Astronomers are pulling out all the stops: A telescope tethered to a football-stadium-sized balloon, a camera the size of an SUV and twice as heavy nestled in the Chilean mountains, a tiny blue cube filled with chilled liquid argon sitting in a Northeastern lab destined for balloon flights. And, of course, the James Webb Space Telescope.
These collaborative, international experiments sit at the forefront of astrophysics and cosmology research. Northeastern’s newest physics professors and their students are working on all of them. The collaborations are aimed at solving cosmology’s biggest open problem: We can’t see 95 percent of the “stuff” in the Universe. So, what the heck is it?
“It’s kind of scary that we don’t really know what most of [our Universe] is made of,” says Arathi Suraj, a Ph.D. student working in one of the new Northeastern labs. “So this is our way of trying to find out what’s going on.”
The search for this missing stuff that scientists call dark energy and dark matter is gaining momentum. Telescope technology has advanced rapidly, the public is fascinated, and the funding for research is flowing. Northeastern’s new astrophysics labs — with its three recent hires and their handful of postdocs, Ph.D. students and undergraduate researchers — are trailblazers.
The “dark” side of the Universe
Dark energy and dark matter are enigmas that control how the Universe will evolve and how the regular matter that we can see — from planets to stars to intergalactic space dust — moves, clumps and expands.
Dark matter was discovered from the gravitational force it exerts. Ever since Newton, scientists have carefully measured gravity to understand the relationship between the mass of an object and the strength of the object’s gravitational force. But in the 1930s, astronomers observed a galaxy cluster that behaved as though it were more massive than their math predicted. They then made a bewildering discovery: Whatever was creating this extra gravitational attraction wasn’t a fluke in one galaxy cluster; the stuff was everywhere. Astrophysicists named the mysterious source of this extra gravity dark matter.
Dark matter doesn’t emit, block or reflect light, so it is extremely difficult to study. But astronomers have been mapping it by looking at the way its gravity bends the light from the galaxies behind it — similar to a magnifying glass distorting light — in an effect called gravitational lensing.
The method is popular for a reason: “The thing I like about gravitational lensing is that it is agnostic to what the dark matter is made of,” says Jacqueline McCleary, the most recent of the new astrophysics hires. As far as the force of gravity is concerned, “dark matter could be anything … It doesn’t matter” what creates it.
In the 1990s, astronomers were bewildered again. They observed that the Universe, which they assumed was stationary and stable, was expanding and doing so at an ever-accelerating rate. The expansion was caused by massive amounts of energy apparently hiding throughout the Universe. Astronomers called it dark energy.
Based on current dark energy theories, the galaxies in the Universe will stretch so far apart that in 100 billion years, the number of galaxies we could see in the night sky will have diminished from hundreds of billions to a measly two, along with a couple dozen smaller dwarf galaxies.
Ironically, one popular method to measure the amount of dark energy in the Universe is using the maps of dark matter. Astrophysicists can determine precisely how much the Universe has expanded at each point in its history by looking at how the structure of the dark matter web, mapped by gravitational lensing, has grown in size over the eons.
“They call it the Cosmic Web,” says Jonathan Blazek, the first of the new hires. “And as you change the theory of dark energy or the theory of dark matter … you get different looking webs.”
After decades of measuring the amount of dark matter and dark energy in the Universe, the conclusion is: only a measly five percent of the Universe is made of regular matter that we can see and interact with. The rest is a mystery, and to make detailed observations of it, we need resources and advanced technology.
“We’re in a field where you just can’t do this in a lab anymore,” says Blazek. “You need the resources of multiple countries and hundreds — if not thousands — of people.”
Astrophysics and cosmology collaborations thus far, including Hubble, have produced a plethora of discoveries in dark matter and dark energy. In fact, the discovery of dark energy itself came from Hubble observations. Now, the community leans in on the handful of flagship observation projects capable of peering past the frontier of our knowledge.
This shift has meant that most observational space science is now coordinated by governments and international organizations. Nine Hubble-sized missions for space telescopes and ground observatories are currently under development. NASA, the primary funder of astrophysics research in the U.S., has almost tripled its investment over the past decade.
“We have some of the greatest scientific tools in human history. And we are well-poised to … tackle these mysteries in the Universe,” says McCleary.
The professors studying cosmology’s biggest questions
Jonathan Blazek and models of dark energy
Blazek, who joined Northeastern in 2020, heads the modeling and analysis team at the Dark Energy Survey collaboration, where he helps model the evolution of the early Universe into the modern Universe. The team compares these simulation results to experimental observations from a house-sized telescope at the Cerro Tololo Inter-American Observatory in the Chilean mountains. They’ve found that the most well-supported theory of cosmology, which accounts for dark matter and dark energy, has two parameters that just aren’t evolving correctly.
First, the clumpiness of dark matter — how much it tends to concentrate in certain areas as opposed to lying evenly over all space — isn’t evolving as expected in the models. The dark matter in the Universe seems either too evenly spread in the modern Universe or too clumpy in the early Universe, depending on who you ask. Additionally, the Universe is expanding much faster than expected.
These discrepancies are strong indications that new physics explanations of dark matter and energy are just beyond our reach. But the dark matter map “gives you these sort of lamp posts that you can look under for promising theories,” says Blazek.
Now, Blazek and many of his colleagues are starting work on the next even bigger dark energy collaboration: the Legacy Survey of Space and Time. They’re using a bigger camera — weighing over 6,000 pounds — and a telescope over twice as large and only a 30 minute drive south, at the Vera C. Rubin Observatory. The collaboration aims to collect 500 times more data than the Dark Energy Survey, providing an even bigger lamp post to test theories under.
Jacqueline McCleary and maps of dark matter
McCleary works on data analysis and processing for ground, sky and space observation collaborations that map dark matter webs. She joined the collaborations as they were getting off the ground during her postdoc at NASA’s Jet Propulsion Laboratory in California and brought them to Northeastern as a faculty member in 2022.
“It turns out that my skill set is one of software development, image analysis [and] bias quantification — all of this really detailed, annoying work that needs to get done to make these gravitational lensing measurements,” says McCleary.
One of McCleary’s collaborations, SuperBIT, started as a bold and unconventional proposal: suspend a telescope from a giant balloon — the size of a football stadium — and let it float 20 miles up, above 98 percent of Earth’s atmosphere. Here, it’s unobstructed by the atmosphere, with a view similar to space-based telescopes at only a fraction of a percent of the cost. The telescope succeeded in its first 40-day science mission in late spring, providing a stunning view of the Tarantula Nebula with bright red, purple, and pink gas filaments weaving and twisting around speckled clusters of stars.
McCleary is also a member of a collaboration working with NASA’s flagship James Webb Space Telescope (JWST). She simulated what distant galaxies might look like to JWST, which helped the collaboration to win 255 hours of intensely sought-after observation time on the premiere space telescope in the world. Now, her team is helping translate JWST’s observations of galaxies, distorted through gravitational lensing, into dark matter maps.
Tsuguo Aramaki and dark matter particles
Tsuguo Aramaki searches for dark matter particles that interact almost exclusively with gravity. These theoretical particles include WIMPs, weakly interacting massive particles.
Aramaki is working on a new advanced project, called the Gamma-Ray and AntiMatter Survey (GRAMS), which will float up in a weather balloon and search for particles from space that result from the decays and interactions of dark matter particles. It’s an evolution of the detector he’s been working on since his grad school days. By updating conventional detection methods and searching for particles at unexplored energy levels, GRAMS is more sensitive to potential WIMP signals than its predecessor.
Collaborators in Japan just completed the program’s first successful engineering test flight with a small-scale detector. Now, the U.S. team, including Northeastern, Columbia, NASA and other institutions, are readying a new iteration of the detector for an engineering test flight in an Arizonan desert before it begins scientific flights.
Aramaki’s lab is located in the same hallway as Blazek and McCleary’s joint lab space. The researchers in the professors’ labs frequently ping each other for input when stuck on a problem. All are intensely interested in the work, and many chose physics research because of the awe behind these weird, cosmic mysteries.
“We need a young generation. We are doing something new — we need to do something new. So, we need new brains,” says Aramaki.
Story from the Science Media Lab.
Last Updated on August 24, 2023