Exploding stars come in different types, and these different types of supernovae show astronomers different things about the cosmos. There's a scientific appetite to find more of them and boost our knowledge about these exotic events. The Nancy Grace Roman Space Telescope should be able to feed that appetite.

The Roman is due to launch in about two years, and will make its way to its station at the Sun-Earth L2 orbit. After commissioning, it'll begin operations. One of its three primary surveys is the High-Latitude Time-Domain Survey. In that survey, the powerful space telescope will image the same section of sky beyond the Milky Way every five days for two years. The team behind the Roman will stitch these scenes together into one comprehensive movie, a sort of cosmic cinema.

These movies will reveal the presence of Type 1a supernovae. These occur in binary star systems where one star is a white dwarf. White dwarfs have immense gravitational force because they're extremely dense objects. They draw material away from their companion stars, which could be anything from another white dwarf to a giant star. That material builds up on the white dwarf's surface, and when it reaches a critical mass, it triggers a runaway reaction and a supernova explosion.

Type 1a are different from what we can call standard supernovae. Those are core-collapse supernovae, where a massive star collapses into a neutron star or a black hole, or is completely destroyed and leaves behind only a diffuse nebula.

Since Type 1a supernovae explode at a fixed mass, their peak luminosity is known. For that reason, they serve as standard candles, tools astronomers use to accurately gauge the distance to their home galaxies. These accurate distances allow cosmologists to trace the expansion of the Universe.

The Roman's High-Latitude Time-Domain Survey is a critical part of its mission and is aimed at finding Type 1a supernovae and other transients. According to new research and simulations, it should find about 27,000 of them, a shocking number that's about ten times greater than the current number of known Type 1a SN. This comprehensive data set should help cosmologists in their quest to map the expansion of the Universe, a critical part of understanding dark energy.

“Evidence is mounting that dark energy has changed over time, and Roman will help us understand that change by exploring cosmic history in ways other telescopes can’t.” - Dr. Ben Rose - Dept. of Physics and Astronomy, Baylor University

The 27,000 number comes from new research published in The Astrophysical Journal titled "The Hourglass Simulation: A Catalog for the Roman High-latitude Time-domain Core Community Survey." The lead author is Dr. Ben Rose, an assistant Professor of Physics in the Department of Physics and Astronomy at Baylor University.

The Roman will find these explosions by observing light from distant galaxies and looking back in time. The Roman will push that time boundary and allow astronomers to see Type 1a SN further back than ever. Most of the T1a SN observed so far exploded in the last 8 billion years. The Roman's High-Latitude Time-Domain Survey (HLTDS) will uncover thousands that exploded longer than 10 billion years ago, and dozens that exploded even earlier than that. These standard candles will fill a missing gap and are critical evidence of the Universe's expansion in its early age.

This graphic outlines the Nancy Grace Roman Space Telescope's High-Latitude Time Domain Survey. The survey’s main component will cover over 18 square degrees — a region of sky as large as 90 full moons — and will detect supernovae that occurred up to about 8 billion years ago. Smaller areas within the survey can look even further back in time, potentially back to when the universe was around a billion years old. The survey will be split between the northern and southern hemispheres, located in regions of the sky that will be continuously visible to Roman. The bulk of the survey will consist of 30-hour observations every five days for two years in the middle of Roman’s five-year primary mission.

Image Credit: NASA's Goddard Space Flight Center

“Filling these data gaps could also fill in gaps in our understanding of dark energy,” lead author Rose said in a press release. “Evidence is mounting that dark energy has changed over time, and Roman will help us understand that change by exploring cosmic history in ways other telescopes can’t.”

This figure compares the Roman's expected haul of Type 1a SN with the Dark Energy Survey's cosmological sample of the same. "DES has over 1500 SNe in its cosmological sample with very few at z > 1. However, we expect Roman to have nearly 19,000 SN Ia, with the majority above z > 1," the authors write.

Image Credit: Rose et al. 2025. TApJ

Every supernova is essentially a flash in the cosmos, and dissecting the light from the flash reveals what type of event released it. Core collapse SN and T1a SN aren't easy to distinguish at such great distances, but the light changes over time, and can be split apart with spectroscopy to learn more about it. The Roman carries two instruments, and one of them, the Wide-Field Instrument (WFI), allows the telescope to do large-scale spectroscopic surveys.

“By seeing the way an object’s light changes over time and splitting it into spectra — individual colors with patterns that reveal information about the object that emitted the light—we can distinguish between all the different types of flashes Roman will see,” said Rebekah Hounsell, study co-author and assistant research scientist at the University of Maryland-Baltimore County working at NASA’s Goddard Space Flight Center.

The Hourglass Simulation "uses the most up-to-date spectral energy distribution models and rate measurements for 10 extragalactic time-domain sources," the authors explain in their research. "We simulate these models through the design reference Roman Space Telescope survey."

"In total, Hourglass has over 64,000 transient objects, 11,000,000 photometric observations, and 500,000 spectra," the authors write. Hourglass showed that the Roman can expect to find "approximately 21,000 Type Ia supernovae, 40,000 core-collapse supernovae, around 70 superluminous supernovae, ∼35 tidal disruption events, three kilonovae, and possibly pair-instability supernovae."

This impressive data set will drive the study and understanding not only of dark energy, but of many other transient events too. As of 2024, for example, astronomers knew of only about 260 superluminous supernovae (SLSNe). These explosions can be 10p times as luminous as other SN. Only massive stars greater than 40 solar masses are expected to explode as SLSNe, yet astrophysicists aren't certain what causes them. Finding an additional 70 could provide answers to some outstanding questions.

This artist's illustration shows the explosion of SN 2006gy, a superluminous supernova about 238 million light-years away.

Image Credit:

By Credit: NASA/CXC/M.Weiss -

http://chandra.harvard.edu/photo/2007/sn2006gy/more.html#sn2006gy_xray,

Public Domain,

https://commons.wikimedia.org/w/index.php?curid=2080784

The Hourglass Simulation is designed to prepare the science community for the Roman's deluge of data. With its tens of thousands of transients, millions of photometric observations, and hundreds of thousands of spectra, Hourglass will serve as a training tool. "Additionally, Hourglass is a useful data set to train machine learning classification algorithms."

"With the dataset we’ve created, scientists can train machine-learning algorithms to distinguish between different types of objects and sift through Roman’s downpour of data to find them,” Hounsell added in the press release. “While searching for type Ia supernovae, Roman is going to collect a lot of cosmic ‘bycatch’—other phenomena that aren’t useful to some scientists, but will be invaluable to others.”

Among those other phenomena are Tidal Disruption Events (TDE), which occur when a black hole consumes a star. Astronomers know of about 100 of them, and they can reveal the presence of black holes that are otherwise dormant and undetectable. If the Roman can find an additional 35, that will undoubtedly help them answer some of their questions. Not only are their outstanding questions about black holes' masses and spina, but there are also questions about how stars behave in the dense regions near galactic centers.

Kilonovae are another type of cosmic explosion and occur when two neutron stars or a neutron star and a black hole collide. Though they're fainter than SN, Kilonovae release gravitational waves and also produce substantial amounts of heavy elements like gold, platinum, and uranium. There's only one confirmed kilonova explosion, and there are many outstanding questions about them. Astrophysicists want to understand the composition of these elements in their ejecta, and how often they occur and if there are multiple types. If the Roman can find three more, that's a massive increase in the dataset scientists have to work with.

This artist's illustration shows two neutron stars merging, releasing gravitational waves and exploding as a kilonova. There's only one confirmed kilonova, so if the Roman can find three more, that's a massive jump in data.

Image Credit: By University of Warwick/Mark Garlick, CC BY 4.0

Pair-instability supernovae are another exotic type of stellar explosion that scientists want to know more about. Only extremely massive stars between about 130 to 250 solar masses can explode as pair-instability supernovae (PISNe), and they don't leave neutron stars or black holes behind. The progenitor stars is completely destroyed, and only an expanding nebula of gas and dust, including heavy elements synthesized in the explosion, is left behind. Astrophysicists want to know the exact stellar mass of their progenitors and what role metallicity plays.

As it stands now, astrophysicists have only a small handful of candidate PISNe, and if the Roman can find ten of them like the simulation suggests, researchers will have a lot more data to work with.

“I think Roman will make the first confirmed detection of a pair-instability supernova,” Rose said. “They’re incredibly far away and very rare, so you need a telescope that can survey a lot of the sky at a deep exposure level in near-infrared light, and that’s Roman.”

As NASA's next flagship astrophysics mission, the Nancy Grace Roman Space Telescope will make an enormous contribution to our understanding of different types of cosmic explosions. By stitching together its observations into movies that show how different cosmic explosions take place, it will advance our scientific knowledge considerably.

“Whether you want to explore dark energy, dying stars, galactic powerhouses, or probably even entirely new things we’ve never seen before, this survey will be a gold mine,” said Rose.

Each time a new telescope mission is launched, it's after years or even decades of preliminary work, including figuring out what questions need to be asked and what instruments are needed to find the answers. Simulations like the Hourglass simulation are becoming more common, as the astronomy community anticipates and prepares for new data from upcoming missions.

But each mission also produces surprises, and though they're unpredictable, scientists often mention how excited they are to find surprising new things.

“Roman’s going to find a whole bunch of weird and wonderful things out in space, including some we haven’t even thought of yet,” Hounsell said. “We’re definitely expecting the unexpected.”

An illustration the Nancy Grace Roman Space Telescope, set to launch in 2027, if it can survive budget cuts.

Image Credit: NASA/GSFC/SVS

Sadly, the current US administration has taken aim at NASA's budget and announced that the Roman's funding will be cut. Since the current administration has gained a reputation for confusing announcements that are sometimes later rescinded, the mission's future is unclear.

If it is approved and launched, its precious dataset will be a feast for astrophysicists around the world and will help drive a deeper understanding of Nature and some of its most extreme objects and events.

Despite the powerful telescopes that modern astronomers have to work with, the distant reaches of the Solar System are still mysterious. Not much sunlight pierces these regions, and there are strong hints that undiscovered objects lurk there. The objects that astronomers have discovered in these dim reaches are primordial, and their orbits suggest the presence of more undiscovered objects. Piecing it all together is a challenge.

While some objects announce themselves with fiery explosions or streaks of light across the sky, distant Solar System objects don't attract much attention. They reveal themselves in tiny hints; a nearly imperceptible tug on another object, a nearly-invisible and short-lived glimmer of light. Yet these objects have something important to tell us about how our Solar System formed and evolved.

Astronomers have detected hints of a ninth planet in the Solar System's distant reaches. This hypothetical and elusive Planet Nine is held up to explain the puzzling orbital groupings of a family of distant objects called Trans-Neptunian Objects (TNO).

Astronomers working with Japan's Subaru Telescope in Hawaii found evidence of a new distant object in the Solar System. It's a Trans-Neptunian Object, meaning it orbits the Sun at a greater average distance than Neptune, the outermost planet. But it's also a member of an important and puzzling sub-class of objects: Sednoids. It's name is 2023 KQ14, but its nickname is Ammonite, after the fossilized cephalopod.

Sednoids follow more extreme orbits than TNOs. Their orbits are extremely elongated, with high eccentricity, distant perihelia, and large semi-major axes. They're named after the dwarf planet Sedna, and the new discovery is only the fourth Sednoid ever detected.

A new paper in Nature Astronomy presented the discovery. It's titled "Discovery and dynamics of a Sedna-like object with a perihelion of 66 au." The lead author is Ying-Tung Chen from the Academia Sinica Institute of Astronomy and Astrophysics in Taipei, Taiwan.

"Understanding the orbital evolution and physical properties of these unique, distant objects is crucial for comprehending the full history of the Solar System." - Dr. Fumi Yoshida, co-author.

Ammonite was first detected with the Subaru Telescope during observation efforts in March, May, and August 2023. Those observations alone weren't sufficient to confirm the dim object's existence, and follow-up observations in July 2024 with the Canada-France-Hawaii Telescope, as well as a search through archived data from other observatories, provided confirmation. Overall, the researchers tracked Ammonite's orbit for 19 years.

Ammonite was found as part of the FOSSIL (Formation of the Outer Solar System: An Icy Legacy) observing program. It uses the Subaru Telescope's powerful HyperSuprimeCam to measure the populations and sub-populations of the objects that populate the outer Solar System. The FOSSIL team used computer numerical simulations to determine that Ammonite has followed a stable orbit for at least 4.5 billion years, dating all the way back to the Solar System's earliest times. Ammonite's orbit is currently different from the other Sednoids, but the simulations show that there orbits were all similar about 4.2 billion years ago.

There's an odd gap in distant Solar System objects when it comes to their perihelion distances and Ammonite sits in that gap. "The orbit of Ammonite does not align with those of the other Sedna-like objects and fills the previously unexplained ‘q-gap’ in the observed distribution of distant Solar System objects," the authors explain in their paper.

This figure is divided into two panels divided by a vertical black line, and shows the orbital data for outer Solar System objects. The left side shows the semi-major axis versus perihelion distribution, with the red vertical dashed line representing the approximate region where galactic tides and passing stars can perturb the orbits of TNOs. The horizontal black lines show the upper boundary of chaotic diffusion and gravitational scattering by Neptune. The named objects all have large perihelia, and it clearly shows hos Ammonite is different from the others. It's in the region that currently lacks any other detections. The right side shows how Ammonite falls outside the proposed clustering of objects with large perihelia.

Image Credit: Chen et al. 2025. NatAstr. https://doi.org/10.1038/s41550-025-02595-7

Dr. Yukun Huang of the NAOJ is a co-author of the paper who conducted simulations of Ammonite's orbit. "The fact that 2023 KQ14’s current orbit does not align with those of the other three sednoids lowers the likelihood of the Planet Nine hypothesis," Huang said in a press release. "It is possible that a planet once existed in the Solar System but was later ejected, causing the unusual orbits we see today."

Neptune is the only known massive object near the outer Solar System that could have shaped the orbits of the TNOs and Sednoids. But according to study co-author Dr. Fumi Yoshida, Ammonite is beyond its reach.

“2023 KQ14 was found in a region far away where Neptune’s gravity has little influence. The presence of objects with elongated orbits and large perihelion distances in this area implies that something extraordinary occurred during the ancient era when 2023 KQ14 formed," Yoshida said. "Understanding the orbital evolution and physical properties of these unique, distant objects is crucial for comprehending the full history of the Solar System. At present, the Subaru Telescope is among the few telescopes on Earth capable of making such discoveries. I would be happy if the FOSSIL team could make many more discoveries like this one and help draw a complete picture of the history of the Solar System.”

Ammonite's orbit is now different from the other Sednoids, and that fact needs an explanation. It's evidence that there's more complexity and diversity among distant Solar System objects. Astronomers have long wondered if our Solar System hosts a 'Planet Nine' that has shepherded the orbits of these distant objects. If there is, then Ammonite's discovery places more constraints on its orbit, and where it may be hiding. It effectively reduces the number of hiding spots for this hypothetical planet.

An artist's illustration of the mysterious, elusive, hypothesized Planet Nine.

Image Credit: NASA

"Sedna-like objects with large semi-major axes (a > 200 au) and large perihelia (q > 60 au) appear to evolve in stable orbits that have remained largely unchanged and not altered by the gravity of Neptune since the formation of the Solar System," the researchers explain in their paper. "No viable transfer mechanisms to raise their perihelia exist with the current configuration of planets. Their stability suggests that an external gravitational influence beyond those of the currently known Solar System planets is required to form their orbits."

This figure shows the orbits of the four Sednoids, with Neptune's orbit around the Sun shown for comparison. "Ammonite’s longitude of perihelion is in the opposite direction of the other Sedna-like objects," the authors explain. "Its high perihelion suggests the potential for long-term orbital stability," and it's valuable for testing the hypothesized clustering of Sednoids and the hypothetical Planet Nine.

Image Credit: Chen et al. 2025. NatAstr. https://doi.org/10.1038/s41550-025-02595-7

Astronomers have proposed many sources for this external gravitational influence, including interactions with a rogue planet or star, ancient stellar interactions from when the Sun was still in its natal cluster, and the capture of objects from other lower-mass stars in the Solar System's early times. But the explanation that gets the most attention is interactions with a hypothetical planet, Planet Nine.

While this study neither confirms nor disputes the existence of Planet Nine, it does place further constraints on its orbit. In fact, each time another Sednoid is discovered, it constrains Planet Nine. Astronomers now know of four of them, but they don't know how many may still be hiding out there, potentially shepherded by the elusive, hypothetical, Planet Nine.

If Planet Nine exists, it has a huge area to hide in. Some astronomers who have studied its potential existence think it could be the fifth largest planet in the Solar System. It would be so far away that it would be extremely dim. However, we may be on the cusp of detecting it, if it exists.

The Vera Rubin Observatory recently saw first light and will begin its decade-long Legacy Survey of Space and Time (LSST). The LSST will find transient events and objects in the Solar System like no other telescope before it. It's purpose-built to find hard to detect objects, and not even an elusive object like Planet Nine may be able to hide from it.