‘The Donut of Doom’


By Tom Burns - Stargazing



Recently, one of the students in my Popular Science Writing class complained to me about the flood of Internet memes ridiculing the recent ground-breaking image of the M87 black hole. For example, one Internet wit called it the “Donut of Doom.”

Harrumph. I’ll have you know that a team of 200 scientists from all over the world created the image of that tantalizing torus. They used a network of eight radio telescopes, collectively called the Event Horizon Telescope, on four continents. Off and on for 10 days, those telescopes gathered the data behind the image. For two years, computer programmers meticulously analyzed and compiled that data.

M87, the galaxy that the black hole is centered in, is a rather distant 55 million light years away. It contains trillions of stars, not the mere hundreds of billions in our own Milky Way galaxy. The black hole alone contains material equivalent to billions of stars like our sun.

The Internet seems petty indeed when it trivializes such a mammoth accomplishment centered on such an enormously important object.

However, I can’t say that I agree with my student. The jokes about the black hole show that people have made a personal connection to the image, even if their emotional outpouring is in the form of mostly bad humor.

My favorite is a cartoon in the New Yorker. Out of the black void at the center of the oval accretion disk arises a thought bubble. The black hole is thinking, “I have absorbed all matter within my gravitational pull. I should be happy …”

So I said to my student, “Count your blessings. People are paying attention. It becomes our job to correct any misunderstanding and show people the hidden significance of the image.” So let’s go!

Astronerds like me have good reason to be excited about the image. However, like my student, I cannot help but suppress an eye roll or two. The image is decidedly not a picture of a black hole. Such an image is, by definition and by the laws of nature, impossible.

What you see when you look at the smallish orange and yellow ring is far more important than an image of a black hole. It constitutes further proof that black holes exist in the first place.

That’s right. Black holes are predicted by the work of Albert Einstein and other very smart physicists and astronomers. They have assumed their existence when doing their complex mathematical calculations about the universe. However, the actual existence of black holes has always been an open question.

Seeing is believing, of course. Since astronomers cannot take an image of a black hole, they must look instead for the effects that a black hole should have on the universe around it. The Donut of Doom conclusively fills that bill.

However, getting to that conclusion requires a bit of explanation.

Astronomers can model the life and death of a very large star and thus, predict what happens when it dies.

Small stars like the sun collapse to a dense ball of matter called a white dwarf. Such dead stars are a few thousand miles wide, about the size of a small planet like Mars.

Much more massive stars start out with a lot more stuff. The powerful gravitational effect of such a mass causes it to collapse to an even smaller size. Depending on the total mass, its volume might reduce to the size of a basketball or an orange, or even (here it gets really weird) virtually nothing at all.

When they die, truly gigantic stars, astronomers think, reduce themselves to a volume of zero size, a spot in spacetime astronomers call a singularity. The volume of all that star stuff has essentially disappeared from the universe, yet its collective gravity, an inconceivably concentrated gravitational force, remains. The mind boggles at a place in space that has been described as “pure gravity,” enormous mass distilled into its gravitational essence.

The black hole’s gravitational field is so great that even light cannot escape. No light means no photographic image. Try taking a picture in a completely dark room and you’ll see what I mean.

The black hole has essentially sealed itself off from the rest of the universe. The precious laws of nature that determine the functioning of the universe and the conduct of our daily lives no longer function.

We are thus left with two distinct black-hole realms: the gravity-bound region close to the black hole where even light cannot escape and the region just outside where material is streaming into the black hole.

Those two realms are divided by an almost magical boundary called the event horizon. It resembles our earthly horizon in at least one respect. You can see the things near it, but you can’t see past it.

As a result, to detect and understand black holes, astronomers must look just outside the event horizon where the black hole’s gravity cannot suck light in.

As the material spirals in toward the event horizon, it flattens out into a swirling donut-shape called an accretion disk. It is that accretion disk, seen from the top, that you see in the Donut of Doom image.

That donut area ought to be an extremely active place. As material steams toward the black hole, the enormous gravity of the black hole tears atoms and molecules into their subatomic components.

Those subatomic particles slam into each other with velocities approaching the speed of light. Both the tearing apart and the slamming together produce prodigious numbers of high-energy particles, many of which will be in the form of light particles collectively known as photons.

Our own galaxy, the Milky Way, contains a plenitude of black holes that are relatively close by, but astronomers chose to image the one in M87, a wholly different galaxy much farther away.

Why then didn’t the astronomers simply choose a black hole created from the collapse of a nearby star in our own Milky Way galaxy?

As it turns out, a second type of black holes exists in our universe. They reside at the centers of galaxies, and they make a stellar black hole look like a speck of dust by comparison.

In fact, most galaxies, including our own Milky Way, appear to have black holes at their center. They formed out of galactic gas and dust that suffered a cataclysmic gravitational collapse early in the galaxy’s formation. That material never got a chance to form into stars.

Our own Milky Way has such a black hole at its center. So why didn’t the M87 team image that one?

In fact, they did. While they were engaged in the M87 project, they also took data from the Milky Way’s central black hole. But at only (yes, only) two million solar masses, our black hole was not very photogenic.

On the other hand, the black hole at the center of M87 is the mother of all such objects.

The gravitationally bound area inside the event horizon of the M87 black hole is stunningly small at a mere five times the diameter of our solar system out to Pluto. At its center is crammed a collection of material with a mass of 6.5 billion suns.

The image of M87’s black-hole accretion disk is resolved down to the “last photon orbit,” as astrophysicists love to put it. In the middle is a darkness as black as the total absence of light can make it.

By looking at that “last photon orbit” near the inner edge of the ring, astronomers can get a glimpse at the event horizon, the place of “zero width” where the laws of the universe cease to function. They may thus examine the locus of mind-bending transition where our universe, governed by natural law, ends and the mysterious realm of the black-hole universe begins.

If you could manage to plunk yourself down at the last photon orbit, “you could see light reflected off the back of your head after completing a round trip. Or, if you turned around quickly enough, you might see your own face. Closer than that, all the light falls in,” writes Janna Levin, professor of physics and astronomy at Barnard College in her book Black Hole Blues.

The image has important public relations and symbolic value, to be sure.

When you compare its apparent simplicity with the time and expense it took to produce it, it seems silly. Thus, I don’t mind the Internet memes at all.

Perhaps people will understand the importance of the Donut of Doom if they consider the amount of data it took to produce it. We’re talking five petabytes here. That’s five million billion bytes of information, a five with 15 zeroes after it of individual data points.

In effect, a mountain of data has been condensed to a single public-relations image of a mountain.

So make fun of the image if you will. However, as pathetic the picture might look, the mountain still stands, grand and glorious, waiting for hundreds of scientists to meticulously climb to its summit.

Decades will pass before they reach the top. Over the course of time, they will make the invisible and incomprehensible black hole visible and comprehensible. They will help us to understand a place in space and time where the laws that govern our more familiar universe do not apply.

The long, hard climb is fraught with immense complexities. It even has its dangers. From their high perch at the summit, they may well see that our old understanding of the universe and its laws is deeply flawed or perhaps even fundamentally incorrect. But the climb is still well worth the effort. After all, isn’t that what science is all about?

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.