Images created by NASA’s upcoming Nancy Grace Roman Space Telescope may allow scientists to search for dark matter among stars.
An international team of researchers believes that gaps in the chains of stars dangling from tightly packed balls of ancient stellar objects, called globular clusters, could be affected by clumps of dark matter.
Until now, astronomers have only been able to study these dangling stellar streams within the Milky Way, which means our understanding of them is limited. ROMAN, scheduled to launch in 2027, should be sensitive enough to see these structures in our neighboring galaxy Andromeda – and in such detail it will be possible to see perturbations caused by dark matter, giving astronomers clues about this elusive matter.
“There are stellar streams in our galaxy, where we see gaps that may be due to dark matter,” team member and Northwestern University scientist Tjitski Starkenberg said in a statement. “But these gaps can also be shaped by other means.”
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The team emphasizes that while Roman observes gaps in galaxies other than the Milky Way, it will provide scientists with a better picture of these gaps as a whole. This could ultimately help determine the existence and properties of dark matter clumps.
Reading between the lines (or rather the stars)
Dark matter is troubling to scientists, because although it represents an estimated 85% of the matter in the universe, they have very little idea what it is.
Dark matter does not interact with light, which means it is virtually invisible to our eyes and cannot be composed of the atoms made up of electrons, protons and neutrons that make up the “everyday” matter we are used to. Think stars, planets, flowers and books. Everything we see with the naked eye – including our bodies – is made of this “natural” substance.
However, dark matter interacts with gravity, meaning that the only way scientists can infer its existence is by looking at how its effect on gravity subsequently affects all matter and everyday light.
The fact that dark matter interacts with gravity is actually fortunate for the evolution of the universe. Some galaxies, for example, spin so fast that the gravity of their visible matter — stars, gas, dust, and planets — wouldn’t be enough to keep them from being blown apart to any great extent.
“We see the influence of dark matter on galaxies,” Christian Aganzi, a member of the team and a postdoctoral fellow at Stanford University, said in the statement. “For example, when we model how galaxies rotate, we need additional mass to explain their rotation. Dark matter may provide that missing mass.”
Clues about dark matter may dangle from globular clusters, which often contain millions of stars, along with loose stellar streams. This is because scientists believe dark matter can “poke holes” in these stellar streams, creating gaps that can be used to assess the nature of this mysterious form of matter.
“The reason these streams are more interesting to see the effects of these dark matter clumps is two-fold,” Starkenberg said. First, these streams “live” in the extreme outer regions of the galaxy, where there is very little structure.
“And secondly, these streams are intrinsically very thin because they are formed from dense clusters of stars, which means you can see gaps or any disturbance more easily.”
This is not a new idea, but it is one that has not been fully exploited to solve the dark matter problem. Current space telescopes and ground-based instruments are limited to searching for holes punched by dark matter in a small number of stellar streams dangling from globular clusters within the Milky Way.
From his location about 1 million miles (1.6 million kilometers) from Earth, Roman will be able to explore such features in neighboring galaxies, especially Andromeda, for the first time. Its wide-field instrument will produce images 200 times larger than those created by the Hubble Space Telescope.
To test this, this team simulated streams of stars and allowed them to interact with clumps of dark matter, generating holes as expected. Scientists then created fictitious Roman observations of these spaces perforated by dark matter in stellar streams. They conclude that Roman will indeed be able to discover these gaps when he finally opens his eyes to the universe.
Romans will shed more light on dark matter
Studying the stellar streams dangling from globular clusters will not be the only search for dark matter that Roman engages in as he studies the universe.
Scientists believe that most, if not all, galaxies are covered in halos of this mysterious substance. These halos are thought to extend beyond the visible matter contents of galaxies. The latter will also be studied by the space telescope, named after NASA’s first chief astronomer, Nancy Grace Roman, who is known as the “Mother of Hubble.”
Not only will Roman be used to investigate the dark matter halo around Andromeda, but it will also investigate the possibility of smaller “subhalos” of dark matter around the nearby galaxy.
“We expect smaller subhalos of dark matter to interact with globular cluster currents,” Starkenberg said. “If these subhalos exist in other galaxies, we expect that we will see gaps in the globular mass streams that are likely caused by these subhalos.
“This will give us new information about dark matter, including what types of dark matter halos exist and what their mass is.”
In addition to his participation in this study, Starkenberg is already helping to lay the foundation for Roman’s work investigating dark matter with the help of funding through NASA’s Nancy Grace Roman Space Telescope Research Participation and Support Opportunities Program.
“This team plans to model how globular clusters form in stellar streams by developing a more detailed theoretical framework,” she said. “We will continue to predict the origins of globular clusters that form a stream and whether these streams can be observed using Romans.”
The team’s research is detailed in a preprint paper located in the arXiv paper repository and has been accepted for publication in The Astrophysical Journal.