Astronomy has a blind spot in the area of far-infrared radiation compared to
most other wavelengths. A far-infrared space telescope can only utilize its
full sensitivity with an actively cooled mirror at temperatures below 4
Kelvin (-269 ℃). Such a telescope doesn't exist yet, which is why there has
been little worldwide investment in the development of corresponding
detectors.
In 2004, SRON decided to break this cycle and invest in the development of
Kinetic Inductance Detectors (KIDs). Now, researchers from SRON and TU Delft
have achieved the highest possible sensitivity, comparable to feeling the
warmth of a candle on the moon from Earth. Their study appears in Astronomy
& Astrophysics on September 6th.
In recent years we have been spoiled with the most beautiful pictures from
telescopes working with X-rays, infrared, radio and visible light. To name a
few: the image of the black hole in M87, the Hubble Extreme Deep Field or
the baby picture of a planetary system. But in one wavelength area,
astronomy is relatively blind: the far-infrared, especially at wavelengths
between 300 μm and 10 μm.
The Earth's atmosphere blocks most of this radiation for ground-based
telescopes, while space telescopes often have a temperature such that they
blind their detectors with the far-infrared radiation they emit themselves.
With so much noise, there is little incentive to commit large sums of money
to the development of more sensitive far-infrared detectors. And with a lack
of sensitive detectors, governments won't allocate funds to super-cooled
noiseless telescopes.
Breakthrough
At the start of this century, SRON decided to break the pattern and invest
in the development of Kinetic Inductance Detectors (KIDs). That decision is
now bearing fruit. Together with the TU Delft, SRON researchers have almost
perfected the technology by making it sensitive enough to see the permanent
background radiation of the universe.
"An even higher sensitivity would have no use," says Jochem Baselmans
(SRON/TU Delft). "Because you will always be limited by the noise of the
universe's background radiation. So our technology provides telescopes
builders such as NASA and ESA with far-infrared detectors as sensitive as
possible. We already see two proposals submitted to NASA for a super-cooled
telescope. Those are much more expensive than relatively warm telescopes,
but our KIDs make it worth it."
Terahertz gap
KIDs help astronomy to close the terahertz gap, named after the frequency of
far-infrared light. Astronomers are now missing out on light produced by
stars in the far-away, young universe, leaving a gap in our knowledge of
stellar evolution. Moreover, the terahertz gap is a unique opportunity for
adventurous astronomers to dive into the unknown.
"You don't know what you don't know. The Hubble Deep Field was created by
pointing the Hubble telescope at a pitch-black piece of the sky with
seemingly nothing in it. Afterwards, thousands of galaxies emerged, from an
area smaller than one percent of the full moon," says Baselmans.
The sensitivity that the researchers achieved with their KIDs can be best
described by a hypothetical candle on the moon. Imagine standing on Earth—or
floating just above the atmosphere—and holding up your hand to feel the
candle's warmth. Seems like a futile exercise? Not for a KID. It is even ten
times more sensitive than that. With an integration time of a second, a KID
can detect as little as 3*10-20 watts.
Reference:
J.J.A. Baselmans et al, Ultra-sensitive Super-THz Microwave Kinetic
Inductance Detectors for future space telescopes, Astronomy &
Astrophysics (2022).
arxiv.org/abs/2207.08647
Tags:
Space & Astrophysics