Optometrist to the stars: MAVIS

A new instrument will give Earthbound astronomers a clear view to rival Hubble

An ambitious collaboration led by Australian, French, and Italian scientists, together with the European Southern Observatory (ESO) located in South America, is aimed at fixing the distortion of images on land-based telescopes caused by the Earth’s atmosphere by designing a giant pair of “glasses” to correct the vision of a Very Large Telescope (VLT) at the ESO.

A new instrument, dubbed “MAVIS” (MCAO Assisted Visible Imager and Spectrograph), will correct for these distortions in real time, delivering crystal clear images and “3D” data portraits of objects millions of light years away.

MAVIS’s images will rival those of the Hubble Space Telescope in detail and clarity, says project scientist Associate Professor Richard McDermid from Sydney’s Macquarie University.

“The telescope that we’re going to put MAVIS on, which has a diameter of eight metres, can collect more light than Hubble, where the main collecting mirror has a diameter of only 2.4 metres,” he says. “The problem is that atmospheric distortions blur the images, meaning we cannot make full use of that larger light collecting ability. That’s where the adaptive optics of MAVIS comes in.”

The team have an ingenious solution to the problem – using lasers and a naturally occurring phenomenon at the edge of Earth’s atmosphere.

“There is a layer of sodium atoms that are deposited by meteors and meteorites in a naturally occurring layer about 90 kilometres up in the atmosphere.

“By hitting these sodium atoms with a laser at exactly the right frequency of light, we can excite them and they glow orange. We use these glowing beacons of light to measure and correct for the Earth’s atmospheric distortions,” says Associate Professor McDermid.

The project was first presented as a concept in 2018 and the design is due for approval this year. MAVIS should be in service by 2027.

“It’s certainly the most complicated instrument that I’ve ever worked on,” says Associate Professor McDermid. “It’s such a delicate operation to work with visible wavelengths of light. Existing adaptive optics systems generally work with infrared light, whose longer wavelengths are less sensitive to optical imperfections. MAVIS works with visible light, like what our eyes see. These wavelengths are much smaller, meaning that MAVIS must be precise on nanometre scales – quite a challenge for an instrument the size of a small truck!”

Scientists get on the same wavelength

What should astronomers look at with the Very Large Telescope?

The new MAVIS instrument can not only take pictures, like a camera, but can also capture 3D information, analysing light waves to build up a “data cube”. Light is broken up into its various colours, which can tell us about the motions and chemical content of gas and stars.

A flagship project will be to investigate intermediate-mass black holes, which we currently know little about.

“Black holes made by individual stars exploding or pairs of stars colliding tend to be in the order of tens of times heavier than the Sun. At the centres of massive galaxies, we see evidence of ‘supermassive’ black holes, which are millions to billions of times heavier than the Sun,” says Associate Professor McDermid.

“But it’s the black holes in between these two ranges that we don’t really know much about, because they’re extremely hard to detect. With MAVIS, we can look deep into the centres of nearby star clusters, where we expect to find these intermediate-mass black holes, if they exist. With the sharp view of MAVIS, we will see the stars moving on the sky over the course of a few years. If they move a lot, they must be orbiting something heavy, and that might indicate the presence of an elusive intermediate-mass black hole.”

This is just one of many exciting areas to explore. “With MAVIS, we will resolve distant galaxies, see the Universe’s first star clusters in formation, detect planetary systems around other stars, and study volcanic eruptions on the satellites of Jupiter” says Associate Professor McDermid. “MAVIS is a tool that will enable a very broad array of science, in the emerging era of high precision astronomy.”