[Science Scope] Roman's Quest to Uncover the Universe's Secrets... A New Opportunity for Korean Astronomy

Dark Energy and Exoplanet Exploration... Observing an Area 200 Times Wider Than Hubble
Joint Observations with KMTNet Expected... Korea-Led KLST Plan

Editor's Note"Science Scope" is a feature that takes an in-depth look at specific scientific and technological phenomena and analyzes their significance and future prospects.

Technicians inspect the assembly of the Nancy Grace Roman Space Telescope in a clean room at NASA's Goddard Space Flight Center. The telescope will survey wide areas of space at high resolution to study the nature of dark energy and exoplanets. Courtesy of NASA.

Why is the universe expanding at an accelerating rate? How many planets are wandering alone through the Milky Way, unattached to any star? To answer these two questions that astronomers have long been unable to solve, NASA's Nancy Grace Roman Space Telescope has headed into space. Launched on August 30, the Roman Space Telescope is currently undergoing final equipment checks ahead of the start of its full-scale scientific observations.

Roman has a primary mirror with the same 2.4-meter diameter as the Hubble Space Telescope, but its near-infrared field of view is about 200 times wider. It is set to observe countless galaxies and supernovae and search for signs of exoplanets in minute changes in starlight.

Roman's arrival also presents an opportunity for the Korean astronomical community. This is because researchers can link Roman's observations with data accumulated by the Korea Microlensing Telescope Network (KMTNet), operated by the Korea Astronomy and Space Science Institute, and draw on domestic researchers' experience in international collaborative research. It is also connected to plans for the Korea-led Large Spectroscopic Telescope (KLST).

In a written interview with The Asia Business Daily, Park Byeong-gon, a principal researcher at the Korea Astronomy and Space Science Institute, said, "The Roman Space Telescope is expected to usher in a new era through groundbreaking observations in dark energy and exoplanet research. If KMTNet in Korea can collaborate with the Roman Space Telescope, the resulting synergy could lead to even greater achievements."

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Roman Takes a Wide View; James Webb Looks Deeper

Roman's most distinctive feature is its wide-field observing capability. Because it can observe many celestial objects at once, it is well suited to searching for phenomena that occur infrequently or are difficult to predict. Supernova explosions and gravitational microlensing are two prominent examples.

It is difficult to predict when and where a supernova will explode. Gravitational microlensing is also a rare phenomenon that occurs when another celestial object happens to pass directly between a distant star and the observer. Roman will repeatedly observe a wide area of the sky to find such phenomena. It will also investigate the positions and distances of galaxies to trace the universe's three-dimensional structure and evolution.

This is also where Roman differs from the James Webb Space Telescope (JWST). With a 6.5-meter primary mirror, James Webb excels at closely analyzing specific celestial objects, such as the atmospheric composition of exoplanets or faint galaxies in the early universe. Roman, by contrast, is better suited to finding new celestial objects and phenomena on a large scale across a wide area. The two telescopes are complementary.

Does Dark Energy Really Stay Constant?

One of Roman's key missions is to uncover the nature of dark energy, which is believed to be driving the universe's accelerated expansion. In the late 1990s, astronomers discovered, while observing distant stellar explosions, that the universe's expansion was actually speeding up.

They used what are known as Type Ia supernovae. These occur when a stellar remnant called a white dwarf explodes. The characteristics of the brightness produced by the explosion can be used to measure distance. This made it possible to determine the universe's expansion rate.

An artist's impression of NASA's Nancy Grace Roman Space Telescope observing the universe. With its wide field of view, the telescope will observe countless galaxies and stars to study the nature of dark energy, the history of the universe's expansion, exoplanets, and more. Image courtesy of NASA.

Scientists introduced the concept of "dark energy" to explain the accelerated expansion. The most widely accepted cosmological model today assumes that dark energy does not change over time, but this has not been confirmed.

Roman plans to trace the history of the universe's expansion by observing more supernovae and galaxies. It will also analyze weak gravitational lensing, a phenomenon in which the light from distant galaxies is subtly bent by the gravity of matter. This will help researchers understand the distribution of dark matter and how cosmic structures grow.

Recent research by the Dark Energy Spectroscopic Instrument (DESI), which involves the U.S. Department of Energy and other organizations, has produced preliminary results suggesting that dark energy may change over time. While these are not yet conclusive, Roman's observations are expected to help independently verify the findings.

Principal Researcher Park said, "The Roman Space Telescope will not only measure the universe's accelerated expansion with greater precision, but may also determine whether Einstein's cosmological constant, which describes the expansion of the universe, is a physical quantity that changes over time. This could lead to revisions to Einstein's theory of gravity."

However, Roman will not be able to uncover the true nature of dark energy on its own. More rigorous verification will require combining its data with data from the European Space Agency's Euclid space telescope, the Planck satellite, the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), DESI, and other projects.

Roman's Search for Rogue Planets... The Role of Korea's KMTNet

Another major mission for Roman is the search for exoplanets. In particular, it plans to use gravitational microlensing to find planets that have been difficult to detect with previous observations.

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Gravitational microlensing is a phenomenon in which the gravity of a foreground object temporarily brightens the light from a distant star. Analyzing changes in brightness can reveal the presence of exoplanets. The method is well suited to finding planets far from their host stars, as well as "rogue planets" that drift through space without orbiting any particular star.

Roman is expected to discover about 1,400 exoplanets by observing gravitational microlensing toward the center of the Milky Way. It will also search for exoplanets using the transit method, which detects the dimming of starlight when a planet passes in front of its star.

KMTNet, operated by the Korea Astronomy and Space Science Institute, consists of three telescopes, each with a 1.6-meter diameter, installed in Chile, South Africa, and Australia. By placing telescopes at different longitudes, the network continuously observes the night sky.

In operation since 2015, KMTNet has accumulated substantial data from its search for exoplanets using gravitational microlensing. Roman can observe stars in the central regions of the galaxy that are obscured by dust using infrared light, while KMTNet has the advantage of making long-term observations from the ground in visible light.

If the two facilities observe the same gravitational microlensing event, they can also use the parallax effect caused by their difference in position. Because Roman observes from near the second Lagrange point (L2), about 1.5 million kilometers from Earth, it and KMTNet will view the same event from different directions.

Principal Researcher Park said, "When KMTNet, a ground-based telescope network, and the Roman Space Telescope in orbit around L2 observe the same microlensing event, a parallax effect arises from the difference in their viewing directions. Using this parallax, we can measure the mass of an exoplanet more precisely."

However, there is also a limitation: Roman mainly observes the central regions of the galaxy, while KMTNet focuses on areas somewhat farther from the center, restricting the number of targets they can observe in common.

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Korea Prepares for the Era After Roman... The Significance of the KLST Plan

Roman's arrival raises the question of what role the Korean astronomical community will play in major international observing projects. When a space telescope discovers a celestial object, a large ground-based telescope analyzes its light at different wavelengths to determine its distance and physical properties.

Research groups at the Korea Astronomy and Space Science Institute are already involved in research with the Rubin Observatory's LSST and DESI. Their experience in international collaborative research could be used to combine Roman's observations with data from other surveys.

The next step in these plans is the Korea Large Spectroscopic Telescope (KLST), a large spectroscopic telescope project led by Korea. The Korea Astronomy and Space Science Institute is planning a project to build two telescopes, each with a diameter of about 6.5 meters, in the Southern Hemisphere, enabling simultaneous spectroscopic observations of up to 13,000 celestial objects.

Park Byeonggon, principal research scientist at the Korea Astronomy and Space Science Institute. Provided by KASI.

If the KLST becomes a reality, it could contribute to research on dark energy and the large-scale structure of the universe by precisely analyzing light from celestial objects discovered by Roman or the Rubin Observatory. It would also open up the possibility of Korea building its own observing infrastructure and leading research.

However, construction of the KLST has not yet been confirmed. Challenges remain, including securing a budget, establishing an international cooperation framework, and recruiting staff to operate the project. Joint observations with Roman are also a research direction that requires further consideration.

Principal Researcher Park said, "We expect Korean astronomers participating in the LSST and DESI surveys to collaborate actively with the Roman Space Telescope research group. Furthermore, if the Korea-led KLST project, a large spectroscopic space survey telescope currently in the planning stage, becomes a reality, Korea could emerge as an international leader in research in this field."

This content was produced with the assistance of AI translation services.