Unveiling the Invisible Universe
For decades, the existence of an elusive substance has been a subject of fascination among astronomers. Known as dark matter, it is detectable only through its gravitational influence on visible objects and constitutes approximately 85% of the universe’s total matter. This enigmatic component envelops entire galaxies in expansive spheroids that intertwine to create the cosmic scaffold of our universe.
Yet, the specifics of this grand architecture remain shrouded in mystery. The universe, propelled by a ghostly force termed dark energy, is in a state of perpetual change, expanding at an ever-accelerating pace. To shed light on these dark intergalactic phenomena, a new space telescope is set to launch on 30 August from NASA’s Kennedy Space Center in Florida. The Nancy Grace Roman Space Telescope promises to offer a fresh perspective on the universe, potentially answering some of astrophysics’ most pressing questions.
As Julie McEnery, the project’s lead scientist, eloquently puts it, “By nature, a facility like Roman is a discovery machine. We are going to find rare, unusual, new, and surprising things.” The observatory is named after NASA’s first chief astronomer, Nancy Grace Roman, who played a pivotal role in the advancement of space astronomy.
Mapping the Cosmic Landscape
During its primary mission, which spans five years, the Roman telescope will chart vast expanses of space, creating a comprehensive image of galaxies and dark matter. This endeavour will aid scientists in understanding how the largest formations in the universe evolve over time. By measuring the subtle distortions of light caused by gravity, Roman will track astrophysical structures, thus enabling researchers to study the role of dark energy in cosmic evolution.
McEnery emphasises the significance of this work, stating, “We are not measuring the properties of something in the universe. We are fundamentally understanding how the space we live in operates.” The telescope’s clear and broad vision is expected to identify up to 200,000 new planets, a remarkable increase from the approximately 6,300 confirmed exoplanets to date. While most of these worlds will be detected as they block a portion of their host stars’ light, Roman’s high sensitivity will allow for the identification of an additional 1,000 planets by measuring their gravitational effects on stellar light.
Given the telescope’s impressive resolution and extensive observational area, predicting the full scope of its discoveries is challenging. “The most exciting scientific findings from Roman could be something we can’t even imagine right now,” McEnery notes.
A Complement to the James Webb Space Telescope
In many ways, Roman will serve as a companion to the James Webb Space Telescope. Both instruments primarily observe infrared light and will orbit a location in space known as Lagrange Point 2, nearly one million miles from Earth, where they can effectively shield themselves from the light of the Sun, Earth, and Moon.
However, while the James Webb is designed to delve deep into the cosmos, Roman will adopt a broader perspective. “James Webb is optimised for observing the universe, but only a small portion of the sky. In contrast, Roman can survey a large area of the sky simultaneously,” explains astrophysicist Rachel Mandelbaum from Carnegie Mellon University.
This panoramic view will enable Roman to explore hundreds of millions of stars in search of planets. Like previous missions, the space observatory will primarily identify its targets by looking for planets that transit in front of their host stars—a highly effective technique for locating large planets with short orbits. To uncover other types of worlds, Roman will also employ a method called gravitational microlensing.
Detecting Exoplanets with Innovative Techniques
When two stars align, the light from the background star is distorted and magnified by the gravity of the foreground star. If the foreground star has a planet, Roman will be able to detect the additional magnification caused by the planet’s gravity on the light from behind. “This method allows us to detect planets that are farther from their stars than other techniques,” shares Matthew Penny, an exoplanet researcher at Louisiana State University. “There’s no need for the planet to complete a full orbit to detect it.”
Roman’s sensitivity to gravitational microlensing effects should enable it to discover planets with masses even less than that of Mercury. It will also be capable of identifying rogue planets that have drifted away from their stars or formed independently in the void. By studying these new populations of planets, scientists can gain insights into the conditions that may lead to the formation of a system like ours and, by extension, a planet capable of supporting life like Earth.
Penny remarks, “Our solar system is quite unique, although we are not entirely certain. There are many favourable circumstances within the solar system that make life possible.” Exploring the outer regions of planetary systems will provide crucial pieces needed to complete this cosmic puzzle. The presence of large planets far from a star could facilitate the formation of smaller planets closer to the habitable zone, where conditions may be suitable for liquid water.
Illuminating the Dark Universe
In addition to uncovering many new worlds, Roman will cast its gaze upon over a billion galaxies. It will particularly focus on a population of galaxies that existed between 2 to 6 billion years after the Big Bang. Mandelbaum highlights the investigation into the history and development of cosmic structure: “In the early universe, matter was distributed almost uniformly. However, there were small perturbations or tiny regions that were just slightly more or less dense.”
These slightly denser regions gradually attracted more material, ultimately forming immense clusters of dark matter known as halos. Gas was then funnelled to the centres of these dark matter halos, igniting stars that clustered together to form galaxies. Roman will create an extraordinarily detailed map of visible galaxies and trace the distribution of dark matter with unprecedented accuracy using a technique called weak gravitational lensing.
“Every time a light ray from a galaxy traverses the universe, including various structures, to reach us, the path of that light ray is slightly perturbed,” explains Mandelbaum. By comparing these perturbed light rays from numerous galaxies, scientists can map the cosmic web of dark matter that surrounds and connects galaxy clusters. Comparing the maps generated by Roman with observations of the early universe will allow researchers to investigate how these structures have evolved over time.
Confronting Cosmic Anomalies
In recent years, three notable anomalies have emerged in cosmology. The first is that the universe appears to be expanding faster today than expected, based on models from the immediate post-Big Bang era. The second anomaly indicates that the universe’s matter is distributed more uniformly than anticipated. The third is a surprising recent finding from the Dark Energy Spectroscopic Instrument (DESI) in Arizona, suggesting that dark energy, the force driving the expansion of the universe, may be unexpectedly weakening over time.
These three tensions indicate various aspects where the standard cosmological model may be incomplete. “It’s somewhat intriguing, because there are signs that something is fundamentally wrong,” states McEnery. For each of these unresolved mysteries, Roman will provide invaluable data. Regarding the universe’s expansion rate, the space telescope is expected to capture tens of thousands of supernova explosions—significantly more than have been observed to date. Certain supernovae can be used to measure the current expansion rate of the universe, enabling researchers to calculate this value with greater precision.
The observatory’s large-scale structure maps will also allow researchers to gain a better understanding of the distribution of matter in the universe. Furthermore, its measurements of the gravitational effects of dark matter will offer a detailed picture of how these structures have evolved over time, allowing scientists to verify whether the intensity of dark energy has indeed changed, as suggested by DESI.
Roman’s extensive view of the universe is set to unveil countless new details, and as scientists piece together this vast puzzle, they may revolutionise our understanding of cosmology. “In the past century, we made significant advances in studying the infinitely small with the development of quantum mechanics and the discovery of elementary particles. Perhaps this will be the century of understanding the infinitely large,” concludes McEnery.