[BizHanKook] Another space telescope, following in the footsteps of Hubble and James Webb, has set its sights on the universe. The Nancy Grace Roman Space Telescope was launched aboard a Falcon Heavy rocket from Launch Complex 39A at the Kennedy Space Center on August 30 (local time).
Simply put, the Roman Space Telescope is equipped with an eye the same size as Hubble's but can view a patch of the sky approximately 100 times larger. It scans the vast universe so rapidly that it can accomplish in just one month an observation scale that would have taken Hubble 100 years to complete. Its fundamental purpose differs from existing space telescopes, which are designed to peer deeply into a single specific celestial object.
Nancy Grace Roman, the Mother of Hubble
Nancy Grace Roman led NASA's space astronomy program in 1959, back when the very concept of a space telescope was unfamiliar and received with skepticism. She played a pivotal role in making the great dream that would eventually lead to the Hubble Space Telescope a reality by securing difficult approval from Congress. For this reason, she is often called the "Mother of Hubble."
The telescope, now known as the Roman Space Telescope, originally had a much more mundane name. It was called WFIRST (Wide Field Infrared Survey Telescope), signifying its mission to observe the infrared universe with a wide field of view. However, after Nancy Roman passed away in 2018, the telescope was renamed in her honor to celebrate her achievements. The person who contributed to the birth of Hubble will now look out at the universe under the name of yet another space telescope.
Viewing a Sky 100 Times Larger with a Mirror the Same Size as Hubble
The diameter of Roman's primary mirror is exactly 2.4 meters, the same as Hubble's. Compared to the James Webb Space Telescope, which features a much larger primary mirror made of several segmented mirrors, it might feel like a smaller telescope. However, the essence of Roman lies not in the size of the mirror, but in its optical system and observation method.
While Hubble is specialized for looking deeply and precisely into narrow portions of the sky, Roman is designed to observe much wider areas at once with the same level of precision.
In standard telescopes, the collected light is sharpest at the center of the field of view. Conversely, because Roman must capture an extremely wide field of view all at once, its optical system is configured to maintain uniform image quality across a broad area surrounding the center. The detectors are also not simply clustered in the middle of the field; they are arranged to efficiently cover the wide focal plane.
Roman's Wide Field Instrument camera is approximately 300 megapixels. The size of the sky covered by a single pixel is about 0.11 arcseconds, and the area captured in one shot is larger than the full moon. Compared to Hubble's field of view, it is nearly 100 times larger.
However, simply widening the field of view does not solve every problem. With a narrow view, one only needs to focus on a target object at the center, but as the field widens, the number of stars and galaxies entering the frame increases dramatically. Celestial objects must appear with consistent clarity regardless of their position in the frame, and starlight must be captured stably across the entire wide focal plane. Roman is packed with sophisticated optical technology specifically designed to achieve this.
Why Is Roman Needed?
Even with Hubble, James Webb, and several other space telescopes already in operation, the reason for needing the new Roman telescope is clear: its role is completely different from existing telescopes.
At any given point, the area Roman can observe covers about 59% of the entire sky. Rather than a telescope like Hubble that observes individual distant objects deeply for long periods, Roman is more of a survey telescope, quickly sweeping the wide sky to find various celestial objects and phenomena such as supernovae, exoplanets, and galaxies.
Once Roman spots a peculiar object while surveying the wide sky, Hubble or James Webb can then observe that target more deeply and clearly. This creates an efficient division of labor between Roman, which discovers targets over large areas, and Hubble/Webb, which peer precisely at specific objects.
In this sense, Roman’s mission is somewhat similar to the European Space Agency's Euclid space telescope, which launched previously. Euclid observes a vast sky area of about 15,000 square degrees. While Roman’s survey area is smaller, it views the universe with higher spatial resolution.
The Vera C. Rubin Observatory in Chile, which recently began full-scale observations, also rapidly scans the visible-light sky with its massive 3.2-gigapixel camera. While the Rubin Observatory has a much wider field of view than Roman, it is a ground-based telescope and cannot be free from atmospheric interference. Instead, Rubin observes the same sky in visible light, while Roman observes it in near-infrared. By combining these datasets, researchers can compare the characteristics of numerous celestial objects as they change across different wavelengths.
The massive cosmic map that Roman will construct will play a critical role in researching the dark matter and dark energy hidden throughout the universe. The first method is gravitational lensing. Dark matter present throughout space bends spacetime, subtly distorting and stretching the appearance of galaxies behind it.
Observing a single galaxy doesn't tell us what it looked like originally, making it difficult to judge exactly how distorted it is. However, the story changes when one observes the shapes of hundreds of millions of galaxies at once and compares them statistically. By analyzing the average direction and degree to which these galaxy images are bent and stretched, we can reverse-engineer the distribution of the dark matter lying between them. Roman’s wide field of view is particularly advantageous for measuring these weak gravitational lensing effects on a large scale.
Reading the History of Cosmic Expansion Through Galaxy Distribution
The second method is mapping the three-dimensional distribution of galaxies in space.
By measuring the spectrum of individual galaxies using the spectrograph mounted on Roman and determining their redshift, astronomers can estimate their distance. This allows for the creation of a massive galaxy map that includes not only 2D positions in the sky but also depth information based on distance.
This map also preserves traces of "Baryon Acoustic Oscillations (BAO)," remnants of the time after the Big Bang when matter and light in the early universe were still combined. By measuring the average intervals at which galaxies are distributed and tracking how those intervals have changed throughout cosmic history, we can determine the history of the universe's expansion.
Ultimately, this serves as a crucial clue to finding out how much dark matter and dark energy exist in the universe and how dark energy has influenced cosmic expansion.
The third method is repeatedly observing the appearance of the universe as it changes over time.
Roman will observe the same portions of the sky at regular intervals. By photographing the same area multiple times, astronomers can discover objects that suddenly appear or disappear within a few days, and capture the variations of starlight that brighten and dim at regular cycles.
Through these time-series observations, astronomers expect to discover over 20,000 new supernovae. Supernovae are vital for understanding cosmic evolution. Because they are so bright, they can be observed over very long distances, and certain types of supernovae are used as "standard candles" for measuring astronomical distances. The very concept of dark energy originated from research that used supernovae to measure distances to far-off galaxies and investigate the history of cosmic expansion.
In particular, these two types of observations—spatial distribution of galaxies and supernovae—have taken on even more intriguing significance in recent cosmology. Recent studies measuring BAO across the universe have raised the possibility that dark energy may be changing over time, with its intensity potentially weakening. On the other hand, there is also the issue that the brightness of supernovae themselves might vary slightly depending on the cosmic epoch. This could also connect to the possibility that dark energy is not constant.
We are at a point where a new debate is beginning regarding the nature of dark energy, one of the greatest mysteries in cosmology. In this context, the large-scale galaxy map and supernova observations that Roman will perform are especially significant.
Another Revolution Brought by Roman: Data
A key innovation of Roman lies not only in its observation equipment but also in how it handles data. Roman is expected to produce approximately 1.4 TB of observational data per day on average. The total volume of data accumulated over five years will reach about 20 PB (petabytes, 10 to the 15th power). This is a scale far more massive than all the data accumulated by Hubble over the past several decades.
Even more importantly, this data will not be exclusively held by a specific research team for a long period; instead, it will be made available to astronomers worldwide as soon as the pre-processing is complete.
However, because the scale of the data is so vast, downloading and analyzing all the material on a personal computer is not realistic. Instead, a method where massive data is stored in a central location and researchers access it via a cloud environment to perform necessary analyses is becoming essential.
As the volume of data exceeds the level that humans can inspect individually, the roles of artificial intelligence and machine learning are growing. Machine learning tools are currently being developed to generate high-precision images similar to actual observations, automatically classify countless galaxies, and identify peculiar celestial objects that change in brightness suddenly.
In the past, citizen science projects involving people from around the world played an important role in classifying vast amounts of astronomical data. Now, the results accumulated from that citizen science are being used as excellent training data to teach AI. An era has begun where AI, having learned from a universe classified by humans, analyzes an even vaster universe quickly and efficiently.
A Wider and More Precise New Universe
The universe revealed by Hubble and James Webb has already left a deep impression on humanity. However, Roman is a telescope of an entirely different dimension. While Hubble and James Webb have dug deeply and precisely into specific, small regions of the universe, Roman peers at a much wider expanse of the universe with equally precise eyes. A single photo captured by Roman will not contain only a few bright stars or one spectacular galaxy. Countless stars and galaxies will be recorded simultaneously, along with the distribution of dark matter filling the spaces between them and the very history of cosmic expansion.
When a new eye on the universe opens, our understanding of the universe itself may also change. The next universe that the Nancy Grace Roman Space Telescope shows us will be different from the one opened by Hubble and James Webb.
Who is the writer, Ji Woong-bae? He loves cats and the universe. After watching 'Galaxy Express 999' as a child, he dreamed of sharing the beauty of the universe. He currently serves as an assistant professor in the Division of Liberal Arts at Sejong University and engages in various science communication activities, including lectures and writing. He is the author of books such as 'On the Uselessness of an Astronomer', 'We Are All Born Astronomers', and 'Strange Questions That Come to Mind When Looking at the Universe', and has translated works such as 'How I Killed Pluto', 'Quantum Life', and 'UFO'.