The survey's primary target is type Ia supernovae, whose intrinsic brightness allows precise distance measurements. Roman aims to find tens of thousands of these explosions at record distances. Measuring their apparent motion will let scientists trace how cosmic expansion has changed over billions of years, revealing insights into dark matter and dark energy.
Roman will detect supernovae from as early as 3 billion years after the big bang, extending expansion measurements to 11 billion years in the past. Ground-based observatories like the Vera C. Rubin Observatory can only probe the last 5 billion years due to atmospheric limits. Recent results hint that dark energy's strength may be changing; Roman's deep surveys will critically test this.
The High-Latitude Time-Domain Survey will spend 180 observing days over five years, with most observations during a central two-year window, revisiting fields every five days. Early baseline imaging will enable change detection through image subtraction. A long-term component will revisit fields every 120 days to catch slow-evolving, distant events, benefiting from time dilation.
This extended monitoring will capture rare, powerful transients like tidal disruption events and hypothetical pair-instability supernovae. The survey will have two imaging tiers: a wide tier covering over 18 square degrees for the past 7 billion years, and a deep tier spanning 6.5 square degrees to reach 10 billion years back. Observations will be split between northern and southern sky regions, with Roman performing spectroscopy in the south and Subaru Observatory covering the north.
Together with Roman's High-Latitude Wide-Area Survey and Galactic Bulge Time-Domain Survey, this effort will produce an unprecedented map of the universe.
Related Links
Nancy Grace Roman Space Telescope
Stellar Chemistry, The Universe And All Within It
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