NASA’s Nancy Grace Roman Space Telescope (or Roman for short), an observatory designed to settle essential questions in the areas of dark energy, exoplanets, and infrared astrophysics, is planned to be launched in 2027. A research group focused on supernovae, in which researcher Lluís Galbany, from the Institute of Space Sciences (ICE-CSIC) and the Institute of Space Studies of Catalonia (IEEC) participates, has been awarded $11 million to develop the tools needed to utilise as cosmological probes the thousands of supernovae (exploding stars) that Roman will discover, and constrain the true nature of the mysterious dark energy that permeates our Universe.
Roman has a primary mirror that is 2.4 metres in diameter - the same size as the Hubble Space Telescope’s primary mirror. But, unlike Hubble, which can only observe a tiny patch of sky, Roman’s field of view is 200 times greater than the Hubble infrared instrument, capturing more of the sky with less observing time. Its primary instrument, the Wide Field Instrument, will measure light from a billion galaxies over the course of the mission lifetime.
With this incredible tool, one of the mission’s key objectives is to determine the expansion history of the universe and to test possible explanations for its apparent acceleration, including dark energy and modifications to general relativity. To achieve this goal, the mission will conduct a generation-defining experiment in time-domain astronomy via a Core Community survey called the High Latitude Time Domain Survey (HLTDS). This survey will enable the discovery and measurements of Type Ia Supernovae (SNe Ia), one of the most mature cosmological probes, when the universe was only 2,000 million years-old (11,500 million years ago), and with unparalleled precision and statistical volume.
Exploring dark energy
Achieving the incredible measurement precision needed to fully use supernovae Ia as cosmological probes, and therefore constrain the true nature of dark energy, requires detailed understanding of every bit of the observatory and how the light from these very distant exploding stars is recorded. This is where the team, including Lluís Galbany (ICE-CSIC, IEEC), David Rubin at University of Hawaiʻi, Dan Scolnic at Duke University, Rebekah Hounsell at NASA Goddard, and Ben Rose at Baylor University, steps in.
They will create a suite of tools for every step of the process to take the raw data from the telescope and turn it into understanding. From improvements to the software that calibrates the data at the level of individual pixels, to pipelines for measuring the brightnesses of objects and how they change over time, they will have the machinery to make the highest-precision measurements possible.
From ICE-CSIC, the supernova research group will be in charge of developing the part of the pipeline responsible for performing the supernova host galaxy linear reconstruction and analysis, and the infrastructure to evaluate the type of the supernova and to characterise their spectroscopic features from Roman’s prism spectra. “The whole collaboration and in particular our supernovae group at ICE-CSIC are very excited about this new challenge. We will be able to observe the furthest type Ia supernovae humans ever have seen, which exploded just 2 billion years after the Big Bang”, said Galbany.
These ultra-precise measurements are not sufficient on their own. Figuring out what they mean requires modelling of how these measurements would differ in varying cosmological scenarios, so the team will also produce model catalogues of supernovae that we would expect to observe in these different conditions.
The observations from Roman will pinpoint these supernovae, but as with many space missions, the science requires adding other kinds of data from ground-based telescopes. The Subaru Telescope on Maunakea (Hawaii, USA) and the Gran Telescopio CANARIAS (GTC) will be used to provide additional monitoring of the supernovae found by Roman, and detailed spectra of the most interesting targets to provide insight into their properties.
“I’m most excited about the possibility of real-time overlap with the big optical imagers (which would increase the cadence and wavelength range of the survey) and highly multiplexed spectroscopy with the new Subaru Prime-Focus Spectrograph. Subaru is pretty unique and is a strong justification for having a large amount of the survey visible from the northern hemisphere,” explained Rubin.
