by S. Prasad Ganti

In the Andes mountains in Chile, a new telescope has captured the first light and produced the first pictures. It is exciting new technology. The pictures are equally exciting as well. Whenever a new telescope comes up, either on the earth and in space, a question comes to my mind as to how is this telescope different from others ? Is it just technology to make pictures sharper or does it represent a whole different paradigm shift ? Rubin Telescope is clearly defining a new paradigm in observation and data capture.

The Rubin Telescope is named for astronomer Vera Rubin who contributed significantly to the area of dark matter. The primary mirror itself is not larger than any of the existing telescopes. At 8.4 meters wide, the captured light is focused on to the most powerful camera ever built. The camera is the size of a small car and its CCD (Charge Couple Device) based sensors can capture 3.2 giga pixels (or 3.2 billion pixels or picture elements) in one shot.

Rubin is very maneuverable to swing around the sky to take shots of different locations every 40 seconds. To reduce the weight, a small portion of the primary mirror acts as a tertiary mirror. The picture given below, courtesy NSF-DOE, shows the optical design of the telescope. Light is coming from top to the primary mirror at the bottom. The reflected light goes to the secondary mirror at the top. The light then bounces back to a small area of the primary mirror called the tertiary mirror. Next it bounces to the middle of the picture to be caught by the CCD sensors.

The location in the Andes mountains is very remote and away from the main electric grid. The energy required to start and stop the telescope is stored in electrical capacitors and then quickly released again, a similar principle to storing solar and wind energy in batteries and then using it later. 

Rubin scans the whole sky every three days. It comes back to the same location in the next cycle. The stars do not change, but the planets and asteroids do move. For the objects which do not move, the second picture reinforces the first picture taken three days earlier. A cumulative image of the distant objects gets built in each cycle in a process called “coadding”. By the end of Rubin’s ten year lifespan, the coadding process will generate images with as much detail as a typical Hubble image, but over the entire southern sky. And in frequencies including near infrared, visible and ultraviolet ranges. 

The path the telescope takes to scan the sky each night is fixed each night over its expected ten year lifespan. There is no catering to individual astronomical studies like it is done for other telescopes where astronomers request for time to point the telescope to a specific object. Instead all the astronomers the world over will have the opportunity to study the huge amounts of data already collected by the Telescope. 

The extraordinary amount of data collected (20 tera bytes each night) poses an information technology challenge. A 600-gigabit fiber connection has been laid from the mountain to La Serena, the closest town. From there, a dedicated 100-gigabit line and a backup 40-gigabit line connect to the Department of Energy’s network in the US. The computers at SLAC (Stanford Linear Accelerator Center) will process this data by filtering out all the streaks produced by passing satellites and smudges generated by cosmic rays hitting the camera sensors. Then the software will compare the scene with a template that combines at least three earlier observations of the same part of the sky. The processed data is made available to nine outside organizations known as data brokers. These automated software systems will perform additional analysis, pull out data of interest to astronomers all over the world. It will also identify interesting events that require follow-up observations by other telescopes. 

Earlier, Vera Rubin discovered that the outer parts of galaxies are rotating too fast to be accounted for by the visible matter. It is suspected that “dark matter” exists as outer halos around the galaxies. The Rubin Telescope will study dark matter using a technique called “gravitational lensing”. As light from distant galaxies travels to earth, the light bends (as per Einstein’s General theory of relativity) due to the dark matter on the way. By measuring how much the light is bent, astronomers can create a map of dark matter’s distribution. 

Another “dark” twin is the dark energy which indicates how fast our universe is expanding. Rubin will study dark energy with high-resolution glimpses of Type Ia supernovas. These are standard candles which show how far a galaxy is from us. By determining the red shift (shifting of the light towards lower frequencies as the source receedes away from us) of each standard candle, we get a measure of the dark energy which is driving our universe apart. 

One of the  first pictures, courtesy NSF-DOE,  is shown below. It contains the Virgo cluster of galaxies, including two spiral galaxies (lower right) and three merging galaxies (upper right). 

We are capturing so much light to study the “dark” secrets of our universe. The extra-ordinary camera and the unprecedented computer and communications network make Rubin very valuable for astronomers all over the world. As one astronomer mentioned, we are entering the era of “astro-cinematography”. The telescope was funded by the National Science Foundation (NSF) and Department of Energy (DOE). Will the name of the Telescope and the funding for day to day operations survive the current political climate ?