Real Photos of Black Holes
Actual Photo of Black Hole
Black Holes Are Real
Black holes are, simply, a place where so much matter has come together that its massive gravity draws everything near it towards it— even light. Once matter or light passes the "event horizon" of the black hole, it cannot escape (usually). However, we can see stars, gas and dust falling towards that point. Objects being drawn in by a black hole are heated up and emit bursts of visible light, x-rays, gamma rays and other wavelengths as they are torn apart.
Black holes were once theoretical, suggested by the mathematical equations of physics and Einstein's relativity, which predicted what would happen if too much mass collected in one spot. There was debate about whether black holes really existed; Einstein himself thought they were "too strange to be real."
"When I was a PhD student, people used to giggle when you hear[d] about black holes. They're like unicorns, mythical creatures. We call this the 'giggle factor.' People would say, 'Beam me up, Scotty.' Well, no one is laughing anymore."
~ Dr. Michio Kaku, Theoretical Physicist, on . How the Universe Works
The first known black hole was Cygnus X-1, discovered in 1964 as a powerful, mysterious source of x-rays. Since then, thousands of black holes have been discovered through the energy emissions of their dying prey or their tugs on nearby stars, dust, gas, and even galaxies. So we usually have to content ourselves with artist's depictions or a graph of the black hole's vital signs. However, our most powerful telescopes can sometimes detect the "accretion discs" of matter circling around black holes:
REALLY Supermassive Black Hole: Heart of NGC 1277
If Black Holes Are Black, Then What Are We Seeing?
This video gives us a simple demonstration of how a black hole works. Once something falls into the hole, the "event horizion," its light can't escape, but until then we can see it.
Notice how the coins speed up more and more as they get close to the "event horizon" (around 0:50). With a black hole, this acceleration can be thousands of miles per hour! At that speed, matter heats up, gets ripped apart, collides with other particles, and whips out all kinds of energy and particles at speeds approaching the speed of light. This energy can squirt out at a black hole's poles as massive jets, following the magnetic lines of force generated by the material speeding around the black hole.
Simulation of Black Hole
A Black Hole to Be?
Stellar Mass Black Holes
"Stellar Mass" black holes started out as giant stars at least twenty times the mass of our sun. (The black hole left behind may be as small as 2.5 times the sun's mass, and some are less than 20 miles wide).
All stars are engaged in a deadly tug-of-war between the force of gravity, which tries to make them contract under their own mass, and the outward thrust of their core's thermonuclear explosions. Once their fuel is used up, stars implode. Stars the size of our sun pack down into white dwarfs, small cold cores. Stars larger than our sun compact into neutron stars, super-dense remnants. The biggest stars explode their outer shells in a supernova, while their massive core collapses all the way into a black hole.
At the moment of collapse, massive stars emit extremely high energy bursts of gamma rays for a few seconds. Astronomers now know that these gamma ray bursts are the signal of the birth of a black hole. NASA's Swift telescope is designed specifically to pick up these bursts. It has also discovered some short gamma ray bursts caused by the collision and fusion of two neutron stars or by a black hole eating a neutron star.
In slightly over five years, Swift detected 500 gamma ray bursts, most of them the cries of newborn black holes. As of January 2012, that number is up to 738. The inescapable conclusion: black holes are not as rare as unicorns; they're actually fairly common, in a place as big as the whole universe.
Swift Spots a Black Hole Flare-Up
A Whopper Gamma Ray Burst
March 19, 2008 was a very special day in the life of NASA's Swift telescope. Not only did it detect four gamma ray bursts on the same day, a record, but also, one was the most luminous ever seen.
It was halfway across the universe, 7.5 billion light years away, and it was briefly so bright that it was visible to the naked eye. By comparison, the faintest naked-eye object we can normally see is galaxy M33, 2.9 billion light years away. (One light year is 5,878,625,373,183.61 miles).
A Black Hole in Andromeda Galaxy
How to See Mature Black Holes
We don't just see black holes being born; we can also glimpse older ones snacking on their neighbors.
The Hubble Space Telescope has actually spotted the flickering visible light of a blob of matter swirling "down the drain" of a black hole — oscillating as it spiraled towards and away from us, growing brighter and darker and brighter again in ever tightening repetitions — and then vanishing from sight.
More often, X-ray telescopes catch brief bursts of energy from the matter being shredded by the black hole (right).
Remember Einstein's equation, E=MC2? The energy is the amount released. The M is the mass of the star or other object disintegrating in the black hole's demolition derby. C is the speed of light, which is 670,616,629 mph. Remember how much energy the Hiroshima bomb released, converting just a minute amount of matter into energy? A sun's mass compared to a bomb-sized chunk of plutonium is... well... inconceivable. No wonder the resulting explosions flare so brightly.
A Black Hole Chomps on Its Companion Star
Close-Up of Black Hole
Most star systems in the universe are binary, so many black holes have a sibling to snack on. As this material is accelerated and ripped apart, it gives off a steady stream of x-rays. Sometimes an especially tasty chunk causes the whole accretion disc swirling around the black hole to brighten not only on x-ray wavelengths but even extending into visible light.
In April 2012, NASA's Chandra x-ray telescope detected a black hole in the galaxy M83 that was chewing off a big chunk of material from its companion star. Hubble and the European Southern Observatory's "Very Large Telescope" spotted the resulting glow in visible wavelengths.
Photo of a Supermassive Black Hole
Stars Orbiting Center of Milky Way
Supermassive Black Holes
Astronomers have been shocked to discover that most galaxies have a supermassive black hole at their center, far more massive than stellar mass black holes. Astronomers are still wrestling over competing theories about how these monsters formed. We do know that there is one in the center of the Milky Way!
There's so much dust and matter packed near the center of our galaxy that it's mostly obscured in visible light, although we know where it is: it's in the direction of the constellation Sagittarius. However, telescopes that use alternate wavelengths of energy like x-rays and infrared can peer through the murk and image what's at the center.
What they've found is surprising, and awe-inspiring. By taking images of the center of the Milky Way galaxy for over a decade, several teams of astronomers have pinpointed its central black hole, named Sgr A*. The Keck Observatory's timelapse photos (see more info) show stars whipping around...something... that is invisible, yet its supermassive gravitational pull is accelerating them to thousands of miles an hour.
Now and then telescopes glimpse the "burp" as something is drawn in, torn to shreds, and emits a dying burst of energy. (As Bad Astronomy's Dr. Phil Plait notes, it's not technically a burp, but "more like your food screaming loudly and incoherently and flailing around while you’re actually eating it.")
X-Ray Flare of Milky Way's Black Hole
Documentary on Milky Way's Black Hole
This excellent 2007 NOVA documentary (on DVD) explains how astronomers discovered the black hole at the center of the Milky Way. Good visuals, easy to understand.
Scary! Luckily, as we can see from the stars orbiting the Milky Way's hidden monster, you only get devoured if you get too close. Farther away, the pull of gravity is less, so stars can orbit the black hole just like our solar system's planets orbiting the Sun. Thankfully, our Sun is far away from the danger zone, orbiting the black hole safely from 26,000 light years away.
The European Southern Observatory has produced a slick video showing off its own timelapse photos of the center of the Milky Way:
ESO's Video of Stars Orbiting Black Hole in Center of Milky Way
Visible-Light Jet from Black Hole in M87
Supermassive Black Holes: Cosmic Blow Torches
The matter and gas falling towards black holes spins nearly the speed of light. With some supermassive black holes, small particles of that chewed-up matter squirt outward, streaming away from the poles of black holes as enormous jets, like potato peelings flying out of a food disposal when it's fed too quickly.
Astronomers and physicists are still struggling to explain the exact cause and physics of these jets, but telescopes have imaged many of them. The jets are visible at many wavelengths, including visible light (right)
Another Beautiful Photo of Supermassive Black Hole Jets
A Quasar in Double Vision
The Mystery of Quasars Solved
Studying supermassive black holes has helped astronomers untangle a decades-old mystery.
In the early 1960s, scientists puzzled over quasars, "quasi-stellar objects," that appeared to be as bright as nearby stars but were incredibly distant. They produced especially strong signals at radio wavelengths, yet another part of the electromagnetic spectrum along with light, gamma rays and x-rays.
Most astronomers now agree that quasars are actually the highly energetic, glowing discs of matter orbiting supermassive black holes at the cores of distant galaxies. From our vantage point, they shine brighter than all the stars in the rest of the galaxy.
There are some hints that these quasars are glimpses of what galaxies looked like when they were very young. We only see quasars extremely far away from the Milky Way. Remember, even light can only travel so far each year, so looking far out into the universe means looking back in time.
Great Black Hole Video
Fantastic "Black Holes" episode on "How the Universe Works," my favorite astronomy program on streaming Amazon Instant Videos (free for Amazon Prime members, also on Netflix).
- HubbleSite - Black Holes FAQ
The Hubble Space Telescope's website explains what black holes are, what we know about them, and how we can detect them.
- McDonald Observatory's Black Hole Encyclopedia
Great site all about black holes. It includes a directory of known black holes, from stellar mass sized black holes to supermassive black holes.
- Black Hole Accretion | Berkeley Science Magazine
This 2005 scholarly article on black holes is pretty technical, but it's an excellent summary — if you can decipher it — of the science of black holes and their accretion discs, their physical structure, and how we can detect them.