NASA’s Micro-X space telescope is set to launch on August 21 and to operate for just 15 minutes. During its brief time above the atmosphere, it has just one target to study – the supernova remnant Cassiopeia A.
There are two paths to exploring the universe in greater depth than currently possible: build more powerful telescopes or create instruments exquisitely targeted for a single job. One astronomer called the choice the Swiss Army Knife and the scalpel. It’s an exciting feature of our times that plenty of examples of both are under construction.
Few embody the scalpel approach as well as Micro-X, full name high-resolution microcalorimeter X-ray imaging rocket, to be launched from White Sands Missile Range next weekend.
X-Ray astronomy is almost impossible from ground level, even on the tops of high mountains. The atmosphere absorbs too many X-Rays, so the first indication we had of the abundance of X-ray sources was in 1949 after a brief rocket test. Since then, several X-ray telescopes have been placed in orbit to collect data from many sources, but to understand Cassiopeia A, NASA decided to return to the early mode of exploration.
“The supernova remnant is so hot that most of the light it emits is not in the visible range,” said project leader Professor Enectali Figueroa-Feliciano said in a statement. "We have to use X-ray imaging, which isn't possible from Earth.”
Operating a telescope during the brief time it gets above the atmosphere isn’t easy. "Constructing the Micro-X rocket is a challenging endeavor," Figueroa-Feliciano said. "Once it launches, it needs to be a completely hands-off process. It has to turn on, record data, store data and send data back to us autonomously.” Most of the work was done by his students at Northwestern University
Micro-X uses superconducting detectors, which means they have to be kept just a few degrees above absolute zero (-273° C). In the face of the friction generated as it passes through the atmosphere the team placed the telescope in a container of liquid helium.
Although this work will teach the student participants skills, and could also be useful as a prototype, it’s unlikely it would have got funding if the target wasn’t worth investigating, which Cassiopeia A certainly is. It’s a candidate for the youngest supernova remnant in the Milky Way – we’re seeing it as it was less than 400 years after it exploded. In that time it has reached a diameter of about 10 light years, which Figueroa-Feliciano noted means; “The Sun and the 14 closest stars to the Sun would all fit inside.”
At about 11,000 light years away, Cassiopeia A is close for a supernova remnant. Many other remnants lie close to the galactic center, with all the obscuring material that comes with that, but this one is in an outlying spiral, the Perseus Arm.
Already, X-ray satellites and telescopes that operate in other wavelengths have revealed many unexpected aspects of this important site. Just this year we learned one part of the remnant seems to be going backwards, perhaps because part of the shell has run into something substantial.
Cassiopeia A’s an important source of information on which elements get created in supernova explosions, has been replicated in miniature in the lab and was the first supernova remnant whose core was imaged. It might even hold the key to explaining the Fermi Paradox.
This exploded star is even one of those parts of the Milky Way where our electromagnetic observations have been turned into music, so even a brief glimpse using a new instrument could provide compelling data.
1