Unveiling Secrets of the Universe
The Vera Rubin Observatory is set to begin its first mission: to scan the skies for cosmic events and objects. Its enormous camera will enable scientists to investigate cosmic phenomena on a scale–and at a resolution–previously unseen. Three particular phenomena of interest to the Observatory will be dark matter, dark energy, and Type Ia supernovae. For the next ten years, the Observatory will perform regular scans of the skies, looking for these and other objects and events. The Rubin Observatory plans to begin its survey, the Legacy Survey of Space and Time, in late 2025, and will release its first data set 12 to 14 months later.
The Legacy of Vera Rubin
The evidence for dark matter, an invisible and still-hypothetical form of matter that doesn’t interact with light or other types of electromagnetic radiation, was discovered by Vera Rubin, the American astronomer for whom the observatory is named. Rubin’s calculations of the angular rotation of spiral galaxies showed a discrepancy in the predicted motion of the galaxies based on visible light and observed motion–a discrepancy that could only be explained by the existence of five to ten times more mass than could be seen. This unseen mass was called dark matter.
The New York Times described Rubin’s legacy as “ushering in a Copernican-scale change in cosmological theory.” In addition, Rubin was a tireless advocate for the advancement of women in science, and a mentor to many aspiring female astronomers.
Supernovae, Dark Matter, and Dark Energy
The Rubin Observatory, funded by the US National Science Foundation and the US Department of Energy, boasts the largest digital camera ever built, at 3,200 megapixels, which will allow scientists to capture images in previously unmatched breadth and depth. The Observatory will use gravitational lensing to investigate dark matter. Gravitational lensing looks at the distortion of light travelling from distant galaxies to Earth.This distortion is caused when the light encounters dark matter. By measuring this distortion, astronomers can map the distribution of dark matter.
The Rubin Observatory will also be on the lookout for Type Ia supernovae, which themselves figured into the discovery of dark energy. Type Ia supernovae occur in binary star systems, that is, where two stars–a white dwarf and a second star of a different type– orbit one another. It’s predicted that the Observatory will reveal a much larger set of Type Ia supernovae than is currently known. This, in turn, will help scientists to refine our existing map of space and time, building on the work of the Hubble Space Telescope and the James Webb Space Telescope.
Narrow-field telescopes like Hubble and Webb observe galaxies at very high magnification.The Rubin will observe billions of galaxies, creating the largest galaxy survey in existence. This will be accomplished with the Rubin’s Simonyi telescope, which has the largest focal plane ever built for astronomy.
The telescope is designed to reorient its gaze every 34 seconds. As a result, astronomers will be able to scan the entire sky every three nights. Over the course of the ten-year survey, Rubin will observe each galaxy 800 times, enabling scientists to measure the distortion of the galaxies with greater precision. This, in turn, will allow them to map dark matter.
“That’s the power of Rubin,” Steven Ritz told The MIT Technology Review. Ritz is a Rubin project scientist at the University of California, Santa Cruz. “The sheer grasp of being able to see the universe in detail and on repeat.”
In addition to mapping dark matter, scientists plan to examine its behavior. Currently, the leading idea, the cold dark matter model, holds that dark matter moves more slowly than the speed of light and interacts with ordinary matter only through gravity.There are other models, however, which suggest different behavior. By comparing maps of dark matter with the predictions of these models, scientists could exclude some theories in favor of others.
Rubin scientists will also use gravitational lensing to study dark energy. Andrés Alejandro Plazas Malagón, Rubin operations scientist at SLAC National Laboratory, describes dark energy as the flipside of dark matter. Dark matter pulls matter together, while dark energy pushes it apart. Dark energy was theorised to explain the accelerating expansion of the universe observed by scientists in the late 1990s. Type Ia supernovae act as “standard candles,” meaning astronomers can measure their brightness to gauge distance. Combining this with a measure of how fast they’re moving, astronomers can discriminate between theories about how the universe is expanding.
The maps of dark matter that will be created using Rubin’s data will also allow scientists to plot out how the structure of the universe has changed over time.
By the Numbers
According to the Rubin team, the Observatory generates some 20 terabytes of data–that’s three years of continuously streaming Netflix–every 24 hours. After the current ten-year mission, the Rubin will have generated 60 petabytes of raw image data. This is equivalent to 500 times the data gathered by the Hubble Telescope in its lifetime, or one million times the data contained in Wikipedia.
This data is predicted to include:
20 billion galaxies
17 billion stars
10 million supernovae
6 million solar system objects.
From this data, Rubin will generate a public stream of some 10 million alerts every night–alerts that will be distributed to community brokers, that is, software systems that will ingest and process the alerts, then serve them to the broader scientific community.
Four Goals
The Rubin Observatory has set forth four ambitious goals for the Legacy Survey of Space and Time: understanding the nature of dark matter and dark energy, creating an inventory of the Solar System, exploring objects that change position or brightness over time, and creating a map of the Milky Way. These accomplishments will help us to better understand not only the makeup of the universe, but its history, and where it might be headed.