Jennifer Harbaugh – Imaging X-ray Polarimetry Explorer (IXPE)

Meet IXPE Scientist Abel Lawrence Peirson

Artificial intelligence (AI) has led Abel Lawrence Peirson to all kinds of interesting places. He’s used AI techniques to examine brain activity in flies and other neuroscience applications. With the help of AI, he’s even trained a neural network to create internet memes, displaying phrases on images in a way that looks like a human made them to be funny — at least some of the time.

Now, Peirson, a doctoral student at Stanford University, is using his AI skills to help solve some the universe’s mysteries through NASA’s Imaging X-Ray Polarimetry Explorer (IXPE) mission. It’s a spacecraft that looks at the polarization of X-rays from extreme objects like supernova remnants, neutron stars, and black holes. Polarization describes how the X-ray light is oriented as it travels through space, offering clues to the physics going on in these extreme objects.

To help scientists analyze and interpret IXPE data, Peirson applies a technique called “supervised machine learning.” That means he trains computer models to reconstruct previous events – in this case, the polarization that led to the patterns of X-ray light detection that IXPE sees. It’s kind of like if you see a dented car next to a pole and could reconstruct exactly how fast, and at what angle, the car hit the pole. “We take a really good simulator of the telescope, and then teach the model to reverse” to figure out what kind of polarization leads to IXPE’s detection’s, Peirson explains.

One of the objects he’s interested in is called a “blazar.” A blazar is a special case of an “active galactic nucleus,” composed of a central supermassive black hole that’s actively feeding off material from a surrounding disk, making it appear very bright in the sky. Jets of high-energy particles spew out, and when the jets are oriented towards us, that makes the object a blazar.

A big mystery about these blazars is whether protons, which are some of the subatomic particles that make up the stuff of the world as we know it, contribute significantly to the energy emission from these jets. Protons are examples of “hadrons,” a type of particle that is made of two or more smaller particles called quarks (you may have heard of the Large Hadron Collider, for example). Hadrons may be colliding with particles of light, called photons, and those clashes would produce particles and light in the jets. “So, if we could measure the polarization, this is a really good probe as to whether there are hadronic processes happening,” Peirson said.

Before he got to work on a space mission, Peirson thought that being a professional scientist would mean more doing math and building computer models. While those skills are important, software programming has turned out to be a huge part of his work. “In the end, if you want to be really impactful nowadays, I think that is sort of reality,” he said. “You need to build usable tools or things that people can build on, and that is, like 99% of the time, software.”

One of the biggest challenges of his work is coordinating with a big collaboration. With lots of team members in multiple countries working on IXPE, Peirson quickly realized that science on this mission is not a solitary endeavor. “You’re part of a team and you need to work within the confines of that team,” he said. “Overall, I’m very happy with how it’s turned out.”’

Peirson is multinational — he grew up in London, but his dad is American, and his mom is Spanish. As a child he loved watching Star Trek and reading Isaac Asimov’s novels, both of which sparked his imagination about space and what might be beyond Earth. After earning his undergraduate degree in physics at the University of Oxford, he pursued a Ph.D. at Stanford in Palo Alto, California, where he’s currently finishing up his dissertation.

His advice to future astrophysicists? Learn statistics and programming as soon as you can. “You’re getting data from the sky, in very weird forms that are very unique and difficult to understand, and then trying use models to understand them,” he said. “And that is essentially data science.”

Elizabeth Landau
NASA Headquarters

IXPE Checks Out X-rays from Extreme Objects

NASA’s Imaging X-ray Polarimetry Explorer (IXPE) mission, a joint effort with the Italian Space Agency, has returned data that no other spacecraft has obtained before from a few extreme cosmic objects.

Launched in December 2021, IXPE has detected polarized X-rays from three of its first six targets. Polarized X-rays carry unique details about where the light comes from and what it passes through. By combining these details with measurements of X-rays’ energy and how they change over time, we get a fuller picture of an object and how it works.

Prior to IXPE, the only cosmic object with polarized X-ray measurements was the Crab Nebula, the wreckage of a massive, exploded star whose light swept past Earth nearly 1,000 years ago. In these new observations, IXPE has confirmed the previous Crab Nebula measurements and detected X-ray polarization from a neutron star and a magnetar. A magnetar is a highly magnetic neutron star, a dense object left in the wake of a stellar explosion.

Scientists are now analyzing these preliminary data to better understand what they mean and how they fit in with other observations of these objects.

“Now in its third month of science operations, IXPE is performing as anticipated and is measuring the X-ray polarization of cosmic sources in the high-energy universe,” said Steve O’Dell, IXPE’s project scientist at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “We are excited to see these new results, about a half-century after the pioneering work of IXPE’s principal investigator Martin Weisskopf and look forward to using this new tool to understand better the workings of neutron stars, black holes, and more.”

Weisskopf was part of a team from Columbia University that first detected polarized X-rays from the Crab Nebula in 1971 using a sounding rocket experiment. About five years later, in 1976 and 1977, the Columbia team used NASA’s eighth Orbiting Solar Observatory (OSO-8) to confirm that X-rays from the Crab Nebula are polarized by a degree of almost 20 percent. IXPE measures the polarization of X-rays with higher precision, but its preliminary results agree with observations from OSO-8 and more recent measurements taken by a small satellite called PolarLight.

Composite image of the Crab Nebula with X-rays from NASA’s Chandra X-ray Observatory (blue and white), optical light from NASA’s Hubble Space Telescope (purple), and infrared light from NASA’s Spitzer Space Telescope (pink).
Credits: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech

Another object IXPE has looked at recently is the magnetar 4U 0142+61 in the constellation Cassiopeia. The third object that IXPE detected polarized X-rays is the binary accreting neutron star system Hercules X-1, which consists of a low-mass star and a neutron star that is pulling material off it.

The other targets for IXPE’s first science observations were the supernova remnant Cassiopeia A and the active galaxy Centaurus A, as well as the Sagittarius A Complex at the center of the Milky Way, a region that includes the black hole Sagittarius A*. Preliminary analyses have not detected X-ray polarization from these objects so far, but more detailed analyses are underway.

IXPE’s first datasets are now publicly available through NASA’s High Energy Astrophysics Science Archive Research Center, managed by the agency’s Goddard Space Flight Center in Greenbelt, Maryland.

IXPE Unfolds its Origami Boom for Science

NASA’s newest X-ray observatory – the Imaging X-ray Polarimetry Explorer, or IXPE – extended its boom successfully Dec. 15, giving IXPE the ability to see high-energy X-rays. The mission, which launched on Dec. 9, is one step closer to studying some of the most energetic and mysterious places in the universe in a new way.

A gif of IXPE deploying in space before starting its science operations to study the cosmos.

The IXPE observatory features three identical telescopes, each with a mirror assembly and a polarization-sensitive detector. To focus X-rays, IXPE’s mirrors need to be about 13 feet (4 meters) away from the detectors. That’s too large to fit inside some rocket fairings. So IXPE’s boom had to fold up, like origami, into a 12-inch (0.3-meter) cannister and stretch out again in orbit.

“For those of us in the space game, moving parts are always frightening,” said Martin Weisskopf, IXPE’s principal investigator at NASA’s Marshall Space Flight Center. “Right now, I’m smiling from ear to ear.”

With the boom now deployed, mission specialists are ready to focus on commissioning the telescopes, preparing them for the spacecraft’s first science.