Researchers present a super-fast camera for exoplanets

In the years since astronomers discovered the first exoplanet, a planet that orbits a star outside the solar system, more than 4,000 have been observed. Usually, their presence is revealed by the slight effects they have on their parent stars, which cloud them enormously. For a decade and a half, scientists have been trying to visualize exoplanets directly, but Earth’s atmosphere is a major obstacle when attempting to exploit Earth’s large telescopes.

Now, a team of US and Japanese scientists and engineers including UC Santa Barbara researchers has developed a new camera for hunting exoplanets. Deployed at the Subaru Telescope on Maunakea, Hawai’I, the device is the world’s largest superconducting camera by number of pixels and will pave the way for direct imaging of extra-solar planets in the near future. An instrumental document that appeared in the publications of the Astronomy Society of the Pacific announced the new device to the astronomical community.

Built by researchers in Professor Ben Mazin’s laboratory, the MKID Exoplanet Camera (MEC) uses Microwave Kinetic Inductance Detectors (MKID) to allow scientists to directly visualize exoplanets and disks around bright stars. The detector operates at a brisk 90 millikelvin speed – just a touch above absolute zero – and is the first permanently deployable superconducting camera operating in the optical spectrum and near infrared.

“In direct imaging of exoplanets, you are trying to imagine planets that are millions of times fainter than their parent stars,” said Sarah Steiger, a doctoral student in the Mazin lab who worked on the MKID pipeline. “It’s the equivalent of trying to see a firefly next to a football stadium that is fully lit by an airplane.

“Also, if you do it from the ground, you have to look through the turbulent atmosphere of the Earth,” he continued. This turbulence is what makes stars shine in the night sky and is a perennial headache for astronomers, distorting images and projecting starlight onto faint exoplanets.

“It’s a constant battle to prevent the star’s scattered light from completely engulfing the planet,” said PhD student Neelay Fruitwala.

Modern observers use adaptive optics to correct these distortions. The systems rely on rapid feedback loops and complex algorithms to bend a telescope’s mirror thousands of times per second in ways that counteract the effects of the atmosphere, allowing scientists to retrieve an image as if the telescope were in space.

“These very complicated adaptive optical systems allow us to discover planets like the ones in HR 8799, which is a system with four planets all above the mass of Jupiter orbiting within it,” Mazin said. But they can also scatter light, which obscures faint exoplanets. “We found that just using adaptive optics alone would have found us only a handful of planets, namely those that still glow with the warmth of their formation, which are not that common in our stellar neighborhood.”

Another advantage of MKIDs lies in their ability to determine the energy of each photon hitting the detector. “This allows us not only to determine the brightness of a planet,” said Steiger, “but also to obtain a spectrum (brightness as a function of energy), which can reveal further information about the properties of an exoplanet, such as its age, mass and potentially atmospheric composition. “

More advanced detectors use a coronograph, which blocks some of the light from the host star so that scientists can better discern light reflecting on the planet itself. This is important for imaging neighboring systems, most of which are not particularly young. However, getting the best performance from such a setup requires extremely good adaptive optics.

“These tools are hitting a wall right now,” Mazin said. “They can block the light from the star by about a factor of a million, but the problem is that most planets are more like a billion times fainter than their parent star.”

An advantage of MKIDs over traditional cameras is that they are very fast. These detectors can read data thousands of times per second, which are the speeds required to keep up with an adaptive optics system, Steiger explained. This allows a MKID to further clean up an image by communicating with the observatory’s adaptive optics system to remove some of the scattered and diffracted starlight. This pushes the limits of what a faint exoplanet can be visualized.

The MKID Exoplanet Camera is expected to expand the range of exoplanets that astronomers can photograph directly to those close to Earth. These are the most important because we can characterize them in greater detail, said co-author Olivier Guyon, the project scientist responsible for the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument.

The ultimate goal is to seek evidence of life and the MEC is an important step on this journey. “We won’t be able to do this with Subaru, or any of the current telescopes, because they’re just a little too small,” Guyon said. “But we are preparing for the next big step, which is to install exoplanet imaging cameras on larger telescopes like the Thirty Meter Telescope. When those telescopes go online, the same technologies, the same camera, the same tricks will allow us. to do so. really look for life “.

That said, there is still a lot of work to be done, mainly on the software and algorithms of the MEC. The team received a large grant from the Heising-Simons Foundation to address this problem and further develop rapid optical correction in the coming years. “We are throwing every trick in the book at this one,” Mazin said, “and we are also developing new tricks.”

The authors recognize the significant cultural role and reverence that the peak of Maunakea holds within the Hawaiian community and said they feel fortunate to have the opportunity to conduct observations from this mountain.