100K-pixel X-ray imager will unravel invisible universe

NASA, MIT, and NSIT's new microcalorimeter has an energy resolution two orders of magnitude greater than that of an X-ray CCD camera.
Chris Young
The prototype 100,000-pixel magnetic calorimeter array.
The prototype 100,000-pixel magnetic calorimeter array.


Over the last five years, a NASA team has collaborated with scientists from MIT and the National Institute of Standards and Technology (NSIT) to develop an ambitious new X-ray camera with unprecedented imaging and spectroscopic capabilities.

Their work constitutes a technological advancement for a new type of X-ray microcalorimeter called a magnetic microcalorimeter, a blog post from NASA reveals. These operate at very low temperatures — as low as only a few tens of milli-Kelvin above absolute zero.

The new advancement could dramatically improve the global astronomical community's capacity for analyzing X-ray light that would otherwise be invisible to the naked eye. This, in turn, will allow them to peer into galaxy cores and uncover the mysteries of cosmic evolution.

A groundbreaking 100,000-pixel X-ray camera

The NASA, MIT, and NSIT collaboration has developed X-ray arrays of 100,000 pixels or more. Each pixel in the arrays is designed to have an energy resolution roughly two orders of magnitude greater than that of an X-ray CCD camera.

As a point of reference, NASA and JAXA have collaborated on an X-ray imaging and spectroscopy mission called XRISM, which was recently delayed but is due to launch in the coming weeks. That mission's spacecraft features a microcalorimeter array with 36 pixels.

Another mission, the European Space Agency's (ESA) ATHENA, will have a microcalorimeter array of approximately two thousand pixels.

By comparison, the new NASA arrays reach "angular scales and array sizes normally only associated with charged-coupled device (CCD) cameras," the US space agency explains in its post.

"This exquisite high-energy resolution is critical to measure the abundances, temperatures, densities, and velocities of astrophysical plasmas," the post continues. "Such measurements will expose the essential drivers of galaxy evolution that are hidden in the plasmas of the universe."

How does NASA's new microcalorimeter work?

The microcalorimeters use an absorber to detect incoming X-rays. When an X-ray hits this absorber, it is converted into heat, which is then measured using a thermometer in the instrument. The rise in temperature is directly proportional to the X-ray's energy.

Magnetic microcalorimeters use thermometers with paramagnetism to allow for highly accurate temperature readings, allowing them to provide high-precision X-ray readings.

To date, the biggest hurdle for microcalorimeter innovation has been the challenge of fabricating the high-density, high-yield superconducting wiring required to connect all the pixels in an array.

The NASA, MIT, and NSIT team claim to have overcome this obstacle by incorporating many layers of buried wiring underneath the top surface of detector chips over which the arrays are then fabricated. MIT was responsible for developing a process that allows over eight layers of superconducting wiring with high yield.

NSIT, meanwhile, is developing a microwave-multiplexer superconducting quantum interference device (μ-MUX SQUID) read-out, which will allow measurements for such large arrays of pixels.

According to the NASA post, "to truly understand how galaxies form, X-ray observations from high-energy resolution imaging spectrometers are needed to see the cores of the galaxies themselves."

"New large-area, high-angular-resolution, imaging X-ray spectrometers will expose the essential drivers of galaxy evolution, which leave imprints in the warm-to-hot plasma that cosmologists believe exists in the spaces between galaxies. These intergalactic spaces contain 40%–50% of the "normal matter" in the universe and extend well beyond the currently visible size of galaxies."

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