A Short Drive Away, the Largest Steerable Radio Telescope

Feb 4, 2019

Two hours by car west of Harrisonburg, the Green Bank Observatory is home to the world’s largest steerable radio telescope.  This facility owned by the National Science Foundation might be, well, under the radar, but it’s being used for some very forward-thinking projects you might not expect – including a search for extra-terrestrial intelligence. WMRA’s Marguerite Gallorini has more.

It is not easy getting to Green Bank. To reach this small West Virginia town of only 143 residents, you have to wind through mountain roads for about an hour. And suddenly there it is, sitting in the valley: a 500-foot tall radio telescope – the Green Bank Telescope, or “GBT” for short.

The reason this telescope needs to be out of sight, lodged in the middle of the Allegheny Mountains, is to provide a natural barrier against radio interferences from surrounding cities. The GBT is aiming to catch faint radio waves from as far as fourteen million light years away. Sue Ann Heatherly, Senior Education Officer at the Green Bank Observatory, explains how it works:

SUE ANN HEATHERLY: The dish is a mirror. So imagine that, if you're trying to look at stars through a telescope, you're going to point your telescope at a star; that light from the star is going to hit the mirror in your telescope and bounce up into your eye. The same thing happens with the radio telescope - the difference is that our mirror is not very shiny: it is white. And if there are objects out there in the universe that emit radio waves, we can see those radio waves by pointing our dish in the right direction.

That is the specificity of the GBT: it is the world’s largest steerable radio telescope. That means that this seventeen-million pound metallic structure can rotate 360 degrees in only nine minutes, which means it can cover 85% of the sky, while most other radio telescopes are fixed and can’t cover as much sky surface.

And, as sensitive as it is, a simple cell phone could interfere with the signals it is trying to capture. So, besides the mountains, the observatory also benefits from the National Radio Quiet Zone: a 13,000-square-mile national preserve for radio astronomy, which covers a part of West Virginia, Virginia, and Maryland, and where cell phone towers are more regulated. But in Green Bank in particular, there is no cell phone reception at all – a fact that tour guide Rebekah Anderson jokes about:

REBEKAH ANDERSON: When I went to college, where cell phone service – obviously, they're used to it – an ice breaker was always like "What's your name and major, and what's an interesting fact about yourself" and I would always say "I live in a place with no cell phone service" and everybody was just shocked.

More than half of the observatory’s funding comes from the NSF [National Science Foundation], with the rest provided by university or private projects.  One of those funding streams is for a project called Breakthrough Listen, also known as SETI – as in Search for Extra-Terrestrial Intelligence. It takes up 20% of the telescope’s time, looking for signs of alien intelligence.

HEATHERLY: The whole idea of using a radio telescope to search for signals from other civilizations was launched right here in Green Bank in 1960. Over the intervening years, a project would pop up here and there and SETI research would come back to Green Bank – but this is the first one, this Breakthrough Listen project is the first really well-funded systematic search where we don't have to worry about the project being cancelled.

Recently, Heatherly says, the Green Bank Observatory also partnered with NASA on the InSight lander project, which is studying the interior of Mars and listening for Marsquakes.

HEATHERLY: This is a spacecraft that's been travelling toward Mars since May [of 2018], and it had a very tricky landing sequence and it was producing a little signal that the GBT could detect… Sometimes we work with NASA on these things. So we had party – we had a landing party and it's just really exciting and uplifting to see some of the good that's going on, you know, science-wise.

The GBT’s influence is also reflected locally. It’s very important to nearby West Virginia University, where the astronomy department has expanded. Andrew Seymour is a staff scientist at the observatory, and previously studied at WVU. Last year, he took part in the discovery of mysterious bursts of radio emission, called Fast Radio Bursts – “FRBs” for short. Those are the same kinds of signals detected by a Canadian telescope from another part of space just last month.

ANDREW SEYMOUR: When you have a supernova and that explodes, it causes the core to collapse, it gets compressed. So this is basically the last step it can take before it becomes a black hole.

And when it gets compressed, it spins around like a lighthouse – and every time it spins around, there’s a flash of light which the telescope can time very accurately.

SEYMOUR: These objects are actually being used to help discover gravitational waves. It's what we call timing, or when we should expect these pulses to arrive – it could be due to the fact that a gravitational wave came through our galaxy.

Because of the big projects going on in this small West Virginia town, local residents don’t seem to mind being off the grid, for the sake of scientific progress. Donnie Ervin works at Trent’s, a nearby general store, and he says he loves being around the observatory.

DONNIE ERVIN: I like it here. They do some pretty interesting stuff; I love to read the articles whenever they find something new. Growing up around it, it's just part of the community.