NASA's latest triumph, the Nancy Grace Roman Space Telescope, will be unique in dumping 1.4 terabytes of data onto the internet every day with a clear message to astronomers and citizen scientists alike: Have at it!
That's where UC Berkeley's Jessica Lu comes in. She and David Weinberg of Ohio State University have created a collaboration of scientists - nearly a thousand and growing - that has been meeting regularly for the past 18 months to determine the most efficient way to digest this daily deluge and mine it for new science.
"Roman is very different from all of our previous space telescopes," said Lu, a Berkeley associate professor of astronomy. "The telescope takes the data, and within 48 hours it's available to the entire world. As a result, we're planning to do science differently as well. The Roman Science Collaboration is a group of 900 astronomers that are interested in working together collectively to get out the highest-impact discoveries from the survey data."
Roman, named for NASA's first chief astronomer, is designed to survey the sky regularly in search of subtle and not-so-subtle changes: a supernova explosion, the weird dance of a star when it passes behind a massive object like a black hole, or a brief flash of light that quickly fades away. "Things that go bump in the night," Lu said.
Courtesy of Jessica Lu
Though the telescope has a long-term plan for different types of surveys - to map galaxies, explore the mystery of dark energy, image dim planets around stars - everyone ultimately gets the same firehose of data.
"Every time Roman is looking at something, it is looking at a thousand somethings or a hundred thousand somethings," Lu said. "So you need a large community of astronomers to come together to figure out how to make the most of all of that data and all of the objects in just one pointing of Roman."
Launched Aug. 30, Roman has a history entwined with Berkeley. Back in 1999, Berkeley physicist Saul Perlmutter and colleagues at Lawrence Berkeley National Laboratory proposed a space telescope dedicated to studying the enigmatic dark energy that permeates space and is accelerating its expansion. He contributed to the planning of several iterations of the telescope to make sure it had the right cameras and spectrographs to go beyond ground-based studies of the expanding universe by peering farther into the cosmos.
"In 1999 we were trying to make the case that, with a wide field imager and some spectroscopy, we could actually make a big difference in understanding what the dark energy story was," said Perlmutter, the Franklin W. and Karen Weber Dabby Professor in the Department of Physics. "That's basically what we ended up with now, with the Roman, in terms of near-infrared."
Free-floating black holes and other oddities
The space telescope, with its 2.4-meter mirror, is now on its way to a spot nearly a million miles from home where it will forever loiter as it accompanies Earth around the sun. It could begin its three major surveys as early as December. One of these focuses on the area around the center of our Milky Way Galaxy - the so-called galactic bulge - and involves taking snapshots of six separate regions of the sky every 12 minutes with its 288-megapixel near-infrared camera, the Wide Field Instrument. The goal is to detect the bending of light caused by dark objects: exoplanets, solitary or binary black holes or neutron stars, failed stars called brown dwarfs, free-floating planets or any other dim object. The subtle shift, called microlensing, is caused by the warping of spacetime by gravity.
"There are over 200 planets that have been found with microlensing so far, but mostly they're more massive planets. Neptunes and Jupiters, not many Earths," Lu said. "Roman should be able to find several thousand planets with the gravitational lensing technique and over 100 Earth-mass planets in Earth-like orbits. And that is not something we've ever been able to do before."
Lu is particularly interested in more massive microlensing objects - black holes. Her team was one of the first to find a free-floating black hole in the Milky Way Galaxy, in 2022, but Roman should find many more. Over the past decade, she actively lobbied NASA's Roman team to slightly modify its exoplanet survey to improve chances of detecting dark black holes.
"We tried to persuade them that Roman could be a black hole-finding machine, not just an exoplanet and cosmology machine," she said. Over the course of the five-year survey, the telescope is expected to find 30,000 microlensing events - many of them exoplanets. But Lu expects to uncover a few hundred dark black holes as well.
The telescope will also make infrared measurements and record spectra that can be used for a wide variety of other studies. The goal of the consortium is to parcel out the relevant data to groups of scientists with similar interests and encourage collaborations that maximize the chances of discovering something new from the observations.
"We're bringing scientists together into one place, with all of their varied expertise, to try and make the most of the Roman data," she said.
From SNAP to WFIRST to Roman
For Perlmutter, the telescope is the culmination of a 27-year dream to have a space instrument capable of charting the history of cosmic expansion. A member of the Roman collaboration, he has participated in many of the formulation teams for Roman and even led one of them.
Christopher Michel
Not long after he and his team discovered that the expansion of the universe is accelerating - an effect attributed to dark energy - he, Michael Levi and colleagues at Berkeley Lab developed a concept for a space telescope dedicated to discovering the cause of the acceleration. They garnered the full financial support of the U.S. Department of Energy, pulled together a collaboration of 140 scientists at some 15 international institutions, built a mock-up of the spacecraft - which they dubbed SNAP, for Supernova Acceleration Probe - prototyped and tested detectors and a spectrograph, and purchased the glass blank for a 2.4-meter mirror. They even set a launch date: 2008.
But the powers that be decided that the DOE project should become a joint DOE/NASA project and acquire a new name: the Joint Dark Energy Mission (JDEM). Eventually DOE dropped out, and the mission's scope expanded to include an exoplanet search - both dark energy and exoplanets are top U.S. science priorities. Then, in 2010, the project got a new name: the Wide Field Infrared Survey Telescope, or WFIRST. When the U.S. Department of Defense offered to give NASA an unused high-resolution mirror originally built for a spy satellite, that freebie became the centerpiece of the Roman telescope.
The technique that Perlmutter and his team use to measure the expansion of the universe - also employed by a rival team that found an accelerating expansion at the same time and shared with Perlmutter the 2011 Nobel Prize in Physics - is to search space for Type Ia supernovae. Because they explode with a known brightness, they can serve as standard candles; it's straightforward to calculate how far away they are (and hence how far back in time we are seeing them) based on how bright they appear from Earth. And the stretching of the light's wavelength, or its redshift, is exactly a measure of how much the universe has expanded since the supernova explosion, since light stretches with the expansion. Both teams found that the expansion rate is higher for more recent supernovae. In other words, the expansion of the universe is accelerating.
Roman will look for more Type Ia supernovae, at greater distances, to see how this acceleration has changed over the course of cosmic history. In the sweet spot for the telescope, Perlmutter said, are supernovae between about redshift 0.7 and 1.5, spanning a range from about 6 billion to 10 billion years into the past. Though Roman can see extremely bright supernovae beyond that distance, without the ability to detect a wide range of brightnesses, calibrating Type Ias as standard candles becomes harder.
Roy Kaltschmidt photo courtesy of Lawrence Berkeley National Laboratory
Roman will be crucial to resolving the current ambiguity surrounding dark energy. Ground-based supernova measurements by Berkeley Lab's DESI collaboration - the Dark Energy Spectroscopic Instrument - and a variety of other observations show hints that the accelerating power of dark energy has been changing over time. Perlmutter suspected decades ago that this might be the case, but the uncertainties in mapping supernovae were large enough to obscure the trend. No longer.
"Within the last couple years, the combination of supernova measurements and a new technique of baryon acoustic oscillation measurements combined with good measurements of the cosmic microwave background are showing hints that dark energy is varying in time in a way that is somewhat surprising," he said. Baryon acoustic oscillations are large-scale fluctuations in the density of protons and neutrons, which can also be used as a measure of cosmic distance.
One theory is that a "phantom energy" accelerated the expansion and increased dark energy density until around 5 billion years ago, when it began to decay away.
Roman will look back to that distant time, which was also an era when dark matter dominated over dark energy and normal matter. Today, the reverse is true: dark energy makes up 68% of the universe's matter and energy, compared with 27% for dark matter and 5% for the normal matter we see, such as stars and gas.
A private space telescope: Lazuli
One key aspect of SNAP that was left out of Roman was a high-resolution spectrograph that would help in establishing the intrinsic brightness of any Type Ia supernova detected. While Roman has a spectrograph, it's not good enough to discriminate among subtle subtypes of Type Ias at higher redshifts. Several years ago, Perlmutter asked Eric Schmidt, a Berkeley alum and former Google CEO, to fund a private telescope dedicated, in part, to spectroscopy sensitive and accurate enough to achieve this goal for the entire redshift range. Schmidt got excited about the project, Perlmutter said, and eventually committed to building the 3-meter Lazuli Space Observatory in addition to three ground-based observatories. All could be up and running by late 2028 or 2029, with the possibility that Lazuli could be launched aboard a new rocket built by Relativity Space, a space-launch company that Schmidt purchased in 2025.
Schmidt Sciences
Lazuli, designed for precise observations across visible and near-infrared wavelengths, will complement Roman by providing high-quality spectroscopy for many thousands of supernovae at redshifts spanning the whole range - up to 1.5. The aim is not only to check the current indications of time-varying dark energy, Perlmutter said, "but to provide a next-generation history of dark energy's properties that will help uncover its identity."
"We're living in a really exciting period of dark energy studies," he said. "In the end, if the Roman supernova survey works and the spectrograph on Lazuli works, we finally should be able to make the measurements that we had intended to make back in 2008, but we'll be making them in 2028. They will still be extremely welcome - we still want to understand what most of the universe is made of."
Roman will also map galaxies to reconstruct the 3D structure of the universe, shedding light on both dark energy and dark matter.
Altogether, some 20 scientists across the Berkeley campus and Berkeley Lab, representing an array of astronomical interests, are part of the Roman Science Collaboration, which is now working on the best pipeline to get Roman data analyzed quickly to maximize its impact on our understanding of the universe.
In her own lab, Lu said, postdoctoral students, graduate students and "an army of undergraduates are all trying to figure out how to improve the computational efficiency of our codes, because when we move from analyzing one target at a time to analyzing hundreds of targets, your code better run a lot faster."
Perlmutter emphasized Berkeley's leadership role this century in astrophysics and cosmology, having instigated two major telescopes in space, Roman and Lazuli, and a major successful Berkeley/Berkeley Lab-led ground-based project, DESI - which grew out of SNAP; and having tackled dark energy with the baryon acoustic oscillations technique.
"Together with our leadership in cosmic microwave background measurements, Berkeley continues to play an unusual formative role in the major cosmology measurement approaches," he said. "It's a great place to be if you want to learn about the universe!"
