Lockman’s discovery resonates three decades later

Suzanne Stewart
Staff Writer

People who create, discover and learn are motivated by different things. In the 1980s, Green Bank Observatory principle scientist Jay Lockman was motivated to prove someone wrong. This motivation led to a discovery which was named for him, with a publication and a Wikipedia page dedicated to his discovery.

“It’s a funny thing – it’s a little complicated – but basically I heard someone give a talk, this would have been 1980, maybe even earlier – where he said ‘wherever you look in the sky, you see hydrogen in the Milky Way,’ and I thought, ‘I wonder if that’s really true?’” Lockman said.

At the time, all the telescopes at the National Radio Astronomy Observatory had legs and Lockman realized those legs were causing a unique type of interference which may have led to the belief that hydrogen was seen everywhere in the Milky Way.

“You know how most dishes have legs in the front of them?” Lockman began. “You can get radio waves scattering off the legs that would actually mask a small hole in the sky. It’s very much like if you’re looking through a rainy windshield at night. You can look at an area where there is no light, but if you have light off to the side, it can scatter it in.

“There’s a thing that happens with normally designed radio telescopes – they can have scattered radio waves, so you could be looking at a place where there’s nothing and, in fact, get some signal, but the signal is coming from off to the side,” he continued.

“I was aware of this for a long time, and I thought, ‘I bet you that could hide a real hole in hydrogen’ and then the question was, ‘how can I correct for this effect?’”

Lockman’s discovery that telescope legs could cause interference and bounce radio waves was taken into consideration when the Green Bank Telescope was designed. The GBT doesn’t have legs in front of it, so there is a reduction in scattering.

But that’s not the discovery named for Lockman. The story continues.

Lockman was teamed up with a graduate student and an advisor from the University of Wisconsin, and they worked on a way to reduce the scattered signal issue associated with telescopes that have legs. They used the 140-foot telescope for the projects.

“It was a series of projects involving x-rays and other things, and one of them was looking for a hole,” Lockman said. “We were looking for a hole. I wanted to do it just to see if I could prove this guy wrong, and it’d be fun to find.

“It turns out it was important because x-rays from way out – like quasars, very distant things – get blocked by hydrogen in the Milky Way, so, in some sense, if you find a place with the least hydrogen, that’s where you can look out the farthest.”

The team found that place in the Milky Way. It wasn’t completely devoid of hydrogen, but the numbers were low and that was the discovery that became known as the Lockman Hole.

“We found a place,” he said. “It didn’t have complete zero, but it was the lowest in the sky. We published a paper, and I was the first author on that. We had a series of papers because the other work on the x-ray properties of the sky and things got the guy his PhD thesis.”

The Lockman hole – named by Lockman’s friend in Wisconsin – has been used in several projects around the world, including one in Germany.

“There was a German satellite going up to look at x-rays, and they wanted to pick a spot in the sky to study for hundreds of hours,” Lockman said. “They wanted to look at the place with the least hydrogen, and they picked the place that we had found.”

While the discovery is called a hole, Lockman said it’s technically more of a window.

“On a contour map, it looks like a hole,” he said. “It’s not exactly a black hole. It is a window. A black hole is something that can have as much matter as the sun or a thousand or a billion suns in a small place.

“It has nothing whatsoever to do with this thing that got named the Lockman Hole,” he continued. “We have people at Green Bank who study black holes, but they are really something totally different.”

Although he was able to prove the individual wrong, Lockman said at first he was disappointed with the discovery.

“The thing was, when I found it, I was disappointed because the signal didn’t go to zero,” he said. “I thought, ‘well, this is interesting,’ but I didn’t realize it’s importance to other people. There’s a Lockman Hole project going on in Europe now to do a lot of coordinated observations of it.”

A simple motivation to prove someone wrong led not only to a discovery, but to a piece of the Milky Way that is still being observed by others. And it led to more know-how on ways to improve instruments used to survey the night sky.

“The technical issues that got me interested in it and that we had to overcome to make the measurements, contributed to the design of the GBT,” Lockman said. “The GBT has a much better performance for this kind of thing than any other big telescope, because we have just the one arm off to the side and not the blockages, as it’s called.

“It really has a resonance there.”

More than three decades later, the Lockman Hole continues to prove its worth for astronomers around the world – a fact its namesake doesn’t let go to his head.

“I’m working on other parts of the Milky Way and things like that, so this is just something from my past,” he said. “It’s kind of humbling.”

more recommended stories