Team preps to study dark energy via exploding stars with NASA's Roman

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Frame sequence of single Roman detector. The video sparkles with synthetic supernovae from observations of the OpenUniverse simulated universe taken every five days (similar to the expected cadence of Roman’s High-Latitude Time-Domain Survey, which OpenUniverse simulates in its entirety). To highlight the dynamic physics happening and for visibility at this scale, the true brightness of each transient event has been magnified by a factor of 10,000 and no background light has been added to the simulated images. NASA’s Goddard Space Flight Center and M. Troxel

The universe is ballooning outward at an ever-faster clip under the power of an unknown force dubbed dark energy. One of the major goals for NASA's upcoming Nancy Grace Roman Space Telescope is to help astronomers gather clues to the mystery. One team is setting the stage now to help astronomers prepare for this exciting science.

"Roman will scan the cosmos a thousand times faster than NASA's Hubble Space Telescope can while offering Hubble-like image quality," said Rebekah Hounsell, an assistant research scientist at the University of Maryland-Baltimore county working at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and a co-principal investigator of the Supernova Cosmology Project Infrastructure Team preparing for the mission's High-Latitude Time-Domain Survey. "We're going to have an overwhelming amount of data, and we want to make it so scientists can use it from day one."

Roman will repeatedly look at wide, deep regions of the sky in near-infrared light, opening up a whole new view of the universe and revealing all sorts of things going bump in the night. That includes stars being shredded as they pass too close to a black hole, intense emissions from galaxy centers, and a variety of stellar explosions called supernovae.

Cosmic radar guns

Scientists estimate around half a dozen stars explode somewhere in the observable universe every minute. On average, one of them will be a special variety called type Ia that can help astronomers measure the universe.

This data sonification transforms a vast simulation of a cosmic survey from NASA's upcoming Nancy Grace Roman Space Telescope into a symphony of stellar explosions. Each supernova's brightness controls its volume, while its color sets its pitch––redder, more distant supernovae correspond to deep, low tones while bluer, nearer ones correspond to higher frequencies. The sound in stereo mirrors their locations in the sky. The result sounds like celestial wind chimes, offering a way to "listen" to cosmic fireworks. Credit: NASA's Goddard Space Flight Center, M. Troxel, SYSTEM Sounds (M. Russo, A. Santaguida)

These explosions peak at a similar intrinsic brightness, allowing scientists to find their distances simply by measuring how bright they appear.

Scientists can also study the light of these supernovae to find out how quickly they are moving away from us. By comparing how fast they're receding at different distances, scientists will trace cosmic expansion over time.

Using dozens of type Ia supernovae, scientists discovered that the universe's expansion is accelerating. Roman will find tens of thousands, including very distant ones, offering more clues about the nature of dark energy and how it may have changed throughout the history of the universe.

"Roman's near-infrared view will help us peer farther because more distant light is stretched, or reddened, as it travels across expanding space," said Benjamin Rose, an assistant professor at Baylor University in Waco, Texas, and a co-principal investigator of the infrastructure team. "And opening a bigger window, so to speak, will help us get a better understanding of these objects as a whole," which would allow scientists to learn more about dark energy. That could include discovering new physics, or figuring out the universe's fate.

This data sonification transforms a vast simulation of a cosmic survey from NASA's upcoming Nancy Grace Roman Space Telescope into a symphony of stellar explosions. Each supernova's brightness controls its volume, while its color sets its pitch––redder, more distant supernovae correspond to deep, low tones while bluer, nearer ones correspond to higher frequencies. The sound in stereo mirrors their locations in the sky. The result sounds like celestial wind chimes, offering a way to "listen" to cosmic fireworks. Credit: NASA's Goddard Space Flight Center, M. Troxel, SYSTEM Sounds (M. Russo, A. Santaguida)

The people's telescope

Members of the planning team have been part of the community process to seek input from scientists worldwide on how the survey should be designed and how the analysis pipeline should work. Gathering public input in this way is unusual for a space telescope, but it's essential for Roman because each large, deep observation will enable a wealth of science in addition to fulfilling the survey's main goal of probing dark energy.

Rather than requiring that many individual scientists submit proposals to reserve their own slice of space telescope time, Roman's major surveys will be coordinated openly, and all the data will become public right away.

"Instead of a single team pursuing one science goal, everyone will be able to comb through Roman's data for a wide variety of purposes," Rose said. "Everyone will get to play right away."

This video sparkles with synthetic supernovae from the OpenUniverse project, which simulates observations from NASA's upcoming Nancy Grace Roman Space Telescope. More than a million exploding stars flare into visibility and then slowly fade away. The true brightness of each transient event has been magnified by a factor of 10,000 for visibility, and no background light has been added to the simulated images. The pattern of squares shows Roman's full field of view. Credit: NASA's Goddard Space Flight Center and M. Troxel

This is a drill

NASA plans to announce the survey design for Roman's three core surveys, including the High-Latitude Time-Domain Survey, this spring. Then the planning team will simulate it in its entirety.

"It's kind of like a recipe," Hounsell said. "You put in your observing strategy — how many days, which filters — and add in 'spices' like uncertainties, calibration effects, and the things we don't know so well about the instrument or supernovae themselves that would affect our results. We can inject supernovae into the synthetic images and develop the tools we'll need to analyze and evaluate the data."

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Scientists will continue using the synthetic data even after Roman begins observing, tweaking all aspects of the simulation and correcting unknowns to see which resulting images best match real observations. Scientists can then fine-tune our understanding of the universe's underlying physics.

This animation shows a possible tiling pattern of part of NASA's Nancy Grace Roman Space Telescope's High Latitude Time-Domain Survey. The observing program, which is being designed by a community process, is expected to have two components: wide (covering 18 square degrees, a region of sky as large as about 90 full moons) and deep (covering about 5.5 square degrees, about as large as 25 full moons). This animation shows the deeper portion, which would peer back to when the universe was about 500 million years old, less than 4 percent of its current age of 13.8 billion years. Credit: NASA's Goddard Space Flight Center

"We assume that all supernovae are the same regardless of when they occurred in the history of the universe, but that might not be the case," Hounsell said. "We're going to look further back in time than we've ever done with type Ia supernovae, and we're not completely sure if the physics we understand now will hold up."

There are reasons to suspect they may not. The very first stars were made almost exclusively of hydrogen and helium, compared to stars today which contain several dozen elements. Those ancient stars also lived in very different environments than stars today. Galaxies were growing and merging, and stars were forming at a furious pace before things began calming down between about 8 and 10 billion years ago.

"Roman will very dramatically add to our understanding of this cosmic era," Rose said. "We'll learn more about cosmic evolution and dark energy, and thanks to Roman's large deep view, we'll get to do much more science too with the same data. Our work will help everyone hit the ground running after Roman launches."

Provided by NASA's Goddard Space Flight Center