Artist's impression of a galaxy that is releasing material via two
strong jets (shown in red/orange) as well as via wide-angle outflows
(shown in gray/blue). Both jets and outflows are being driven by the
black hole located at the galaxy's centre.
Black holes, which lurk
unseen at the centres of almost all galaxies, are regarded as one of
the keys to understanding galaxy formation and evolution. Copyright: ESA/AOES Mediala. Hi-Res (JPG)
Stacked telescope mirrors of ESA's current XMM-Newton
Curved mirrors stacked within one of three optical modules of ESA's
XMM-Newton telescope. Each one contains 58 mirrors with a total
telescope optical surface of more than 120 m2 – bigger than a tennis
court. Copyright: ESA
Silicon pore optics mirror stack
A silicon pore optics mirror stack consisting of 35 mirror plates.
The plates are made of silicon wafers. Hundreds of pores allow the
X-rays to propagate through the mirror stack and be reflected on the
coated stripes. Copyright: cosine Research. Hi-Res (JPG)
A silicon pore optics mirror module is mounted in a test adapter for
vibration tests. Acceleration sensors are connected to the module to
measure the vibration levels. Copyright: ESA
A new idea to use super-polished silicon wafers as the heart of a
telescope is set to reveal more of the hot, high-energy Universe,
peering back into its turbulent history.
Invisible X-rays tell us about the very hot matter in the Universe –
black holes, supernovas and superheated gas clouds. Today’s X-ray
observatories, ESA’s XMM-Newton and NASA’s Chandra, were launched in the
last century, and are still delivering world-class science. But they
are starting to age.
To replace them, ESA is planning a much more capable X-ray observatory
for launch in 2028, which would probe 10 to 100 times deeper into the
Universe than the current generation of X-ray telescopes.
“This demands a whole new type of X-ray mirror,” explains Marcos Bavdaz,
leading the technology push for ESA’s future science missions. “To
reach the kind of size needed, this new mission’s mirrors will have to
be 10 times lighter than XMM’s, while delivering even sharper images.”
The problem is that energetic X-rays do not behave like typical light
waves – try to reflect them with a standard mirror and they are absorbed
inside. Instead, X-rays can only be reflected at shallow angles, like
stones skimming along water.
That means multiple mirrors must be stacked together to build a
large-enough telescope. XMM has 174 gold-plated nickel mirrors, nested
inside one another like Russian dolls.
But to reach the performance required for ESA’s next X-ray mission, tens
of thousands of densely packed mirror plates will be needed. How can
this be done?
A new approach is required. ‘Silicon pore optics’, developed by ESA,
draws on high-tech equipment and materials from the semiconductor
industry.
“We make use of industrial silicon wafers, normally used to manufacture
microprocessors,” adds Eric Wille, optical system engineer for the X-ray
optics development.
“We take advantage of their stiffness and super-polished surface,
stacking a few dozen at a time together to form a single ‘mirror
module’.”
Many hundreds of these modules will be fitted together to form the optics of the X-ray mission.
Grooves are cut into the wafers, leaving stiffening ribs and paper-thin
mirrors, which are then covered with reflective metal. For maximum
accuracy, semiconductor manufacturing techniques are applied for the
stacking process.
“Stacking is done by a specially designed robot, aiming for micron-scale
precision,” Eric describes. “We’ve seen big jumps in quality as the
robotics improve.”
“All the stacking takes place in a cleanroom, since tiny dust particles risk large deformations in the mirror stack.
“The semiconductor industry is improving the quality of silicon wafers, which will further improve the mirror quality in future.
Source: ESA
