Three Hawai‘i telescopes add color to new space mission aimed at mapping the universe in 3-D

What is the universe made of? What is the mysterious dark matter? How has the structure of the universe evolved throughout billions of years?

After twelve years of planning, the European Space Agency on July 1 launched its Euclid satellite from Cape Canaveral, Fla., with the goal of answering those and many other questions, and it will get a big — and colorful — helping hand from three observatories in Hawai‘i.

Prior to Euclid’s launch, the work of creating a three-dimensional map of the universe began through the UNIONS project, an ambitious imaging survey of the northern sky in the optical and near-infrared conducted since 2017 by the Canada-France-Hawaiʻi Telescope and Subaru Telescope atop Maunakea on the Big Island and the University of Hawaiʻi Institute for Astronomy Pan-STARRS telescope on Haleakalā on Maui. The Euclid mission will continue that work from space.

“The superb observing conditions in Hawaiʻi led to the unprecedented collection of galaxies over a very large area of the sky, with each telescope playing a critical role by adding different filters or colors to the Euclid data” said Jean-Charles Cuillandre with CEA Saclay at the Université Paris-Saclay, who is also a former staff astronomer at Canada-France-Hawaiʻi Telescope. “While a critical part of the original motivation to obtain the UNIONS data was the Euclid mission, the data will have an impact extending far beyond the space mission.”

But Euclid has only four filters — one that spans most of what can be seen as visible light and three that cover infrared wavelengths. The Hawaiʻi telescopes will add observations in five visible-light filters, spanning the rainbow from the violet to far-red. In other words, the telescopes turn the black-and-white 2-D images from Euclid into a full color, 3-D map of the universe. The Canadian Astronomy Data Centre will also provide color information based on observations from the Hawaiʻi-based observatories.

UNIONS is co-led by Cuillandre, Ken Chambers at the Institute for Astronomy, Alan McConnachie at Dominion Astrophysical Observatory in Canada, Oguri Masamune at Chiba University in Japan and Mike Hudson at the University of Waterloo in Canada.

By observing more than one-third of the observable sky outside the Milky Way, Euclid will image billions of targets out to a distance of 10 billion light years. Astronomers estimate the distances to these galaxies — and thus convert two-dimensional images to a 3-D map of the universe — using their observed brightness in different color filters. The more filters used, the better the distance estimate.

Because Euclid is mapping such a huge swath of sky, and ground-based telescopes have different capabilities, multiple observatories have to contribute to provide all the data.

“Pan-STARRS has been mapping the sky for over a decade to search for asteroids for NASA’s Planetary Defense Coordination Office. Leveraging some of this data allows us to provide vital, very deep observations in a red filter that Euclid doesn’t have on board,” explained Chambers, principal investigator of the Pan-STARRS project. “With [the Institute for Astronomy’s] access to Subaru on Maunakea, and working with our colleague Mike Hudson in Canada, we’ve dedicated a large portion of our observing time to adding images taken in a green filter.”

The idea for one filter from space and additional filters from ground-based telescopes was the Euclid plan from the beginning, according to professor Satoshi Miyazaki, director of the Subaru Telescope.

“Subaru observations add far-red and green, Pan-STARRS adds red and [Canada-France-Hawai‘i Telescope] adds blue, enhancing the one filter images that Euclid will produce,” Miyazaki said, adding that UNIONS scientists are sharing data not just with Euclid, but to also for research collaborations in Hawai‘i.

Dark matter does not emit light like the more familiar planets, stars and galaxies. However, they mysterious substance has gravity and can be detected by observing large clusters of galaxies. In some cases, the immense gravity of a galaxy or cluster of galaxies can bend light from an object behind it, known as gravitational lensing. Ground-based observations will also assist astronomers working on the Euclid gravitational lensing project.

“I have worked on the Euclid mission for 12 years and it is very satisfying to see the mission launch,” said Jean-Gabriel Cuby, executive director of Canada-France-Hawai‘i Telescope and Euclid mission board member. “Much like with the James Webb Space Telescope, Euclid will surprise us and lead to insights we do not fully anticipate. Insights enabled by the efforts of the teams at [Canada-France-Hawai’i Telescope], Subaru and Pan-STARRS.”

The Euclid mission will spend more than six years in space and involve more than 2,000 scientists, including astronomers in Hawaiʻi. The Institute for Astronomy team is especially interested in using the data collected to measure the parameters that characterize the properties of the universe.

“The Euclid mission will provide a next generation measurement of these characteristics and we may discover we have made a mistake or series of small mistakes along the way, or we may find that dark energy is more complicated than in Einstein’s formulation. Or there might be something else, some new aspect of the universe that we are presently unaware of,” Chambers said.

The first images from the Euclid mission are expected in about two months.

Euclid will build up a large archive of unique data, unprecedented by volume for a space-based mission, enabling research across all disciplines in astronomy. The data will be archived at the Canadian Astronomy Data Centre and accessible to astronomers around the world.

“The Euclid images will be beautiful to look at, above and beyond the considerable scientific value of the data. I’m looking forward to seeing them,” said Stephen Gwyn, science data specialist at the Canadian Astronomy Data Centre.