, the researchers believe the method could eventually be applied to many different types of galaxies. Comparing stellar streams across different environments could provide a much broader picture of how dark matter is distributed and behaves throughout the universe.
Future space telescopes could make that possible. The European Space Agency’s Euclid telescope and NASA’s upcoming Nancy Grace Roman Space Telescope are designed to observe huge areas of the sky with exceptional sensitivity.
As these observatories collect more data, astronomers expect to discover many more faint stellar streams beyond the Milky Way.
Those delicate trails of stars could ultimately become powerful cosmic maps, revealing the hidden dark matter that shapes galaxies across the universe.
Source: KSR.
