Black Hole: Extreme Exploration
Imagine a thing made of nothing but space and time. Imagine a place that is a one-way exit from our universe. Imagine an object that can stop time and tear a star apart, atom-by-atom.

This is not science fiction, but a description of the strangest of Nature's creations, a black hole. The modern notion of a black hole came from the mind of Albert Einstein when, almost a century ago, he created a new way to think about gravity that lead to some wild possibilities, including black holes. Nobody at the time, including Einstein, believed they could possibly exist in reality. Now, with the help of advanced space telescopes such as NASA's Chandra X-Ray observatory, we have come to realize not only that black holes are real, but also that they are everywhere! Let's explore the darkest and most extreme place in the cosmos, the realm of the black hole.

An image with a black background and bright blue material falling into a black hole.  The center/left of the image is a small black circle, surrounded by a disk of blue material, and jets of blue/white material flowing vertically away up and down.  Off to the right is a hot white star with a white band of material being pulled off and onto the black hole disk.
How do we know black holes exist? We can't see them (they are, after all, black holes!), but we can see the effect they have on other, more familiar objects close to them.

Image to right: As we round the giant hot blue star, we see its tiny companion, a black hole whose gravity is so intense that it is stripping the outer layers of gas from the star. Credit: (NASA/Honeywell Max-Q Digital Group/Dana Berry)
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Look at the animation above as we take an imaginary journey to a black hole. Our destination is Cygnus X-1, an otherwise normal, hot blue star that lies in the constellation Cygnus the Swan. Turning an X-ray telescope on to Cygnus X-1 we are flooded by powerful X-ray light, more intense than even the hottest star is capable of producing.

As we move around the star, we see that it's not alone. There is a small companion, seemingly linked to the star by a streamer of hot gas. The companion is drawing off the outer layers of the star, and spinning its gas into a pancake flat disc. The gas is orbiting at millions of miles an hour, and bubbles and boils at million degree temperatures. When gas is this hot, it blazes in X-ray light. At the center of the disc, no greater in size than a city, we see that the companion is a black hole.

An image of a black hole with surrounding energetic disk of material in multicolored bands of blue, yellow and red, on a black background.
Image to left: The spiraling disc of gas gets hotter and hotter as it nears the black hole. On the point of falling into the black hole, the gas glows X-ray hot. Credit: NASA/GSFC
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But where did this black hole come from in the first place? A few million years ago, Cygnus X-1 was a pair of ordinary, but very large stars. The more massive of the pair used up its supply of nuclear fuel rapidly, and once its core was exhausted of energy, its violent death was swift and devastating. While the outer atmosphere of the star was blown into space in a gigantic explosion called a supernova, its dense core shrank under the irresistible squeeze of gravity, disappearing inside a black hole.

A black hole is the fate of only the very largest of stars. It will not be the fate of our Sun, which simply lacks the mass needed to create a black hole. And because hot gas torn from a companion star is the fingerprint astronomers use to locate black holes, we can only spot black holes that have a companion star. However, astronomers think that there may be up to a million black holes in our Milky Way galaxy, and that this is a typical number for other galaxies as well. It is the task of X-ray telescopes such as Chandra and XMM-Newton to go exploring for the tell-tale glow of X-rays that reveal the locations of darkest places in the universe.

A black background with bright yellow points.  Surrounding these is a fuzzy veil of purple gas and dust.
Image to right: A view towards the center of our neighbor the Andromeda galaxy, as seen by the Chandra X-ray telescope. The yellow fuzzy dots are the glow of X-rays, each revealing the location of a possible black hole and its companion star. Credit: NASA/CXC/SAO

Related Resources

Chandra X-ray Telescope
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Chandra Education
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XMM-Newton X-ray Telescope
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XMM-Newton Education
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For kids 14 and up, check out some neat black hole stuff:
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Published by the Office of Space Science