NASA’s Nancy Grace Untangle Roman Space Telescope will study wispy star streams that extend far beyond the apparent edges of many galaxies. Missions like the Hubble and James Webb Space Telescopes would need to gather hundreds of small images to see these structures around nearby galaxies in full. Roman will do it in one snapshot. Astronomers will use these observations to explore the growth of galaxies and the nature of dark matter.
Blue dots speckle the screen in this animation, representing stars at the outer edges of galaxies. It moves to show slightly darker rings, then again to show what Roman could see – the rings, which are streams of stars, are much brighter.
This animation shows simulated stellar streams amidst a realistic background of stars in the Andromeda Galaxy (M31). Current observatories cannot see faint individual stars in and around galaxies, so we can only see the largest stellar streams and only when selecting stars resembling stellar streams in the image. Not only will Roman be able to image individual stars in nearby galaxies – with similar processing, stellar fluxes will appear even larger.
Credits: NASA Goddard Space Flight Center, based on data from Pearson et al. (2019)
Stellar streams look like ethereal wisps of hair extending outward from certain galaxies, drifting peacefully through space as part of the halo – a spherical region surrounding a galaxy. But these stellar flights are signs of an ancient drama on a cosmic scale that serves as a fossil record of a galaxy’s past. Studying them turns astronomers into galactic archaeologists.
“Haloes are mostly made up of stars that have been ripped from other galaxies,” said Tjitske Starkenburg, a postdoctoral researcher at Northwestern University in Evanston, Illinois, who has examined Roman’s potential in this area. . “Roman’s wide and deep images will be sharp enough that we can resolve individual stars in the halos of other galaxies, making it possible to study stellar fluxes in large numbers of galaxies for the first time.”
The simulations support the theory that Untangle galaxies grow in part by engulfing smaller clusters of stars. A dwarf galaxy captured in orbit by a larger one is distorted by gravity. Its stars drizzle, tracing arcs and loops around the greater galaxy until they finally become its newest members.
“As individual stars escape from the dwarf galaxy and fall into the more massive one, they form long, thin streams that remain intact for billions of years,” said Sarah Pearson, Hubble Postdoctoral Fellow at the University. from New York to New York and the lead author of a separate study on the mission’s projected observations in this area. “Thus, stellar streams hold secrets of the past and can shed light on billions of years of evolution.”
Astronomers have caught this cannibalistic process in the act by using telescopes like the ESA’s (European Space Agency) Gaia satellite, which is fine-tuned to measure the positions and motions of stars in our Milky Way galaxy. Roman will extend these observations by making similar measurements of stars both in the Milky Way and in other galaxies.
The Milky Way is home to at least 70 stellar streams, which means it’s likely eaten at least 70 dwarf galaxies or globular star clusters – groups of hundreds of thousands of gravity-bound stars. Roman’s Milky Way images could allow astronomers to string together snapshots in time to show the movement of stars. This will help us understand what dark matter is made of – invisible matter that we can only detect by its gravitational effects on visible objects.
One theory suggests that dark matter is “cold” or made up of heavy, slow-moving particles. If so, it should clump together in galactic halos, disrupting stellar streams in ways Roman could see. By detecting or eliminating these distortions, Roman could narrow down the candidates for dark matter composition.
Astronomers are also eager to study Untangle stellar fluxes in several of the nearby Milky Way galaxies. They are not well studied in other galaxies because they are so faint and so far away. They are also so vast that they can wrap around an entire galaxy. It takes an unparalleled panoramic view like Roman’s to capture images that are both large and detailed enough to see.
A series of images showing wispy stellar streams surrounding eight individual galaxies. The light and dark are reversed so that the background is gray-white and the galaxies appear as black specks. Extending from each like tentacles are streams of stars.
This series of images shows how astronomers find stellar fluxes by reversing light and dark, similar to negative images. Color images of each of the nearby galaxies shown are included for context. The galaxies are surrounded by huge halos of hot gas dotted with sporadic stars, believed to be the shadow regions that surround each galaxy here. Roman could enhance these observations by resolving individual stars to understand the stellar populations of each stream and see stellar streams of different sizes in even more galaxies.
Credits: Carlin et al. (2016), based on images by Martínez-Delgado et al. (2008, 2010)
Particularly elusive stellar streams that formed when the Milky Way siphoned stars from globular star clusters have been detected before, but they have never been found in other galaxies. They are fainter because they contain fewer starbursts, making them much harder to spot in other, more distant galaxies.
Roman could detect them in several of our neighboring galaxies for the very first time. The mission’s wide, sharp and deep view should even reveal individual stars within these huge dark structures. In a previous study, Pearson led the development of an algorithm to systematically search for stellar fluxes from globular clusters in nearby galaxies.
Starkenburg’s new study adds to the picture by predicting that Roman should be able to detect dozens of streams in other galaxies from dwarf galaxies, providing unprecedented insight into galaxy growth.
Unravel exciting to learn more about our Milky Way, but if we really want to understand galaxy formation and dark matter, we need a larger sample,” Starkenburg said. “Studying stellar fluxes in other galaxies with Roman will help us get the big picture.”
The Roman Nancy Grace Space Telescope is operated at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation from NASA’s Jet Propulsion Laboratory and Caltech/IPAC in Southern California, the Space Telescope Science Institute in Baltimore, and a scientific team composed of scientists from various research institutions. Untangle’s primary industry partners are Ball Aerospace and Technologies Corporation in Boulder, Colorado; L3Harris Technologies in Melbourne, Florida; and Teledyne Scientific & Imaging in Thousand Oaks, California.