By JULIE LAFRANZO
How do you take a picture of a Blackhole? “Well you certainly can’t use a camera,” Herbert said. Schwartz, Astronomical Observatory Lecturer at the Drake Municipal Observatory. The blackhole that was imaged was at the center of galaxy M87, which is approximately 55 million light years from Earth. Blackholes are at the center of all galaxies (that we know of) and scientists believe that they are the size of a star with the mass of millions or billions of stars, for example M87’s blackhole is about 6.5 billion suns. The definition of a blackhole is that it sucks in everything that gets into a certain distance from it, that distance is known as the Event Horizon.
The “image” of the blackhole that was released is actually an “image” of the event horizon around the blackhole. “Image” is in quotes as it is not a visual image, as Schwartz put it. “It is a radio picture, not an optical picture,” Schwartz said . “As people we only deal with a tiny piece of the electromagnetic spectrum. The idea is that if we can get information from other areas, we can ‘see’ an awful lot more. Radio telescopes work in the radio band and the neat thing about that is that the wavelengths are a bit bigger and so they are easier to work with.”
As Schwartz said, our eyes don’t see the entire spectrum of what there is to see and so using other wavelengths, like radio waves, we can “image” things that we wouldn’t have been able to see before, like a blackhole.
“Based on the placement [of the radio waves] they were able to construct an image. That is the image that everyone sees and they say ‘oh there’s the picture, isn’t that a lovely picture.’ No, it is not a picture. It is basically a plot of the energy that we are getting out of a tiny little area. It is a scan of the energy in that area,” Schwartz said. Calling it the first image is not wrong but it would be more correct to call it a radio image as it is not made from visual wavelengths, it’s made from radio wavelengths.
Ken Young, former astronomer who worked on projects like imaging a blackhole, gives insight on how to image a black hole from Earth.
“As the Earth rotates that projected distance and the orientation changes slowly as the Earth rotates and so as the Earth rotates you collect information about different spatial frequencies so at any instance you are measuring the amplitude and phase for one spatial frequency and if you had an infinity number of antennas spread over the Earth and completely sampled all the spatial frequencies, it would be a trivial thing to make an image out of that because all you would have to do is add up all the sine waves on the sky with the correct amplitudes and the correct phase offsets that shifts them around and that would give you your image. The trick is that we don’t have telescopes all over the planet, we have very few telescopes on the planet and so you tremendously under sample the spatial frequencies that you would ideally like to have,” Young said. Young’s explanation and more is how to image something like a blackhole. The Earth is moving and using that to your advantage to get the image that you want. If the Earth had a lot of telescope all over, then we could get images very easily, unfortunately that is not the case. Instead, they are instead using the Earth’s movement to get the image.
“The tricky thing is that if you just take direct image from the spatial frequencies that you have taken, it looks terrible because there is all sorts of information that you haven’t gathered,” Young said. “As the Earth rotates, you’re slowly filling in that dish that you want to have filled.”
That’s how you get the image that you want. All of the telescopes that you do have are filling in the space that you would have with more telescopes as the Earth is moving. This is using the Earth’s rotation to our advantage to find new things to see things that we could have never found before.
Photo courtesy of Jet Propulsion Laboratory
