Science Themes

The Nancy Grace Roman Space Telescope is designed to investigate three key science themes: dark energy, dark matter, and exoplanets. In addition, the mission will enable incredible discoveries in general astrophysics and planetary science. The science program will be addressed using two instruments, focused observing surveys, General Astrophysics observing programs, and Archival programs.

Dark Energy

The Roman Space Telescope will measure the equation of state of dark energy and its time evolution, helping to determine whether it is a cosmological constant. The High Latitude Wide-Area Survey (HLWAS) will enable weak lensing shape and photometric redshift measurements of hundreds of millions of galaxies, which will yield precise estimates of distances and matter clustering through measurements of cosmic shear, galaxy-galaxy lensing, and the abundance and mass profiles of galaxy clusters. Spectroscopic measurements over the same area will enable the determination of millions of redshifts for galaxies between z=1 and 3, thus allowing a measurement the growth of structure via redshift-space distortions, and the constraint of the scale of baryon acoustic oscillations to 0.3%. At the same time, the High Latitude Time Domain Survey (HLTDS) will enable the discovery and measurement of precise distances to thousands of Type Ia supernovae up to redshift z=2. 

Both the High Latitude Wide Area Survey and the High Latitude Time Domain Survey will have unique control of measurement errors and astrophysical systematics. Of existing and planned observatories, Roman will be the most powerful supernova, weak lensing, and redshift 1 to 2 spectroscopic facility per unit time, and is expected to yield the densest large-scale map of structure at redshifts of 1 to 2.

Supporting Surveys: High Latitude Wide Area Survey, High Latitude Time Domain Survey

Read more about Dark Energy.

Dark Matter

Roman will be used to investigate dark matter in a number of ways, including the study of weak gravitational lensing effects. Weak lensing tracks how the shape of distant galaxies is warped by small clumps of dark matter.

Additionally, the large footprint of the Roman Wide Field Instrument (WFI) will allow an inventory of both normal matter and dark matter in hundreds of millions of galaxies. Such observations will be used to understand how dark matter has driven the formation and evolution of stars and galaxies as a function of cosmic time. If galaxy formation is observed very early in cosmic history, it could signal that dark matter is made of heavy, sluggish particles which tend to clump together fast. On the other hand, if the dark matter clumps grow more slowly and the large-scale structure is established over a longer time scale, it would indicate that dark matter is made up of lighter, faster-moving particles.

Roman’s observations will help reconstructing the history of galaxies and clusters formation under the influence of dark matter, which, in turn, will help scientists narrow down candidates for dark matter particles, pointing the way for direct detection in experiments on Earth.

Supporting Surveys: High Latitude Wide Area Survey, General Astrophysics Program

Read more about Dark Matter and Astrophysics.

Exoplanets

Roman will use time-series microlensing imaging observations of Milky Way Bulge stars to determine the distribution of exoplanets down to sub-Earth masses in a wide range of orbital radii, including the habitable zone, the outer regions of planetary systems, and free-floating planets.

The coronographic instrument on Roman will provide a crucial technology demonstration for possible future missions aimed at detecting signs of life in the atmospheres of Earth-like exoplanets. It will also be capable of directly imaging planets similar to those in our Solar System, measuring for the first time the photometric properties of the 'mini-Neptune' or 'super-Earth' planets — objects that Kepler has shown to be the most common planets in our galaxy, but with no analogy in our own solar system.

Supporting Surveys: Galactic Bulge Time Domain Survey, Coronagraph Instrument

Read more about Exoplanets.

General Astrophysics and Planetary Science

Roman will be the first telescope to combine excellent, space-based image quality with survey power. Roman’s 300 Megapixel WFI camera will have ~200 times the field of view of Hubble at a similar sensitivity and resolution. The data collected for the Roman core community surveys will form a treasure trove for archival studies in many areas of general astrophysics. Single images from WFI will yield survey-sized datasets, covering the equivalent of 200 IR pointings with the Hubble and James Webb space telescopes.

For example, data collected under the High-Latitude Wide Area Survey as conceptualized in the Roman's design reference mission, would enable a plethora of general astrophysics science, including but not limited to: mapping the formation of cosmic structure in the first billion years after the big bang via the detection and characterization of over 10,000 galaxies at z > 8; finding over 2,000 QSOs at z > 7; quantifying the distribution of dark matter on intermediate and large scales through lensing in clusters and in the field; identifying the most extreme star-forming galaxies and shock-dominated systems at 1 < z < 2; carrying out a complete census of star-forming galaxies and the faint end of the QSO luminosity function at z ~ 2, including their contribution to the ionizing radiation; determining the kinematics of stellar streams in the Local Group through proper motions; discovering and characterizing small bodies in our solar system such as Kuiper Belt objects, including asteroids and comets.

In addition, a significant fraction of mission time will be set aside for General Astrophysics observing programs with the Wide Field Instrument. This will allow the use of the broad range of Roman's capabilities, namely wide-field imaging and slitless spectroscopy, for many additional studies. Examples include studying young clusters and embedded star-forming regions within the Milky Way galaxy; reaching the very faint end of the stellar luminosity function via very deep observations of Local Group galaxies; mapping the core of the Virgo cluster; and follow-up studies of systems found through WFI high latitude imaging and spectroscopic survey observations (high-redshift QSOs and galaxies, galaxy clusters). A Participating Scientist Program with the Coronagraph Instrument is expected upon successful completion of the technology demonstration.

Appendix D of the final report of the WFIRST-AFTA Science Definition Team includes one-page summaries of many other possible General Astrophysics observing and archival programs, covering areas of science ranging from the Solar System to cosmology.

Supporting Programs: Coronograph Instrument Program, General Astrophysics and Archival Research Programs

Read more about Astrophysics and Synergies with the Rubin Telescope.