Imagine a telescope–big, heavy, full of a complex array of sensors, dish pointed toward the heavens. While most of these instruments likely have this kind of design, one giant telescope located in the South African desert takes a more DIY approach. Its antennas, each of which measure about 46 feet across, sit directly on the ground. Instead of metal plates, the dish is made of wire mesh. Rather than a hulking base, its support structure is built from wood and PVC pipe. The telescope’s designers built the first prototype with materials you can buy at Home Depot. But this low-fi telescope is providing insight about a far-off scientific phenomenon–the universe’s first stars, which shone 13 billion years ago.
“It’s a funny combo of this high-tech signal processing and computing with what look like really low-tech dishes built out of two materials,” says Aaron Parsons, the principal investigator of the Hydrogen Epoch of Reionization Array (HERA) telescope project and a professor at UC Berkeley. But while the telescope may look hacked together, there is a supercomputer at its center that combines all the data collected by the antennas that’s hidden in a chilled, air-conditioned room.
The supercomputer that powers the HERA telescope is so powerful that Parsons says it is processing an amount of data tantamount to approximately 3% of the total bandwidth of the internet at any given time. So while the supercomputer whirs away, why does the rest of the telescope have such simple infrastructure?
“Some of our insights allowed us to cut some corners,” Parsons says, which enabled them to do a project that was estimated to cost $60 million to one that will only cost $16 million–a tiny amount in the world of science funding. “We’re just in an environment where science is hard to fund. You need to find a way that’s good enough for what you’re trying to do, but isn’t over-engineered.”
Once fully built, the telescope will help provide answers to questions about what caused the first objects to form after the Big Bang and what their life span looked like. One of the key discoveries so far in the project has been how to actually design the telescope in the most effective way to measure the light emitted by hydrogen atoms from the universe’s first stars. Parsons says the two most important criteria in building an instrument that can measure that light is sensitivity and accuracy. The bigger the telescope, the more sensitive it is, and the better able it is to capture the faint light reaching Earth from 13 billion years ago. Accuracy is important because the researchers believed that measuring in great detail was the best way to filter out the other light the telescope captures to discover evidence from the first stars.
In the first design attempting to measure this ancient light, Parsons and his team put equal emphasis on both sensitivity and accuracy. But they soon discovered that sensitivity was far more important than accuracy. The universe is expanding and is 10 times bigger now than it was 13 billion years ago. The wavelength of light also expands along with the universe, so any wavelengths arriving at Earth from 13 billion years ago will be 10 times longer than wavelengths of light from the recent past. Focusing on different wavelengths can be used to see different distances back in time. The team realized that as long as they designed the telescope to prioritize the discrepancies in the wavelengths rather than trying to capture everything at high accuracy, they would be able to discriminate between the long wavelengths from the early universe, while the short, interfering wavelengths from nearby galaxies would appear as nothing more than celestial noise.
“We repurposed all aspects of the design in service of one metric,” Parsons says. The result was the HERA telescope, where each dish measures about 46 feet across with a surface area of about 574 square feet. Currently, there are 19 antennas built, and the team recently received the $15.5 million in funding, which will enable them to build a total of 350 antennas over the next four years.
In order to measure wavelengths using a radio telescope like HERA, the telescope needs to have a metallic surface every tenth of a wavelength. To measure wavelengths that are two meters long–far longer than the wavelengths most radioastronomers measure–the researchers could use wire mesh instead of the metal plates that line the exterior of many telescopes. Parsons compared it to the screen on your microwave: Microwaves are bigger than the holes in the screen, so they reflect off the door, while regular light can pass through.
Mesh is not only significantly cheaper than solid metal, it’s also lighter. This has meant that team can use materials like wood and PVC pipe to support the mesh dishes because they are inexpensive and plentiful.
Still, when Parsons and his team built their prototype made of things you can buy in bulk at Home Depot, they weren’t considering the availability of materials in South Africa, where the telescope is located. So when their local partners began building on the ground, the team had to adjust its design to accommodate different standardized sizes of wood, the smaller abundance of PVC pipes (which are all blue in South Africa), and the availability of a construction support easily found in the U.S. that did not exist in the country.
Not only are they using cheap, local materials–and local labor–the team is recycling technology that was used in the previous iteration of the project. And since the telescope is purpose-built for the experiment, they aren’t as worried about longevity. “We might end up using this telescope for other things, but it’s for the measurement we’re trying to do–finding the first stars,” Parsons says. “We need it to last for five or so years. That also informs the kinds of materials you end up wanting to use. PVC and wood, which degrade when you leave them out in the sun for years, are still viable building materials.”
For Parsons, the HERA telescope is the perfect marriage of practical, hands-on building and advanced technology.
“I grew up on a farm in western Colorado,” he says. “There, when you gotta put up a fence, you drill holes, you put in posts, you stretch wire between them. I like that these kinds of projects are this funny combo of amazing cosmology and science of the first stars and supercomputers, and digging holes and putting in telephone poles.”