Astronomy is on the brink of opening an “unprecedented window on the universe,” generating so much information about the ever-changing night skies that scientists will be challenged to handle the intense stream of information being collected.
The telescope that will generate the information, called the Large Synoptic Survey Telescope, is now being assembled on Cerro Pachon, a 8,800-foot mountain ridge in Chile.
Starting next year, it will be the focus of a kind of astronomy that is a far cry from the traditional concept of a lonely star-gazer peering through a long telescope at a distant galaxy, according to William Dawson, a Lawrence Livermore National Laboratory physicist.
Astronomers will indeed use the new telescope’s findings, he said, but they won’t do so in a darkened observatory.
Instead, they will sit at their desks in astronomy departments around the world, receiving such an intense stream of information over fiber optic cable that it will be a major challenge to separate what they need to know from what they do not.
After initial operations next year, LSST will be ramped up to full operation in 2022. As Dawson described it, the 8.4 meter telescope will generate a “multicolor time-resolved faint sky map” that reveals what is changing and what is not, night after night, among “20 billion galaxies and 20 billion stars.”
Emphases are simultaneously on the word “faint,” meaning faraway and hard to see, and also on the idea of the entire, constantly changing sky, not just a single star or galaxy for an hour or two.
Every Two Nights
Every patch of the sky will be imaged every two nights, Dawson said. Astronomers will be able to examine enormously detailed time-lapse recordings to search for phenomena they are interested in, from supernovae to near Earth objects.
The 20 billion stars are those of our own Milky Way galaxy, constituting nearly all of what we see at night with the unaided eye. The 20 billion galaxies fade off into the celestial distance, many of them a challenge to view even with powerful ordinary telescopes.
In stargazing, great distance corresponds to the passage of time.
Dawson said that the LSST will look so deep into the sky that it will see back to the time when primordial galaxies overlapped one another in a celestial blur. This is around 100 million years after the universe as we know it blossomed out in the so-called “Big Bang.”
He showed slides comparing detailed observation of the same patch of sky by the Sloane Digital Sky Survey, which began in 2000, with that anticipated from LSST in coming years.
The Sloan survey has produced an abundance of high quality research, yet LSST results are expected to be far more detailed.
One of Dawson’s personal scientific interests will be in images of distant galaxies that appear to brighten and then dim.
These might reveal the passage of an otherwise unobserved black hole whose gravitational field temporarily focuses light headed towards Earth.
If enough black holes could be found, they might provide at least a partial explanation for one of astronomy's current mysteries, the nature of “dark matter” that seems to constitute some 85 percent of the universe.
Ordinarily, telescopes have either looked deep but narrowly into space – sometimes called the soda-straw view – or with a wide angle.
Revolutionary advances in technology, some of them contributed by LLNL, will enable the LSST to do both. It will scan the skies with a 3.5-degree view, seven times the width of the moon as seen from Earth.
For comparison, the Gemini Observatory has twin 8.1-meter telescopes with a much narrower 0.2-degree field of view. These are located in Hawaii and in Chile near the LSST site.
“With 20 billion galaxies and 20 billion stars all in color, (LSST) is much more than a traditional telescope,” Dawson said.
New Breed of Astronomers
Operation will be “mostly a data analysis challenge,” he continued. “Dealing with this amount of data, processing that, finding a rare object of interest in the vast sea of data, will bring new challenges taking a new breed of astronomers.
“There is so much data that simply processing that data requires a great deal of work.”
Dawson described the LSST and its capabilities last week to a meeting of the Livermore Laboratory Retirees Association.
The project is jointly funded by the U.S. Department of Energy and the National Science Foundation, with private contributions from Charles and Lisa Simonyi and from Bill Gates.
So rich is the flow of information expected to be that the project requires an automated alert system for notifying astronomers of detected changes in the night skies.
The alerts are expected to number in the millions, raising the question of how to identify the most important for immediate further scrutiny.
New statistical techniques are being developed to deal with the data flow, Dawson said.
Another feature of LSST operations will be an active public outreach program, making LSST data available to K-12 schools and amateur astronomers.
Innovations from LLNL
Present in the retiree audience was Lynn Seppala, former chief optical designer for LLNL’s laser program, who 20 years ago moved the dream of a telescope with LSST’s capabilities close to reality.
With the encouragement of Kem Cook, an LLNL physicist already associated with the project, Seppala created an innovative three-mirror design that impressed reviewers and gave the potential funding agency, the National Science Foundation, confidence that LSST could be successful.
In an email following the luncheon talk, Seppala called the design effort “enormously complex,” with “many, many iterations” required to create a telescope that would maintain high resolution across a wide field of view.
It was something of a “leap of faith” to propose a revolutionary design involving three mirrors, two of them fabricated on the same piece of glass, he said.
The telescope had to account for six color ranges, greatly increasing the difficulty compared to designing a laser system that emits light at a single wavelength.
The result was a relatively compact design – as compact as an 8.4-meter telescope can be – that can pivot rapidly to view a new part of the night sky, settle into stability and start making observations quickly compared with more elongated designs.
The three-mirror assembly will reflect light into LSST’s digital camera, the largest ever built. Roughly the size of a small car and weighing more than three tons, it will have 189 16-megapixel detectors and will collect so much light that heat control is a serious issue.
As the time approaches for the LSST to see “first light,” Dawson said he is “very excited.”
In fact, he thinks “we should all be excited… This will be the greatest survey that man has ever made of the universe.”