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What is a black hole? Do black holes even exist? How are black holes formed? Can we see black holes?

Supermassive black HolesEven the most commonly asked questions on black holes are difficult to answer. Black holes are the ultimate unknown — these rents in the fabric of spacetime let nothing, not even light, escape. Yet we know they exist in part because of the light shed by their surroundings. Ironically, the blackest objects of the universe can also be surrounded by some of the brightest stuff. Supermassive black holes at the centers of galaxies become powerful beacons when they feed — gas that flows into these gaping maws heats up and glows so bright that it can be see all the way from the early universe.

Each of the four articles in this free ebook from Sky & Telescope magazine helps reveal the mysteries of supermassive black holes, including how they form and what role they play in the larger galaxy. And one day, we might even be able to observe the beasts themselves.

This free eBook from Sky & Telescope magazine includes four articles from the experts, who explain various theories and facts about black holes.

  • "A Quasar in Every Galaxy?" by Robert Irion summarizes observations and theories about the supermassive black holes that exist in the core of almost every major galaxy.
  • "How Black Holes Helped Build the Universe" by Christopher Wanjek shows how, without black holes, we wouldn't recognize the universe around us, and we might not even exist.
  • "Spinning Hearts of Darkness" by Laura Brenneman observes spinning black holes to help answer a fundamental question: how are black holes formed?
  • "Einstein's Shadow" by Camille Carlisle introduces a planet-wide telescope — the global Event Horizon Telescope — that has set its sights on imaging a black hole's silhouette. One day soon, we will have direct evidence that black holes are real.

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Peek Into Sky & Telescope's Black Holes eBook: Learn Black Hole Facts & Theories!

Black holes are things of wonder. These dark beasts become bright beacons of light when they feed on hot gas, yet they remain shrouded in mystery. Many questions remain unanswered: How do black holes form? What role do they play in galaxy formation?

What we do know is that without black holes, the world as we know it might be entirely different. Black holes shape the universe's evolution; without them, we might never have come into being. To learn more about these beasts, astronomers peer into the heart of nearby galaxies and measure black hole spins, which hint at how black holes formed and grew. And plans are underway to directly observe a black hole!

A Quasar in Every Galaxy? By Rob Irion

Article #1: A Quasar In Every Galaxy?

by Robert Irion
Observations are showing that in the heart of every major galaxy, there exists a supermassive black hole millions or even billions of times the mass of the Sun. And not every one of these black holes shines bright as a quasar. When they starve, the black holes can't be seen. It's only when they feed on gas that they flare up for brief, glorious intervals. Even our very own supermassive black hole in the Milky Way could exhibit a magnificent display when it collides (several billions of years from now) with our neighbor, Andromeda Galaxy.

How Black Holes Helped Create the Universe by Christopher Wanjek

Article #2: How Black Holes Helped Build the Universe

by Christopher Wanjek
Without the black holes we find all across the universe, our galaxy and even our world might look entirely different. By feeding on gas, black holes have been serving as the chief architects of the universe. The energy they consume, and that they blow away, triggers star formation, makes or breaks galaxy formation, and redistributes elements in a way that might have enabled life itself.

Spinning Hearts of Darkness by Laura Brenneman

Article #3: Spinning Hearts of Darkness

by Laura Brenneman
However massive they are, black holes don't usually just sit there — they spin, sometimes at tremendous rates. Astronomers are measuring the rotation rates of black holes to find out how they formed, and how they grew over time.

Einstein's Shadow by Camille Carlisle

Article #4: Einstein's Shadow

by Camille Carlisle
The best way to learn about black holes, of course, would be to image one directly, a challenging task. But a group of astronomers is putting together a planet-wide telescope that aims to do just that — take black hole pictures.

Learn about black hole theory and more when you download your
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