On Thursday, December 9, the agency will launch the Imaging X-ray Polarimetry Explorer, known as IXPE, on a Falcon 9 rocket from NASA’s Kennedy Space Center in Florida. It will be the first x-ray telescope capable of measuring polarization, a property of light that describes the orientation of its electrical and magnetic energy.
X-rays are high-energy light waves made up of electromagnetic radiation, and they’re especially abundant in space. Much of the light we see in the world is unpolarized, which means it’s made up of electric and magnetic energy with no specific direction. Polarized light, whose electric and magnetic energy points in a single direction, is useful because it can carry information about the magnetic fields and chemical composition of matter with which it interacts.
IXPE has three telescopes, each equipped with a set of mirrors and a detector that’s able to track and measure four properties of light: its direction, arrival time, energy, and polarization. Data about the incoming x-rays from all those detectors is combined to create an image. Scientists hope to use IXPE’s images to refine their theories about different celestial environments and the objects inside them.
For example, the explorer could provide new clues about why black holes spin and reveal more about the unique structure and behavior of astronomical objects like the famous Crab Nebula, a rapidly spinning neutron star.
IXPE is set to observe more than 50 of the most energetic known objects in the universe in the next two years, including the supermassive black hole nestled in the middle of the Milky Way. All these objects emit x-rays, and measuring polarization will allow IXPE to make detailed observations of them.
“[IXPE] is going to look at the really wonderful zoo of neutron stars and black hole systems, [in] and out of the galaxies,” says Martin Weisskopf, chief scientist for x-ray astronomy at NASA’s Marshall Space Flight Center and principal investigator for IXPE.
Weisskopf is especially interested in determining whether these objects have strong magnetic fields—a task that can be done with other instruments but will be made easier with IXPE. But Gregory Sivakoff, an associate professor at the University of Alberta, says IXPE’s discoveries could have broader implications, particularly in advancing our understanding of black holes.
“It turns out that there are only really three things that you can measure about the properties of a black hole: its mass, its spin, and its charge,” says Sivakoff. “I’m really interested about the ability for IXPE to give us a new way of measuring the spin, and possibly even checking to see if there are any changes to that spin over a long enough time.”
Black holes make up about 40% of the dark matter in the universe, but only recently were astronomers able to photograph one. The data IXPE will bring back will help determine whether black holes once actively fed on their neighbors and make it easier for scientists to study the particles that exist around these powerful objects. With x-ray polarization, it’s also possible to map the inner edge of a black hole by measuring its angular momentum, or spin.
Since supermassive black holes and neutron stars are the remnants of massive stars that lived fast and died young, IXPE’s mission could also give us a glimpse of how galaxies evolve, Sivakoff adds.
Herman Marshall, a research scientist at the MIT Kavli Institute for Astrophysics and Space Research and a co-investigator for IXPE, says measuring polarization “is like putting up a mirror, you might say, to the unseen part of the galaxy.” Here’s hoping that once IXPE turns its eyes toward the stars, the galaxy won’t mind parting with a few more of its secrets.
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