Back in 1998, researchers studying supernovae discovered that our universe is accelerating apart. Up until that point, it had been understood that our universe’s expansion was either going to slow to a stop, continue on as is-ish, or reverse it’s motion and collapse in on itself. The idea that it could be accelerating apart wasn’t even on the list because it would require some new something to exist that is causing the acceleration, and as so often happens, our creativity failed to account for the diversity of things at play in shaping our cosmos.
Following our tradition of bad names, astronomers named the unknown thing that is accelerating our universe apart Dark Energy – even though it may not be an energy – and for the past 25 some odd years we;’ve been trying to define what dark energy could be and how it can be observed.
And 25 years is just enough time for major missions and telescopes designed specifically to tackle this question to be coming online. The big three on our radar are the Euclid Space Telescope from ESA, the Rubin Observatory being built in Chile, and NASA’s Roman Space Telescope.
The Euclid mission was the first of this trio to get eyes on the skies. Launching July 1, 2023, it spent it’s first 30 days traveling out the Lagrange point 2, a gravitational sweet point beyond Earth where it will orbit the Sun at the same rate we do. This is the same place where JWST and Gaia space telescope. Once in its final location, it began de-icing procedures and calibration, with the first science images being released in May of this year. Those 5 images, while visually stunning, did nothing to help us understand our cosmos. To complete its primary science mission, the Euclid mission will need to image ⅓ of the sky and carefully measure the shapes and distances to myriad galaxies located within about 10 billion light years of earth. This data will tell us 2 key things:
- By mapping the distribution of objects over time, Euclid will reveal how the large scale structure of our universe has evolved from a spongy material to the lacy web we see today,
- By measuring how the shapes of galaxies appear distorted by the gravity of otherwise invisible dark matter, Euclid will map the 3-dimensional distribution of dark matter.
Putting these two factors together – where dark matter is located and how the distribution of matter changes over time – we can piece together a more complete understanding of what forces must be working on visible and dark matter across time and start to understand if dark energy has always existed and always affected the universe in roughly the same way.
Euclid will spend 6 years acquiring this data. On October 15, Euclid gave us a sneak peak of what is to come. In a data release that showed us roughly 0.5% of the sky in exquisite detail, Euclid was able to reveal the faint clouds of gas that surround or Milky Way as well as myriad galaxies, clusters, and all structures they form together. In the coming months, we can look forward to early analysis of what this amazing data set tells about the universe.
If you want to learn more about Euclid, our sister show Astronomy Cast just did an entire episode on this mission. Check it out at astronomycast.com or wherever you download podcasts.
Euclid will be focusing its cameras on the parts of the southern hemisphere sky that aren’t contaminated by the dust and stars of the disk of our Milky Way. This means it’s observable region overlaps with what will be targeted by the upcoming Rubin telescopes Large Survey of Space and Time. In this complementary investigation, the still-under-construction ground-based telescope will be observing the entire visible sky every few days from its perch in the mountains of Chile’s Atacama desert. This will allow it to not only measure the cosmic structure, but to also catch all the motions of objects in our solar system and the flickers and flares of objects ranging from forming stars to merging black holes.
With science operations slated to start in late 2025, we’re finally starting to see major components of this 8.4 meter telescope and its suite of cameras coming together. The 3.5 meter secondary mirror was installed in July, and on October 28, we learned that a test camera allowed the telescope to finally catch some photons, with first light taking place on October 25. The test camera has 144 megapixels which may sound huge, but the planned survey camera will measure in at 3200 megapixels!. This camera will allow them to put the optics through their paces and to work out any issues in the system before the survey camera is installed in January.
Also experiencing final construction is the Roman Space Telescope. Set for launch in in late 2026 or early 2027, infrared telescope will join Euclid at the L2 Lagrange point, where it will perform complementary observations to Euclid, and also make observations of planets orbiting nearby stars.
Exoplanet observations are made possible by the first ever active coronograph to be sent to space. This means that it will have the capacity to block the light from stars with variable characteristics and can respond to changing conditions to allow different planets to be observed without their star’s light drowning them out. This instrument was integrated into the Roman Space Telescope’s instrument carrier in October and will be mounted into the spacecraft at a later date.
The Roman Telescope will observe the sky in the Infrared, and like the JWST, this is being made possible thanks to some special structures that like to cast shade.
Also in October, we learned that the spacecraft’s Outer Barrel Assembly, which is essentially a long box, has successfully gone through centrifuge testing and is ready for its role-preventing stray light from interfering with observations… or it will be once it too is installed on the spacecraft. Roman still has a ways to go in its construction, but each new milestone gets us that much closer.
And maybe… if we’re lucky, as these surveys wrap up in the 2030s, we’ll start to get a handle on what is pushing our universe apart.