The long-awaited detection of gravitational waves has opened up a whole new world of astronomy. One of the key efforts is now to tie signals across multiple domains – for example, a gravitational wave and the associated electromagnetic radiation created by that same event, such as a black hole merger or a gamma-ray burst. We’ll need new equipment to detect such “multimodal” signals, especially electromagnetic ones. One such project is the Black Hole Coded Aperture Telescope (BlackCAT), which will be launched early this year by a team led by researchers at Penn State. 

BlackCAT is designed to replace aging equipment already capturing high energy emissions, such as X-rays, in space. Swift and Fermi, two leading such telescopes, will be at least 10 years over their expected design lifetimes when a series of new gravitational wave detectors come online. Their aging capabilities limit their usefulness in finding the electromagnetic analog of the once-weekly gravitational wave events that those new detectors hope to find.

Enter BlackCAT, a mission concept initially proposed in 2019. It is designed as a 6U Cubesat with one particular detector for “soft” X-ray detection. Soft X-rays are the lower-energy versions of “hard” X-rays typically used in X-ray astronomy. However, they have the added advantage of being easier to detect. They are also easier to isolate to a specific location in the sky, which is essential when mapping a particular EM signal to the source of a gravitational wave event.

To detect those lower-energy X-rays, BlackCAT has two tools in its toolbox—an array of CMOS X-ray cameras and a coded mask imager. The array of cameras, which includes four separate cameras, is called “Speedster-EXD.” It is specifically designed to react quickly to signals but only measures about 2.2 cm2 in size. However, it is still capable of producing a 550×550 pixel image. These cameras have been tested on the ground and have shown sensitivity to the wavelengths of X-rays the mission is designed for.

The coded aperture mask that helps give BlackCAT its name is a tool used to provide a wide field of view for the sensor without needing a focal point – which is hard to design for X-rays that ignore typical focusing devices like lenses and mirrors. Instead, the aperture is a plate designed with a pattern of “open” and “closed” areas that produce shadows on the detector. A computer program can then recreate the original image based on the pattern of shadows that fall across the detector.

This combination of the broad field of view with a highly sensitive X-ray detector seemed right up NASA’s alley, as they funded the project in 2021 to the tune of $5.8M. The detector will interface with an off-the-shelf 6U CubeSat provided by Clyde Space, which includes standardized power, control, and attitude adjustment systems – acting like a platform for the detector. 

PSU’s research team is likely in the final touches of integrating with a launch vehicle, and the plan is to launch BlackCAT early this year. When it gets up there, it can open up a whole new world in X-ray astronomy for a surprisingly low cost. Hopefully, it will show how much can be accomplished by simple, expensive, but very focused CubeSat missions.

Learn More:
Chattopadhyay et al – BlackCAT CubeSat: A Soft X-ray Sky Monitor, Transient Finder, and Burst Detector for High-energy and Multimessenger Astrophysics
Colosimo et al – Current status of the BlackCAT CubeSat
UT – SpIRIT CubeSat Demonstrates a Operational Gamma and X-Ray Detector
UT – A Collection of New Images Reveal X-Rays Across the Universe

Lead Image:
Models of the coded aperture (left) and the BlackCAT Cubesat as a whole (right.
Credit – Colosimo et al.