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Roman Space Telescope – The Resolution of Hubble with a 100 Times Larger Field of View
This image, called the eXtreme Deep Field, or XDF, was assembled by combining 10 years of NASA Hubble Space Telescope photographs taken of a patch of sky at the center of the original Hubble Ultra Deep Field. The Hubble Ultra Deep Field is an image of a small area of space in the constellation Fornax, created using Hubble Space Telescope data from 2003 and 2004. By collecting faint light over many hours of observation, it revealed thousands of galaxies, both nearby and very distant, making it the deepest image of the universe ever taken at that time. This full-color XDF image is even more sensitive and contains about 5,500 galaxies, the faintest being one ten-billionth the brightness of what the human eye can see. Magnificent spiral galaxies similar in shape to our Milky Way Galaxy appear in this image, as do the large, fuzzy red galaxies where the formation of new stars has ceased. These red galaxies are the remnants of dramatic collisions between galaxies and are in their declining years. Peppered across the field are tiny, faint, more distant galaxies that were like the seedlings from which today's magnificent galaxies grew. The history of galaxies -- from soon after the first galaxies were born to the great galaxies of today -- is laid out in this one remarkable image. The universe is 13.7 billion years old, and the XDF reveals galaxies that span back 13.2 billion years in time. Most of the galaxies in the XDF are seen when they were young, small, and growing, often violently as they collided and merged together. The early universe was a time of dramatic birth for galaxies containing brilliant blue stars extraordinarily brighter than our sun. The light from those past events is just arriving at Earth now, and so the XDF is a "time tunnel into the distant past." The youngest galaxy found in the XDF existed just 450 million years after the universe's birth in the big bang. (Image Credit NASA; ESA; G. Illingworth, D. Magee, and P. Oesch, University of California, Santa Cruz; R. Bouwens, Leiden University; and the HUDF09 Team)
Roman Space Telescope – The Resolution of Hubble with a 100 Times Larger Field of View
In 1995, the Hubble Space Telescope stared at a blank patch of the sky for 10 straight days. The resulting Deep Field image captured thousands of previously unseen, distant galaxies. Similar observations have followed since then, including the longest and deepest exposures, the Hubble Ultra Deep Field and the eXtreme Deep Field. Now, astronomers are looking ahead to the future, and the possibilities enabled by NASA’s upcoming Nancy Grace Roman Space Telescope, scheduled for launch in 2025.
The Roman Space Telescope will be able to photograph an area of sky 100 times larger than Hubble with the same exquisite sharpness. As a result, a Roman Ultra Deep Field would collect millions of galaxies, including hundreds that date back to just a few hundred million years after the big bang. Such an observation would fuel new investigations into multiple science areas, from the structure and evolution of the universe to star formation over cosmic time.
One of the Hubble Space Telescope’s most iconic images is the Hubble Ultra Deep Field, which unveiled myriad galaxies across the universe, stretching back to within a few hundred million years of the Big Bang. Hubble peered at a single patch of seemingly empty sky for hundreds of hours beginning in September 2003, and astronomers unveiled the galaxy tapestry in 2004, with more observations in subsequent years.
NASA’s upcoming Nancy Grace Roman Space Telescope will be able to photograph an area of the sky at least 100 times larger than Hubble with the same crisp sharpness. Among the many observations that will be enabled by this wide view of the cosmos, astronomers are considering the possibility and scientific potential of a Roman Space Telescope “ultra-deep field.” Such an observation could reveal new insights into subjects ranging from star formation during the universe’s youth to the way galaxies cluster together in space.
Roman will enable new science in all areas of astrophysics, from the solar system to the edge of the observable universe. Much of Roman’s observing time will be dedicated to surveys over wide swaths of the sky. However, some observing time will also be available for the general astronomical community to request other projects. A Roman ultra deep field could greatly benefit the scientific community, say astronomers.
“As a community science concept, there could be exciting science returns from ultra-deep field observations by Roman. We would like to engage the astronomical community to think about ways in which they could take advantage of Roman’s capabilities,” said Anton Koekemoer of the Space Telescope Science Institute in Baltimore, Maryland.
As an example, a Roman ultra-deep field could be similar to the Hubble Ultra Deep Field – looking in a single direction for a few hundred hours to build up an extremely detailed image of very faint, distant objects. Yet while Hubble snagged thousands of galaxies this way, Roman would collect millions. As a result, it would enable new science and vastly improve our understanding of the universe.
Structure and History of the Universe
Perhaps most exciting is the possibility of studying the very early universe, which corresponds to the most distant galaxies. Those galaxies are also the rarest: for example, only a handful are seen in the Hubble Ultra Deep Field.
Thanks to Roman’s wide field of view and near-infrared data of similar quality to Hubble’s, it could discover many hundreds, or possibly thousands, of these youngest, most distant galaxies, interspersed among the millions of other galaxies. That would let astronomers measure how they group together in space as well as their ages and how their stars have formed.
“Roman would also yield powerful synergies with current and future telescopes on the ground and in space, including NASA’s James Webb Space Telescope and others,” said Koekemoer.
Moving forward in cosmic time, Roman would pick up additional galaxies that existed about 800 million to 1 billion years after the big bang. At that time, galaxies were just beginning to group together into clusters under the influence of dark matter. While researchers have simulated this process of forming large-scale structures, a Roman ultra-deep field would provide real world examples to test those simulations.
Star Formation Over Cosmic Time
The early universe also experienced a firestorm of star formation. Stars were being born at rates hundreds of times faster than what we see today. In particular, astronomers are eager to study “cosmic dawn” and “cosmic noon,” which together cover a time 500 million to 3 billion years after the big bang when most star formation was happening, as well as when supermassive black holes were most active.
“Because Roman’s field of view is so large, it will be game changing. We would be able to sample not just one environment in a narrow field of view, but instead a variety of environments captured by Roman’s wide-eyed view. This will give us a better sense of where and when star formation was happening,” explained Sangeeta Malhotra of NASA Goddard Space Flight Center in Greenbelt, Maryland. Malhotra is a co-investigator on the Roman science investigation teams working on cosmic dawn, and has led programs that do deep spectroscopy with Hubble, to learn about distant, young galaxies.
Astronomers are eager to measure star formation rates in this distant epoch, which could influence a variety of factors such as the amount of heavy elements observed. Rates of star formation might depend on whether or not a galaxy lies within a large cluster. Roman will be capable of taking faint spectra that will show distinct “fingerprints” of these elements, and give accurate distances (called redshifts) of galaxies.
“Population experts might ask, what differences are there between people who live in big cities, versus those in suburbia, or rural areas? Similarly, as astronomers we can ask, do the most active star forming galaxies live in very clustered regions, or just at the edges of clusters, or do they live in isolation?” Malhotra said.
Big Data and Machine Learning
One of the greatest challenges of the Roman mission will be learning how to analyze the abundance of scientific information in the public datasets that it will produce. In a sense, Roman will create new opportunities not only in terms of sky coverage, but also in data mining.
A Roman ultra-deep field would contain information on millions of galaxies – far too many to be studied by researchers one at a time. Machine learning—a form of artificial intelligence—will be needed to process the massive database. While this is a challenge, it also offers an opportunity. “You could explore completely new questions that you couldn’t previously address,” stated Koekemoer.
“The discovery potential enabled by the huge datasets from the Roman mission could lead to breakthroughs in our understanding of the universe, beyond what we might currently envision,” Koekemoer added. “That could be Roman’s lasting legacy for the scientific community: not only in answering the science questions we think we can address, but also new questions that we have yet to think of.”
Last year, NASA named its next-generation Wide Field Infrared Survey Telescope (WFIRST), in honor of Nancy Grace Roman, NASA’s first chief astronomer, who paved the way for space telescopes focused on the broader universe.
The Nancy Grace Roman Space Telescope – or Roman Space Telescope, for short – is set to launch in 2025. It will investigate long-standing astronomical mysteries, such as the force behind the universe’s expansion, and search for distant planets beyond our solar system.
Considered the “mother” of NASA’s Hubble Space Telescope, which launched 30 years ago, Nancy Grace Roman tirelessly advocated for new tools that would allow scientists to study the broader universe from space. She left behind a tremendous legacy in the scientific community when she died in 2018.
“It is because of Nancy Grace Roman’s leadership and vision that NASA became a pioneer in astrophysics and launched Hubble, the world’s most powerful and productive space telescope,” said NASA Administrator Jim Bridenstine. “I can think of no better name for WFIRST, which will be the successor to NASA’s Hubble and Webb Telescopes.”
Who Was Nancy Grace Roman?
Born on May 16, 1925, in Nashville, Tennessee, Roman consistently persevered in the face of challenges that plagued many women of her generation interested in science. By seventh grade, she knew she wanted to be an astronomer. Despite being discouraged about going into science – the head of Swarthmore College’s physics department told her he usually dissuaded girls from majoring in physics, but that she “might make it” – Roman earned a bachelor’s degree in astronomy from Swarthmore in 1946 and a doctorate from the University of Chicago in 1949.
She remained at Chicago for six years and made discoveries about the compositions of stars that had implications for the evolution of our Milky Way galaxy. Knowing that her chances of achieving tenure at a university as a woman were slim at that time, she took a position at the U.S. Naval Research Laboratory and made strides in researching cosmic questions through radio waves.
Roman came to NASA in 1959, just six months after the agency had been established. At that time, she served as the chief of astronomy and relativity in the Office of Space Science, managing astronomy-related programs and grants.
“I knew that taking on this responsibility would mean that I could no longer do research, but the challenge of formulating a program from scratch that I believed would influence astronomy for decades to come was too great to resist,” she said in a NASA interview.
This was a difficult era for women who wanted to advance in scientific research. While Roman said that men generally treated her equally at NASA, she also revealed in one interview that she had to use the prefix “Dr.” with her name because “otherwise, I could not get past the secretaries.”
But she persisted in her vision to establish new ways to probe the secrets of the universe. When she arrived at NASA, astronomers could obtain data from balloons, sounding rockets and airplanes, but they could not measure all the wavelengths of light. Earth’s atmosphere blocks out much of the radiation that comes from the distant universe. What’s more, only a telescope in space has the luxury of perpetual nighttime and doesn’t have to shut down during the day. Roman knew that to see the universe through more powerful, unblinking eyes, NASA would have to send telescopes to space.
Through Roman’s leadership, NASA launched four Orbiting Astronomical Observatories between 1966 and 1972. While only two of the four were successful, they demonstrated the value of space-based astrophysics and represented the precursors to Hubble. She also championed the International Ultraviolet Explorer, which was built in the 1970s as a joint project between NASA, ESA (European Space Agency) and the United Kingdom, as well as the Cosmic Background Explorer, which measured the leftover radiation from the big bang and led to two of its leading scientists receiving the 2006 Nobel Prize in Physics.
Above all, Roman is credited with making the Hubble Space Telescope a reality. In the mid-1960s, she set up a committee of astronomers and engineers to envision a telescope that could accomplish important scientific goals. She convinced NASA and Congress that it was a priority to launch the most powerful space telescope the world had ever seen.
Hubble turned out to be the most scientifically revolutionary space telescope of all time. Ed Weiler, Hubble’s chief scientist until 1998, called Roman “the mother of the Hubble Space Telescope.”
“Nancy Grace Roman was a leader and advocate whose dedication contributed to NASA seriously pursuing the field of astrophysics and taking it to new heights,” said Thomas Zurbuchen, NASA’s associate administrator for science. “Her name deserves a place in the heavens she studied and opened for so many.”
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