The cosmic hopping path leads astronomers to discover another galaxy

A faint streak of stars in a distant galaxy has led astronomers to a discovery that could reveal secrets about one of the universe’s greatest mysteries.

Hidden within the Hubble Space Telescope’s archival data, researchers have found a barely visible trace of stars — The first globular cluster star stream outside the Milky Way has been discovered. This celestial phenomenon, located in a galaxy about 115 million light-years from Earth, is the remains of a dense ball of stars that is slowly being pulled down by the gravity of its host galaxy. When the cluster loses stars, the remnants form a long, narrow stream.

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Astronomers have discovered dozens of stellar streams within the Milky Way, but because these trails are faint and difficult to detect, there are likely many more that have gone undetected. Now, with evidence of them occurring in other galaxies, astronomers may be able to use them as cosmic tracers to better understand how galaxies form and evolve.

This finding, which was detailed in a study published on Wednesday In the journal NatureIt also allowed the team of astronomers to map the galaxy – known as UGC 9050-Dw1 – and its gravitational field through flow modeling.

Because the galaxy’s gravity affects the shape and movement of the stellar stream, researchers used star trails to track the galaxy’s gravitational field. Through their models, they were also able to estimate the total mass of the galaxy, how much of it is made up of visible objects, such as stars, and how much is made up of dark matter, a mysterious form of matter that cannot be seen but has gravity.

When the study team began to realize they had found a stellar stream outside our galaxy, “it was very exciting,” said co-author Julie Kjell-Holm, a doctoral fellow at the Niels Bohr Institute at the University of Copenhagen in Denmark, who studies globular clusters and the formation of stellar streams. “Then we looked at each other and asked: Where do we go from here?”

Dark matter intrigues scientists because they don’t know what it is, yet they can see the effect of its gravity on stars and galaxies. “About 80% to 85% of our universe we think of is dark matter, and that makes it very tempting to try to figure out what that is,” Kjell-Holm added.

Stellar streams have been used to help scientists map the dark matter within our galaxy. Now, these same tools can be used to help better understand the composition of dark matter and the structure of other galaxies that share the universe.

Discovery of stellar streams

The newly discovered stream is located within a very diffuse galaxy, which is very diffuse and faint, making the stellar stream easy to detect, the study’s authors speculated.

“At the same time, these super-diffuse galaxies are thought to be very massive, and they have to be massive to be able to actually pull stars out of that parent cluster,” said Sarah Persson, co-lead author and associate professor at DTU Space, the National Space Institute at the Technical University of Denmark.

“So those two things together — the fact that it provides a faint background, but also has a tidal field strong enough to pull stars out of the cluster — is a great combination if you want to find one,” she added.

When trying to identify these currents, astronomers look for thin, elongated structures on their telescopes. Streams can also be traced by their movement along the sky; However, doing so requires the telescope to be in the same position over time, and the technique has so far only been able to find stellar streams in the Milky Way.

“The area that Hubble can see is actually not very large,” said study co-author Tjitsky Starkenberg, a research assistant professor at the Center for Interdisciplinary Exploration and Research in Astrophysics at Northwestern University in Evanston, Illinois. “So you would have to be very, very lucky to be able to see that, and we don’t really know where to look to target it essentially.”

The study’s authors expect that future developments in the telescope will allow further detection of these clusters inside and outside our galaxy. Starkenberg pointed to NASA’s Nancy Grace Roman Space Telescope, which is expected to launch at the end of the month and will have a larger field of view, “like 100 Hubbles in one image.”

Faint stellar stream detected in an extragalactic galaxy Local group A galactic neighborhood of more than 50 galaxies bound together by gravity is a remarkable thing, David Martinez Delgado, an astrophysicist and researcher at the nonprofit ARAID at the Aragon Center for the Study of Cosmic Physics in Teruel, Spain, said in an email. Martinez-Delgado was not involved in the new study.

“I had previously thought that detecting globular cluster tidal tails in outer galaxies would be very difficult, given their small angular size and very low surface brightness,” he added. “This result shows that with sufficiently deep and high-resolution observations, these structures may be detectable well outside the Local Group.”

Record of galactic evolution

Stellar streams can serve as records of a galaxy’s past, giving astronomers clues about how galaxies have changed over time. When a larger galaxy pulls down a smaller dwarf galaxy, the dwarf stars can expand to form a stream — a cosmic artifact from that encounter.

Incoming jets from globular clusters, like the one described in the study, preserve this history on a smaller scale, revealing how the mass traveled through its host galaxy and how the galaxy’s gravity gradually separated it. By tracing this history, researchers can then learn how the galaxy’s mass is distributed, including the invisible dark matter that makes up its gravitational field.

Observing the first globular cluster star stream outside the Milky Way opens the door to discovering more such phenomena in galaxies across the universe. The study’s authors said they hope future discoveries will help reveal more secrets about other galaxies as well as the dark matter within them.

The researchers pointed out that one feature that deserves further investigation is the gaps or clumps in stellar streams that scientists assume develop when small concentrations of dark matter pass through them. “But there are other things that can cause some of these similar effects,” Starkenberg said.

Finding more jets, perhaps in other galaxies, and observing whether they contain similar gaps or clumps, “is a much stronger argument for it having to be dark matter,” Starkenberg added.

Pearson noted that many questions remain about dark matter even though its existence has been known for nearly a century.

“It’s actually one of the biggest open questions in physics,” she said. “What is the nature of dark matter? Is it a particle? Is it a lot? Is it something completely different? We don’t know.”