Tuesday, April 16, 2019 1:00 am
Wonder of discovery
Black hole offers vivid demonstration of rewards of scientific pursuit
Last week the first image of a black hole was released. I had been following the team's progress for the past several years, so I was excited to see their work finally pay off. It was especially nice to see a picture bounce around the internet of Katie Bouman, the scientist who led the computer algorithms required. The picture of Bouman showed the moment the team discovered the project had been successful.
The fundamental difficulty with taking an image of a black hole is that black holes appear small. The black hole the team concentrated on, at the center of galaxy M87, is the second-largest black hole, in apparent size from Earth, in existence.
The scientists needed to get the best resolution possible. A decades-old method in astronomy for getting better resolution is to use several telescopes together. A typical telescope works by a mirror reflecting light into a focused image. One key to a focused image is that light that hits each part of the mirror arrives at the image in the same amount of time. If the light doesn't arrive in the same amount of time, the image will not be in focus.
To recreate this process with several telescopes requires using radio waves instead of standard visible light. Next, the scientists need a way of measuring the waves at each telescope then afterward combining the radio waves from the different telescopes together.
One key here is that they want to combine the radio waves from the different telescopes that arrived at the same time, but not the radio waves from different times. Even a nanosecond of difference (literally a billionth of a second) makes a big difference.
That requires the radio waves to be measured with extremely accurate times. Just recording the total radio wave brightness was not sufficient. The scientists needed to record the radio waves at each fraction of a second and have all the telescope clocks in sync with one another.
That meant recording a lot of data. The data at each telescope was produced at a speed about 1,000 times faster than a typical high-speed internet connection.
None of the hardware to solve these problems existed at the telescopes. The team of scientists had to build the equipment, go to the telescopes to install it, make sure it worked, then start the actual astronomy observations.
Did I mention one of the telescopes was at the South Pole?
I was surprised by when the telescopes were used to observe the black hole. Two years ago! The scientists have been working for two years to convert the observations into a reliable image.
The fundamental problem with this part of the project is that, because of random noise in the measurements, there are multiple images that are almost equally consistent with the data. The scientists can use their expectations of what the random noise can typically do to pick out the best image.
They had to be careful, however, to avoid choosing the image that simply fit their preconceptions of what a black hole should look like. This balance, of using some preconceptions but not others, is delicate.
One of the innovations that Bouman led was to develop more reliable methods for hitting the right balance than had been done previously.
The picture of Bouman at her computer is apparently when they first applied their carefully designed computer program to the actual data to construct the image. The clear joy in that result is a great demonstration of the excitement of scientific discovery.
It is sometimes hard to convey to those outside of the field why practicing science can be so attractive. This discovery demonstrates it, though. Nature is a certain way. Those ways are discoverable. That discovery can be joyful.
Christer Watson, of Fort Wayne, is a professor of physics at Manchester University. Opinions expressed are his own. He wrote this column for The Journal Gazette, where his columns normally appear the first and third Tuesday of each month.