A Photo of a Black Hole: What’s Next?


I mentioned at the beginning of the year that I never really know what to do about blogging about science news. I don’t really know what to say that hasn’t already been in all the news articles. This week’s first ever photo of a black hole has been a perfect example of that. It’s been really big news for a science story, which I find very encouraging. But that also means it’s that much harder to figure out what to say that isn’t in the news articles. Worse yet, I haven’t actually been paying attention to the news articles because I watched the science press conference on Wednesday, which covered it better. And finally, I’m discovering with this story that I often don’t have time to move quickly enough to put out a blog post in the current news cycle.

So basically, I’m still trying to find my niche with this stuff. I’m not sure where that’s going in general, but I had an idea for this particular story. I want to pivot away from the big news of the first photo of a black hole because if you’re interested enough to be reading this, you probably know all about it already. Instead, I want to turn to something you might not have heard about: what’s coming next. (Some articles have addressed this too, but I think I have more to say on this point.) Because even though they took this photo with a virtual radio telescope as big as the Earth, there’s still room to improve it.

There are actually four different ways to improve upon the technique used to take this image, all of which NASA scientists are planning on using. This means that in a year or two, we could have a significantly better picture of a black hole, and a few years after that, we could have a much better one. Let’s go through them.

1. Observe at a shorter wavelength.

The Event Horizon Telescope (EHT), which took the photo, is a super-array of eight radio telescope arrays in six locations that create a virtual mirror across the Earth. Each of these telescopes can observe at a wide range of wavelengths. The M87 black hole was specifically imaged in extremely high frequency radio waves with a wavelength of 1.3 millimeters. (That’s about 231 GHz.) Now that they know it works, the researchers want to observe at a shorter wavelength of 0.87 millimeters. The sharpness of the image is inversely proportional to the wavelength, so this would make it 50% sharper. That’s a pretty good improvement by itself.

2. Build more radio telescopes.

The EHT has already added another telescope to its network, in Greenland, which will produce an even longer baseline (the maximum distance between telescopes) and give them an even larger virtual mirror. It’s only about 10%, but for interferometry techniques like this, it’s not just size that matters. The fidelity of the image—the accuracy and suppression of distortion—increases with the number of observing sites squared. Increasing from their previous six observing sites to seven means a 36% increase in image fidelity.

3. Put a radio telescope in spaaaace!

Need a bigger virtual mirror, but you’re all out of room on Earth? Just put a telescope in orbit. Not only would a space telescope give you a longer baseline for higher image resolution, but it could observe over its entire orbit, sweeping out a much bigger section of the virtual mirror and giving much higher image fidelity. And I don’t just mean low Earth orbit, either. Putting a telescope in a geostationary orbit would be four times better.

4. Look at other black holes.

Okay, this won’t exactly give us a better picture, but we might by chance find one that’s more photogenic. There are other black holes that the EHT can observe. The black hole in the center of our own galaxy, Sagittarius A*, is much smaller than M87, but it’s also much closer (by about the same amount, in fact), so it should look a little bigger. The EHT has already looked at Sgr A*, but unfortunately, being smaller means it also changes faster, making it harder to get a clear picture, because they take a long time to make. Still, expect to see this one in the next couple years.

Are there other black holes to look at? Well, M87 and Sgr A* are by far the best, but check out this paper, which lists nearby black holes by their apparent size in the sky. M87 is 42 microarcseconds wide, somewhat larger than expected, but Sgr A* is bigger still, at 53 microarcseconds. The next biggest black hole is the one in the Andromeda Galaxy at 19 microarcseconds. The Event Horizon telescope should just barely be able to manage that, but with that space-based telescope I mentioned, it’ll be easy, and there should be half a dozen more black holes that are observable. With a sample size of nine instead of one or two, we should be able to learn a lot more about black holes and the environments around them.

All of these developments are definitely or probably coming in the next few years, so I’m excited to see what new things we learn about the universe from them.

About Alex R. Howe

I'm a full-time astrophysicist and a part-time science fiction writer.
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