by Images created by NASA’s upcoming Nancy Grace Roman Space Telescope could allow scientists to search for dark matter between the stars.
An international team of researchers believe clusters of dark matter could be influencing the gaps in the strings of stars that hang from tightly packed balls of ancient stellar bodies, known as globular clusters.
Until now, astronomers have only been able to study these interstellar streams within the Milky Way, meaning our understanding of them is limited. Roman, which is due to launch in 2027, should be sensitive enough to see these structures in our nearby Andromeda galaxy – and with such data could be disturbed by seeing dark matter, giving clues to astronomers about this unacceptable substance.
“There are stellar streams in our own galaxy, where we see gaps that could be due to dark matter,” Tjitske Starkenburg, a team member and scientist at Northwestern University, said in a statement. “But these gaps can also be formed in other ways.”
Related: The ‘dark force’ theory could solve 2 open cosmic mysteries
The team makes the case that because the Romans noticed gaps in galaxies other than the Milky Way, it will give scientists a better picture of those gaps as a whole. This could ultimately help determine the existence and properties of dark matter clumps.
Read between the lines (or stars, rather)
Dark matter worries scientists because, despite making up an estimated 85% of the matter in the universe, little is thought about it.
Dark matter does not interact with light, meaning it is effectively invisible to our eyes and cannot be made up of the atoms that make up the electrons, protons and neutrons that make up the “everyday” matter we are used to . Think stars, planets, flowers, books. Everything we see with the unaided eye – including our bodies – is made up of such “normal” matter.
However, dark matter interacts with gravity, meaning that the only way scientists can infer its presence is to look at how it affects the subsequent gravity on everyday matter and the all that light.
The evolution of the universe is fortunate because dark matter interacts gravitationally. Some galaxies, for example, are rotating so fast that the gravity of their visible material – the stars, gas, dust and planets – is not enough to prevent them from flying apart.
“We see the effect of dark matter on galaxies,” Christian Aganze, a team member and postdoctoral fellow at Stanford University, said in the statement. “For example, when we model how galaxies rotate, we need extra mass to explain their rotation. Dark matter could provide that mass.”
Hints of dark matter may hang from globular clusters, which often contain millions of stars, as well as loose stellar streams. That’s because scientists think dark matter can “punch holes” in these stellar streams, creating gaps that can be used to infer the nature of this mysterious form of matter.
“The reason is that these currents are the most interesting to see the effects of dark matter clumps,” said Starkenburg. “First of all, these streams ‘live’ in the vast outer regions of the galaxy, where there is very little structure.
“And secondly, these streams are inherently very thin because they were formed from dense clusters of stars, which means you can see gaps or any disturbances much more easily.”
This is not a new idea, but it is one that has not been fully exploited to get to the bottom of the dark matter problem. Current space telescopes and ground-based instruments are limited to searching for dark-matter holes in the small number of star streams hanging from globular clusters within the Milky Way.
From its position about 1 million miles (1.6 million kilometers) from Earth, the Romans will be able to investigate such features in neighboring galaxies, especially Andromeda, for the first time. Its instrument will produce a wide range of images 200 times larger than those produced by the Hubble Space Telescope.
To test this, this team simulated star streams and let them interact with clumps of dark matter, creating gaps as predicted. The scientists then created pseudo-Roman observations of these dark spaces with material punched in stellar streams. They concluded that the Roman will indeed be able to perceive these gaps when he finally opens his eyes to the cosmos.
The Romans will shed more light on a dark matter
The study of stellar streams suspended from globular clusters is not the only dark matter pursuit that the Romans will undertake while studying the universe.
Scientists think that most, if not all, galaxies are covered in haloes of this mysterious material. And these haloes are believed to extend far beyond the visible matter of galaxies. The space telescope will also study the latter, which is named after NASA’s first Astronomy Chief, Nancy Grace Roman, affectionately known as “Hubble’s mother”.
Roman will not only be used to investigate the dark matter halo around Andromeda, but will also investigate the possibility that there may be smaller “sub-haloes” of dark matter around the nearby galaxy.
“We expect that dark matter sub-halos will interact less with globular cluster currents,” said Starkenburg. “If these subhalos are present in other galaxies, we predict that we will see gaps in globular cluster currents that are likely caused by these subhalos.
“That will give us new information about dark matter, including what types of dark matter halos are present and what their masses are.”
RELATED STORIES
— Dark matter may be hidden in the Large Hadron Collider’s particle jets
— ‘Clumps’ of dark matter discovered by exploiting Einstein’s general theory of relativity
— Here’s how NASA’s Roman Space Telescope will search for distant black holes and exoplanets
In addition to participating in this study, Starkenburg is already helping to lay the groundwork for Rome’s dark matter detection work with funding assistance through NASA’s Nancy Grace Space Telescope Research Participation and Support Opportunities program.
“That team plans to model how globular clusters form in stellar streams by developing a much more detailed theoretical framework,” she said. “We will proceed to predict the origin of the global clusters of stream formations and whether these streams will be visible to the Romans.”
The team’s research is detailed in a preprint paper on the arXiv paper repository that has been accepted for publication in The Astrophysical Journal.
