What To Know
- when we observe a light source through a “lens galaxy,” we do not see a single image, but several distorted images, arranged in a luminous halo called an “Einstein ring.
- The images of Einstein rings obtained using the new gravitational lenses will also allow the Université de Montréal team to estimate the expansion rate of the Universe, a very hot topic in cosmology.
- Dark energy, the force that accelerates the expansion of the cosmos, will be studied by other teams thanks to the many supernovas that will be detected by the camera – these “candles” make it possible to precisely calculate astronomical distances and therefore….
Here, as elsewhere, research teams are meticulously preparing for the commissioning of the Vera C. Rubin Observatory, scheduled for 2025.
On the crest of Cerro Pachón in Chile, you can now admire the imposing silhouette of the American Vera C. Rubin Observatory. Planned in 1996, its construction began in 2015 and will only be completed this year. This observatory will have required several technical feats, including the manufacture of the largest and most sensitive astronomical camera ever built! The size of a small car, it will be able to detect with its 3.2 billion pixels a wide spectrum of wavelengths, ranging from ultraviolet to infrared. Initially named LSST (Large Synoptic Survey Telescope), the observatory was finally named Vera C. Rubin in honor of this American astrophysicist who died in 2016, a pioneer in the study of dark matter. It was precisely designed with the aim of lifting the veil on dark matter and dark energy. These, although invisible, are said to make up 96% of the Universe, and remain the greatest mysteries of current astronomy. Even before producing its first images, the observatory is already generating a lot of interest in the scientific community. “It’s extremely exciting!” enthuses Yashar Hezaveh, cosmologist and professor of physics at the Université de Montréal. With his colleagues, including cosmologist Laurence Perreault-Levasseur, he is already hard at work designing methods for analyzing future data. Starting in 2025, the observatory will begin an unprecedented celestial monitoring exercise: Legacy Survey of Space and Time. Every 3 to 4 nights, for a decade, it will produce a complete survey of the sky in the southern hemisphere. Its camera, specially designed to detect objects that change in brightness or position (such as supernovae), will act as a real astral watch. It will emit an alert to signal any changes – more than 10 million are expected per night! “Before, we could follow fairly small objects, like a star or a distant galaxy. But no survey of the sky was available on a large scale,” explains Yashar Hezaveh. Like Vera Rubin before him, this researcher is particularly interested in dark matter, this sort of invisible glue that holds galaxies together. In particular, he hopes to map its distribution to learn more about its fundamental properties. But studying dark matter requires a certain amount of creativity: since it does not interact with light, it is undetectable by our measuring devices. However, we know that it has mass, so it exerts gravitational effects on its surroundings. And these are the effects we are tracking.
The world’s largest astronomical camera has six filters that can be changed automatically five to 15 times a night. Photo: Jacqueline Ramseyer Orrell/SLAC National Accelerator Laboratory
Lens help
So, to map it, we need to observe its effects on light using “gravitational lenses.” These are massive celestial bodies, such as galaxies, whose gravitational field deflects the light emitted by a distant source from its trajectory. Result: when we observe a light source through a “lens galaxy,” we do not see a single image, but several distorted images, arranged in a luminous halo called an “Einstein ring.” However, the dark matter contained in a lens galaxy also exerts a gravitational effect on light. It leaves a very distinct imprint on the Einstein ring, which allows us to deduce its distribution in the galaxy. The problem is that it is very unlikely to find a lens galaxy: the alignment between the light source, the galaxy and the telescope must be perfect. Typically, we have to scan a million galaxies to find a single one. “For the moment, only a few hundred gravitational lenses have been identified. But with this observatory and its recurring surveys, we expect to identify nearly 200,000 of them!” exclaims Yashar Hezaveh. The images of Einstein rings obtained using the new gravitational lenses will also allow the Université de Montréal team to estimate the expansion rate of the Universe, a very hot topic in cosmology. Dark energy, the force that accelerates the expansion of the cosmos, will be studied by other teams thanks to the many supernovas that will be detected by the camera – these “candles” make it possible to precisely calculate astronomical distances and therefore the expansion of the Universe.
The analysis challenge
In order to sift through the mounds of data that will be generated, the Université de Montréal team is already using artificial intelligence (AI). And thanks to Quebec’s expertise in AI, the team is well positioned to perfect the numerical methods needed for the calculations. In ten years, the Vera C. Rubin Observatory is expected to produce 60 petabytes of data (it would take about 70,000 laptops to store it all!). Who knows what such a quantity of information will reveal? “The data will be a bit like a treasure chest for astronomers and cosmologists,” concludes Yashar Hezaveh philosophically. We study [la matière noire]a known unknown. But I believe that the most interesting discoveries will concern unknowns… unknowns!”
Wide view of the telescope mount, inside the dome. Photo: H. Stockebrand/RubinObs/NSF/AURA
