How do black holes emit light?

Black Hole Accretion Disc Light Massive Color Picture Artist's Rendition Weekly Show

If there’s one thing everyone knows about black holes, it’s that they give off no light. These behemoths of time and space erase objects from history, swallowing everything in their paths. Yet a few minutes of research will tell you we can detect black holes through their radiation. In fact, black holes are supposedly some of the brightest objects in the universe. Welcome to the bizarre world of astrophysics.

First of all, your science teachers were telling the truth: black holes give off no light. As their namesake implies, these objects have grown so massive not even light can escape their gravity. If a rogue black hole flew between us and the stars, the only way to detect it would be through its gravity. Astrophysicists have shown, however, that most matter in the universe clumps together. Stars live in galaxies, and galaxies move in clusters. Black holes often live at the centers of galaxies or alongside stars throughout them.

Black Hole Accretion Disc Light Massive Color Picture Artist's Rendition Weekly Show

An artist’s rendition of an accretion disc. Scientists have yet to understand why the black hole emits particle streams on polar axes.

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Why classical physics says the sun doesn’t shine

In the first half of the twentieth century, physicists discovered something alarming about the sky. When they looked up, they saw the sun—and it was shining. You see, according to their calculations this was impossible. Their models stated that the sun was not enough energy to shine. Despite their efforts to explain the problem, the numbers were loud, clear, and anything but bright.

First, some background on the sun. Like all stars, the sun converts its mass into energy via nuclear fusion. In short, the gravity of its outer shells heats the core until it can convert hydrogen into helium, producing enough energy to support itself. This process gives off immense radiation, which we perceive as heat and light. I explained how stars work a few weeks ago—click here to learn more.

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How to look back in time (actually)

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Time travel. The idea has captivated humans for millennia. Ancient myths and science fiction imagine rips in the universe, portals that let us observe history before our eyes. What most people do not realize, though, is that they do this every day.

Back Future Doc Delorean Time Travel Stars Past Weekly Show

“We’re gonna need a bigger car.”

Let’s step back—four hundred years back. In the mid-seventeenth century, astronomer Ole Romer noticed something strange about Jupiter’s moons. When they came close to Earth, the time between their eclipses was short, but when they moved farther away the time in between them was longer. Many scientists at the time believed light traveled instantaneously, that our eyes observed Jupiter and its moons in real time. This meant that the moons’ orbits changed depending on their position relative to Earth. It also made no sense.

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