JUNE 8, 2015
Welcome, earthlings, to the place of no return — a region in space where the gravitational pull is so strong, not even light can escape it. This is a black hole.
It’s ok to feel lost here. Even [Albert] Einstein — whose Theory of General Relativity made it possible to conceive of such a place — thought the concept was too bizarre to exist. But Einstein was wrong, and here you are.
You shouldn’t be here. You will surely get pulled in. But fear not dear Earthling, this is just your mind thinking. It has taken your brain millions of years to get here. So let’s get started.
Bright flares are visible near the event horizon of a super-massive black hole at the center of the Milky Way. Credit NASA/CXC, via MIT, via F.K.Baganoff
The black hole is a hungry beast.
It swallows up everything too close, too slow or too small to fight its gravitational force — even light. With every planet, gas, star or bit of mass consumed, the black hole grows.
At the edge of a black hole, its event horizon, is the point of no return. Stay far away from the event horizon, because that’s where the hole pulls in light. And nothing is faster than light. At the event horizon, everything enters the black hole.
The brightest white spot in the middle is the very center of the Milky Way galaxy, which also marks the site of a supermassive black hole. Credit NASA/JPL-Caltech
Pretty much everything we understand about how the universe works, depends on the black hole.
Someone is wrong, or we have to admit that earthlings still aren’t equipped to understand the universe. The firewall paradox calls to question the most definitive theories of science. Albert Einstein, Joseph Polchinski or Stephen Hawking, or none, everything we know about the universe could change if we could know for certain what happens to information inside a black hole.
An interpretation of a black hole, created for an educational video game. Credit Denver Museum of Nature and Science
If you fell into a black hole, it’s not clear how you would die.
Will gravity rip you apart and crush you into the black hole’s core? Or will a firewall of energy sizzle you into oblivion? Could some essence of you ever emerge from a black hole? First posited by a group of theorists including Donald Marolf, Ahmed Almheiri, James Sully and Joseph Polchinski in March 2012, the question of how you would die inside a black hole is probably the biggest debate in physics right now. It’s called the firewall paradox.
Based on the mathematics in Einstein’s 1915 General Theory of Relativity, you would fall through the event horizon unscathed before gravity’s force pulled you into a noodle and ultimately crammed you into singularity, the black hole’s infinitely dense core.
But Dr. Polchinski and his team pitted Einstein against quantum theory, which posited that the event horizon would become a blazing firewall of energy that would torch your body to smithereens.
Keep both theories, the physicist Stephen Hawking said in January 2014. Black holes aren’t what we thought they were. There is no event horizon, and there is no singularity. They’re just different.
According to Dr. Hawking, at the edge of a black hole, the fourth dimension known as space-time fluctuates like weather, making the crisp edge we assume impossible. Instead, Dr. Hawking’s “apparent horizon” would be like a purgatory for light rays attempting to escape a black hole, slowly dissolving and moving inward, but never being pulled into singularity. The event horizon, he says, remains the same, or even shrinks as a black hole slowly leaks energy. Suspended in the apparent zone, you would scramble and leak out into the cosmos as “Hawking radiation.”
Galaxy NGC 1275. Credit NASA
Black holes can sing.
In 2003, an international team led by the X-ray astronomer Andrew Fabian discovered the longest, oldest, lowest note in the universe — a black hole’s song — using NASA’s Chandra X-ray Observatory.
Although it is too low and deep for humans to hear, the B flat note, 57 octaves below middle C, appeared as sound waves that moved out from explosive events at the edge of a supermassive black hole in the galaxy NGC 1275.
NGC 1275 per NASA/ESA Hubble
The notes stayed in the galaxy and never reached us, but we couldn’t have heard them anyway. The lowest note the human ear can detect has an oscillation period of one-twentieth of a second. This B flat’s period was 10 million years.
The “songs” of black holes may be behind a declining birth rate of stars in the universe. In clusters of galaxies such as Perseus, the home of NGC 1275, the energy these notes carry is thought to keep the gases too hot to condense and form stars.
A big galaxy gobbles a tiny one. Credit Swinburne University of Technology/Reuters
Meet the management: Black holes may control the size of a galaxy.
Playing music that keeps the intergalactic clusters too hot for stars might not be the only way black holes help maintain galaxies.
Astronomers think that the energy that forms when galactic masses swirl and heat up around a black hole shoots out in X-ray beams that fuel quasars, supermassive black holes that are actively chomping down gas at the centers of distant galaxies.
The Milky Way as visible from the desert southwest of Cairo. Credit Amr Abdallah Dalsh/Reuters
Astronomers have evidence for black holes in nearly every galaxy in the universe.
Although no black hole is close enough to Earth to pull the planet into its depths, there are so many black holes in the universe that counting them is impossible. Nearly every galaxy — our own Milky Way as well as the 100 billion or so other galaxies visible from Earth — shows signs of a black hole.
Of the billions of stars in the Milky Way, about one in every thousand new stars is massive enough to become a black hole. Our sun isn’t. But a star 25 times heavier is. Stellar-mass black holes result from the death of these stars, and can exist anywhere in the galaxy.
Supermassive black holes — a million to a billion times more massive than our sun — exist only in the center of a galaxy. At the center of the Milky Way, 26,000 light-years from Earth, scientists are hoping to make an image of Sagittarius A*, which is believed to be our own supermassive black hole, with the mass of four million suns. How supermassive black holes form is still a mystery.
Sagittarius A* from NASA’s Chandra X-Ray Observatory
Black holes are stellar tombstones.
It wasn’t a nuclear bomb, and it wasn’t terrestrial. On July 2, 1967, a network of satellites recorded an explosion of gamma rays coming from outer space. In retrospect, this was one of the first indications that black holes are real. Today, scientists believe that the gamma ray burst is the final breath of a dying star and the birth of a stellar-mass black hole.
The dramatic transformation starts when a massive star runs out of fuel to power itself. As the star begins to collapse, it explodes. The star’s outer layers spew out into space, but the inside implodes, becoming denser and denser, until there is too much matter in too little space. The core succumbs to its own gravitational pull and collapses into itself, in extreme cases forming a black hole.
Theoretically, if you shrunk any mass down into a certain amount of space, it could become a black hole. Our earth would be one if you tried to cram the earth into a pea.
NASA’s Hubble Space Telescope captured a high energy blast, likely a black hole eating, at the center of a galaxy. Credit NASA
‘A black hole has no hair.’
On March 28, 2011, astronomers detected a long gamma ray burst coming from the center of a galaxy four billion light-years away. This was the first time humans observed what might have been a dormant black hole eating a star.
No matter what a black hole eats — a star, a donkey, an iPhone, your grammar teacher — it’s all the same. As the physicist John Archibald Wheeler put it, “A black hole has no hair,” meaning that a black hole remembers only the mass, spin and charge of its dinner.
The more a black hole eats, the more it grows. In 2011, scientists discovered one of the biggest black holes ever, more than 300 million light-years away. It weighs enough to have gobbled up 21 billion suns. Scientists want to know if the biggest black holes are the result of two holes merging or one hole eating a lot. But scientists don’t know how they grew so large.
The Event Horizon Telescope is attempting to get the first ever portrait of the hungry monster at the center of our galaxy. Credit James D. Lowenthal/Smith College Astronomy Department
To find the darkness, follow the light.
Because light can’t escape a black hole, seeing what’s inside it is impossible. Getting a picture of a black hole’s edge is difficult, and getting a clear picture is an event.
Actually, it has never been done. Scientists suspect black holes when their tools detect high-energy radio waves, such as those that may result from a collapsing star, gamma ray burst, supernova or the energy an object might release before reaching the black hole’s event horizon. Generally, if there is a lot of energy with a massive core at the center of a galaxy, the core is probably a black hole.
The Event Horizon Telescope, the one Sheperd Doeleman and his colleagues used to try to photograph Sagittarius A* and M87, another black hole, featured a cast of more than 100 scientists on three continents and one very important crystal used to calibrate atomic clocks. The scientists staked out seven telescopes atop six mountains, synchronized time, pointed their discs at the sky and waited. For the first time ever, scientists may have seen a rough image of a black hole’s event horizon.
An artist’s conception of stars moving in the central regions of a giant elliptical galaxy that harbors a black hole. Credit Lynette Cook/Gemini Observatory, via Nature, via Associated Press
A black hole is not forever.
As Hawking radiation leaks out into the universe, quantum effects suggest that a black hole will evaporate — eventually. It would take many times the age of the universe for a black hole to fully evaporate.
Dr. Hawking, like Einstein, at first did not believe his own theory. But the numbers were right. Physicists now view his result as the backbone for whatever future theory will bring together gravity and quantum theory.
This magnet is part of The Large Hadron Collider, the world’s largest and most powerful particle accelerator. [at the European Organization for Nuclear Research (CERN) in Geneva, Switzerland. ] Credit Fabrice Coffrini/Agence France-Presse — Getty Images
A giant magnet in Europe will not destroy the planet.
Before the European Organization for Nuclear Research fired up the Large Hadron Collider in 2008, critics worried that smashing together protons in a 17-mile ring underground would create a black hole that would swallow the earth.
LHC at CERN
Worriers echoed apocalyptic cries about Brookhaven National Laboratory’s Relativistic Heavy Ion Collider that the center’s scientists had squelched nearly 10 years earlier.
RHIC at BNL
According to their calculations, ultrahigh-energy cosmic rays already penetrated the earth’s atmosphere and predicted about 100 tiny black holes on earth every year. If tiny black holes were a problem, Earth would have already collapsed into infinity:
Still, in June 2008, a safety review proclaimed the L.H.C. was indeed safe. Experiments commenced, the Higgs boson was found, and the earth survived after all.
In the search for the smallest particles in the universe, the consequential mini black holes that scientists might create in contained underground tubes would let them observe general relativity and quantum mechanics in action and may open the door to solving the firewall paradox.
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