When radio waves from the depths of a nearby galaxy known as Messier 87 traveled some 55 million light-years to a constellation of telescopes on Earth, revealing to humanity the face of a black hole for the first time, people around the planet paused in wonder.
Why does it look like a doughnut? How scary is it when two of these things smash into each other? And if light can’t escape a black hole, what are we even looking at?
Our coverage Wednesday of the first ever image of a black hole, by our cosmic reporter Dennis Overbye, drew a huge response from our readers. Dennis graduated from M.I.T. with a physics degree and was a Pulitzer Prize finalist in 2014 for his coverage for The Times of the race to find the Higgs boson. He sat down Thursday with his feet on his desk, beside a photo of the black hole, to answer some of our readers’ questions and respond to their feedback.
What does this image really tell us besides black holes are round?
This is the first look into the central engine that generates the enormous energies put out by quasars, radio galaxies and other so-called active galactic nuclei. The action all starts down at the edge of oblivion, in a maelstrom of hot gas, gravity, magnetic fields and otherworldly pressures. It extends out beyond the far reaches of the galaxy, as jets of radio-wave energy moving at nearly the speed of light; these lobes of radio energy can accompany shock waves capable of blowing the gas out of galaxies or even entire clusters of them, preventing stars from forming. Through these mechanisms, black holes, blowing hot and cold, control the growth and structure of galaxies. It all starts in the accretion disk, the doughnut of doom.
Why does it look like a “doughnut of doom” and not a sphere?
When matter falls together into a black hole, or in almost any other situation, it has angular momentum, and takes on the shape of a flattened pancake spinning around the central attraction. Also, the black hole is probably spinning, pulling the disk around in the same direction. We are seeing the disk almost directly face-on, so it looks like a doughnut hole. (From edge-on it would look different.) Bent by gravity, light wraps around the hole on its way to our eyes, so the black hole magnifies and distorts the image of the accretion disk.
Will we ever get a clearer image of this black hole?
We will. The key is to observe black holes at shorter and shorter radio wavelengths, which allows more and more detail to be resolved. The latest images were recorded at a wavelength of 1.3 millimeters in the microwave band. The Event Horizon team hopes to go to shorter wavelengths in the future, and to use more antennas, including one in space, which would increase the size of their "virtual telescope" and also increase resolution.
Do you feel that coverage of the breakthrough minimized the role of Katherine Bouman, a researcher at the Harvard-Smithsonian Center for Astrophysics?
The issue of the unsung hero or heroine is a big problem, especially in Big Science, which the Event Horizon Telescope is surely part of.
There were 207 people in the collaboration, according to one of the physicists I talked to that day. I am sure that many crucial contributions and rich anecdotes of behind-the-scenes science got missed.
In time, these will come out in more thoughtful, longer narratives. On the day of the announcement there was a tsunami of information released at 9 a.m., and a rush to post stories as soon as possible, an unfortunate fact of the internet age.
[The Times published an article about Dr. Bouman after Dennis signed off Reddit.]
What does current science tell us is supposed to happen in the gravitational extremes of a black hole?
That’s the biggie everybody wants to know. Whatever happens there, it probably is similar to what happened, maybe in reverse, in the Big Bang. Space, time, matter all go away, replaced by what? Some people think the answers might come from string theory, which unites gravity with quantum theory. But for now it remains an untestable, but mathematically elegant, speculation.
What happens when two black holes collide?
Such collisions have happened and been recorded by the LIGO gravitational wave observatory. They vibrated the space-time continuum like a drum and released as much energy in a fraction of a second as all the stars in the observable universe. The result in each case was an even bigger, blended black hole.
But outside the event horizon, the gravitational field of a black hole is just like that of a star and it is no more dangerous. Black holes don't go roaming around looking to swallow you. They only hurt if you touch them, in which case you won't ever be able to let go. Otherwise they are like any other animal that you would just let go, and mind your own business.
How is any of this relevant to our day-to-day lives?
It can certainly provide context to your daily life, but it won’t move the markets. It will, or could, move your soul. However, Einstein, when he invented the sort of trampoline universe described by general relativity, did not dream that it would lead to pocket devices that keep time and tell you precisely where you are on Earth — that is to say, GPS. But they depend crucially on general relativity to tell you where you are. So who knows?
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