The vast majority of telescopes today observe just one small part of the sky at a time. In order to obtain data about a specific star, black hole, or other celestial object, researchers must request a telescope be pointed in its direction. At least, that’s how things used to be. With the ground-breaking Vera C. Rubin Observatory in Chile, many scientists will be able to study all different parts of the observable universe at once.
Rubin’s telescope, located on Cerro Pachón in the Andes mountains, is designed to move remarkably quickly; it’s able to photograph the entire night sky every three to four nights, making it 10-100 times faster than other comparable telescopes. Its vast size and speed allow researchers studying entirely unrelated topics to share the same data set, as that set contains virtually everything.
Over the next 10 years, starting in late 2025, the Vera Rubin Observatory will be taking pictures of the Southern Hemisphere sky every night with no breaks. This forms part of the Legacy Survey of Space and Time program (LSST). LSST will be the most comprehensive survey ever conducted on space. In its first year, it will collect more data than all other observatories in history combined. Besides discovering millions of asteroids, billions of galaxies, and deepening our understanding of dark energy and dark matter, the survey will allow scientists to put together a years-long time-lapse movie of the universe, giving insight into how it has evolved and will continue to change.
Every night of LSST, the telescope’s digital camera–the largest in the world–will take around 800 panoramic photos of the southern sky. Each time a change is detected in an image, an alert is created with a unique identifier and information about the change. Some of these changes may include transient astronomical events like supernovae, variable stars (stars that vary in brightness), and fast-moving objects like asteroids that change position between pictures. On average, every new LSST image produces about 10,000 alerts, and it’s expected to generate approximately 10 million alerts per night. This is a staggering amount, six petabytes a year in image data and 60 petabytes after the survey is complete. To put this into perspective, the average HD movie is about 5 gigabytes; you would have to watch movies for 1,370 years nonstop to consume that amount of data.
The Vera Rubin Observatory isn’t going to be processing all of this data locally, though. Instead, the image data acquired at the observatory in Chile will be sent to the US Data Facility at SLAC National Accelerator Laboratory in California, which will generate alerts within 60 seconds of the image being taken. To create the alerts, LSST’s Prompt Processing system performs Difference Image Analysis, meaning it compares the new image to an older reference image to find any objects that changed or moved. Then, it detects and measures characteristics of sources in the difference image before finally generating the alert packets, providing real-time updates for researchers. This is crucial for time-domain astronomy, which studies how objects in space change over time.
Rather than allow access to the full stream of LSST alerts to individual users, the distribution of alerts will be managed by third-party alert brokers at the LSST Archive Center in Champaign, Illinois. Alert brokers are software systems that process alerts and make them accessible to scientists. Researchers can access and analyze data from LSST in a more organized format through the broker’s interface. It allows them to filter and sort the alert stream, as well as providing context for astronomical events (like supernovas) or comparing with existing archives. Scientists looking to conduct alert-based research will be able to choose brokers based on their needs.
For LSST, there are both “full-stream” brokers, which receive and process the entire LSST alert stream, and “down-stream” brokers that process already-filtered data. For example, the Solar System Notification Alert Processing System (SNAPS) broker is a down-stream broker that provides information about objects within our solar system; its focus doesn’t require access to the entire stream. A subset of the alert stream will also be available through the Rubin Science Platform (RSP), an online service, and there will be community filters that serve a variety of goals and will be open to anyone.
In addition to the millions of alerts generated daily, LSST will also supply annual data releases on the RSP. Unlike the alerts, which are primarily about temporary and quickly moving objects in space, the releases will be more thorough analyses of long-term trends and slower-moving objects like stars and galaxies. These data products include catalogues and coadds, images made up of many photographs consolidated into one.
The Vera Rubin Observatory is expected to help scientists make monumental discoveries in astronomy in the next 10 years. With the massive amount of data and images that will be made available through LSST, it serves to make science more accessible to everyone.
Acknowledgements:
A big “Thank you” goes to Michael Wang (Fermilab) and Yatish Kumar (ESnet) for providing pointers to important details on the Vera Rubin telescope.
Learn more about research opportunities in this field: http://www.cs.iit.edu/~nsultana1/student_projects/phd.html
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