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What
if a black hole formed near our solar system?
Black holes rank among the most fearsome phenomena in the universe. Their gargantuan gravity warps space and time and our understanding of them almost to the breaking point. Looming larger still are the supermassive black holes skulking in galactic cores, the repositories of millions to billions of stars’ worth of matter.
What mayhem might one of these black beasts bring if it formed, or passed, near our solar system?
As with most hypothetical questions, the devil is in the details. How close would the black hole approach as it swung by? Where would it come from? How massive would it be?
First off, our sun will never become a black hole; it would need 10-15 times as much mass in order to undergo the kind of gravitational collapse required [source:GSFC].
Nor will any stars in our galactic neighborhood undergo the big crunch: Most nearby twinklers are red dwarfs mighty mites as common as Starbucks in Seattle and pack only a fraction (8-60 percent) of our sun’s mass [sources: Encyclopaedia Britannica, Filippenko].
That leaves two possibilities: Either a black hole spontaneously forms in our vicinity, or a rogue passes nearby. The protestations of Large Hadron Collider naysayers notwithstanding, we can discard the first possibility (we’ll explain why later).
As for the second possibility, astronomers and astrophysicists confirmed the existence of wandering black holes in 2000, but the chances of one hitting us are roughly nil [sources: 20/20; Unruh].
As novelist Douglas Adams once put it, "Space is big. You just wont believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think its a long way down the road to the chemists, but thats just peanuts to space."
That said, the possibility is far too interesting not to explore.
What is Black Holes ?
Black Hole Effects on Space and Time
From a distance, a black hole acts like any massive, gravitational object: Until its right on top of you, it follows classical mechanics and Newtons law of universal gravitation, which tells us the attraction between two objects is proportional to their masses and drops off rapidly with distance. In other words, theres no gravitational difference between R136a1, a blue dwarf star weighing 265 suns, and a 265-solar-mass black hole [source: Fazekas].
Approach close enough for a black hole to wrap you in its gravitational sleeper hold, however, and youre grappling with a different set of rules: Einsteins general theory of relativity, which predicted black holes, says that gravity also warps space and time, and that extreme gravity does it, like Vanilla Ice, to the extreme.
If you wanted to study a black hole from a starship, youd find that, the closer you got to the monstrous mass, the more oomph your engines would have to kick out to maintain a circular orbit. At first, firing off the occasional rocket burst would suffice to stabilize you; closer in, and youd have to expend enormous energy just to maintain an irregular orbit. Closer still, and nonstop rocket burn would be all that stood between you and annihilation.
Once you ran out of fuel (or succumbed to space madness and turned off the engines), you would spiral in to the black holes event horizon, a boundary beyond which nothing, not even light, can escape. From there, youd have a date with destiny: Nothing you could do would stop your inexorable journey toward the singularity, a core of infinitely distorted space-time where physics as we know it curls up in a ball and whimpers.
All through your approach, time would have slowed a lot. From your point of view, nothing would have changed but, to a friend watching from far away, time around you would flow less like greased lightning and more like sap on a cold February morning. Just outside the event horizon, you would appear to stop. Since light cannot escape the event horizon, that would be the last your friend would see of you.
Gravitational time warps occur universally but are usually too feeble to be noticed. On Earth, for example, you would age one-billionth of a second less each year at sea level than you would atop Mount Everest [source: Harvard-Smithsonian].
Within a black hole, time twists even more. In fact, when we say you cant avoid falling into the singularity, it isnt just because of the intense gravity or space warping: Rather, time within a black hole warps to such a degree that the singularity literally lies in your future. Trying to prevent reaching the singularity would be like attempting to halt time.
The Day of Doom
Suppose a far-off black hole is locked in a binary embrace with a star that goes supernova. Suddenly freed, the gravitational giant shoots our way at tens to hundreds of kilometers per second. How would we know?
The short answer is, we wouldnt at least, not until it interacted with something because a black holes massive gravitation denies escape even to light. So, instead of trying to spot a peppercorn on a black carpet, lets look at a few ways we might identify a black hole indirectly.
First, matter ripped apart by a black hole emits radiation as it swirls into its accretion disk, causing the area around it to "shine" like a feather boa under klieg lights.
Second, the black holes distortion of surrounding space, if spotted by earthlings, could also render it detectable. This gravitational lensing, predicted by Einsteins general theory of relativity, has been observed by astronomers near massive objects like galaxies, black holes and our sun [sources: STSI; University of Illinois].
Even under ideal circumstances, however, spotting a black hole this way would harder than finding a flea on a speckled dog at night with binoculars. And an eye patch. For gravitational lensing to be visible from Earth, the black hole must pass between us and a star; for us to spot it, it must transverse the star, so that astronomers have a normal view to compare it to. Even if this were to happen, which is unlikely, the size of both the black hole and of the lensing effect would be so miniscule that wed be lucky to spot it even if we were looking for it [source: Unruh].
Finally, a black hole could make itself known by interacting gravitationally with celestial objects like planets, stars, asteroids or comets, which brings us to a key question: How close does our hypothetical black hole pass by our solar system?
Clearly, the closer it passes, the worse the damage. A near miss could severely perturb planetary and lunar orbits, like a sparrow slamming into a spiral spiderweb, dragging the curved orbits into a tangle of interactions.
From our perspective on Earth, the tides would change and the sky would alter. If the black holes gravity kicked our orbit farther from the sun or closer inward, or made it more elliptical, we would suffer shifts in global temperatures and seasons, or possibly worse. In the worst case (short of becoming a black hole amuse-bouche), Earth might be thrown into the sun, or sent hurtling out into space on an escape trajectory, doomed to freeze and die.
As well-known astrophysicist Neil deGrasse Tyson once told news program "20/20" with characteristic understatement, "It would be a bad day for the solar system if we got visited by a black hole. "With that in mind, lets stop dancing around the event horizon and dive right in.
The End of the World, or Through the Looking Glass
You climb into your indestructible pod, knowing it will spare you only briefly, but hoping at least to survive long enough to experience the black holes interior. Launching into space, you plot a gentle, decaying orbit inward.
Luckily for you, but unluckily for the solar system, this is a supermassive black hole. Yes, were changing the rules, but everything would happen far too quickly if we didnt.
Heres why:
In a small black hole say, around 30 solar masses the tidal forces caused by the steep intensification of gravity over distance would tear you apart long before you reached the event horizon. In fact, at the event horizon, the tidal force between your head and your feet would be around 1 million Gs (Earth gravities). Even if you could survive, there would be no time to enjoy your victory, for you would encounter the singularity 0.0001 seconds after crossing the event horizon [source: Hamilton].
In a supermassive black hole sporting the mass of 5 million suns, like the one at the center of our galaxy, the experience is much different. Any black hole that bulks up to more than 30,000 solar masses exerts head-to-toe tidal forces of less than 1 G at its event horizon. Theres also more time for sightseeing on the way to your doom: On a curved descent, it will take you 16 seconds (and change) to reach the singularity after crossing the event horizon (this "infall" time is a function of the black holes mass; the more mass, the longer it takes) [source: Hamilton].
Falling through the event horizon of a black hole is a bit like falling asleep or falling in love: Its hard to pinpoint when it happens, but once it does, your sense of reality is significantly compromised. In the case of the black hole, you can still see the starfield (light can get into a black hole, it simply cannot leave), but the view reminds you of the whorls of color inside a soap bubble, and there is something else wrong, too: The curved space-time garbles and twists light, confusing your binocular vision; its like peering through a kaleidoscope with your eyes crossed [source: Hamilton].
Tidal forces stretch your craft downward like taffy and crush inward on you from every side. As you near the singularity, you witness an extraordinary sight: The outside universe appears to compress into a bright, thin, blueshifted band around your waist, as the views above and below dim and redshift. After that, whats left of your shredded matter enters a point of infinite curvature, where known space and time end.
The Largest Black Holes in the Universe