Black holes are some of the strangest and most fascinating objects in outer space.
They're extremely
dense, with such strong gravitational attraction that even light cannot escape their grasp if it comes near
enough.
So far, astronomers have identified three types of black holes: stellar black holes, supermassive black
holes and intermediate black holes.When a star burns through the last of its fuel, the object may
collapse, or fall into itself. For smaller stars (those up to about three times the sun's mass), the new core
will become a neutron star or a white dwarf. But when a larger star collapses, it continues to compress
and creates a stellar black hole. Black holes formed by the collapse of individual stars are relatively
small, but incredibly dense. One of these objects packs more than three times the mass of the sun into
the diameter of a city. This leads to a crazy amount of gravitational force pulling on objects around the
object. Stellar black holes then consume the dust and gas from their surrounding galaxies, which keeps
them growing in size.
What do black holes look like?
Black holes have three "layers": the outer and inner event horizon, and the singularity.
The event horizon of a black hole is the boundary around the mouth of the black hole, past which light
cannot escape. Once a particle crosses the event horizon, it cannot leave. Gravity is constant across the
event horizon. The inner region of a black hole, where the object's mass lies, is known as its singularity,
the single point in space-time where the mass of the black hole is concentrated.
Scientists can't see black holes the way they can see stars and other objects in space. Instead,
astronomers must rely on detecting the radiation black holes emit as dust and gas are drawn into the
dense creatures. But supermassive black holes, lying in the center of a galaxy, may become shrouded by
the thick dust and gas around them, which can block the telltale emissions.
Weird facts about black holes
If you fell into a black hole, theory has long suggested that gravity would stretch you out like
spaghetti, though your death would come before you reached the singularity. But a 2012 study
published in the journal Nature suggested that quantum effects would cause the event horizon to
act much like a wall of fire, which would instantly burn you to death.
Black holes don't suck. Suction is caused by pulling something into a vacuum, which the massive
black hole definitely is not. Instead, objects fall into them just as they fall toward anything that
exerts gravity, like the Earth.
Black holes remain terrific fodder for science fiction books and movies. Check out the movie
"Interstellar," which relied heavily on Thorne to incorporate science. Thorne's work with the movie's
special effects team led to scientists' improved understanding of how distant stars might appear
when seen near a fast-spinning black hole.A black hole isn't actually a hole. If anything, it's the
opposite. A black hole is a place in space containing a lot of stuff packed very closely together. It has
accumulated so much mass — and therefore gravity — that nothing can escape it, not even light.
And if light cannot escape a black hole, then neither can you.
As you approach a black hole, its gravitational pull gets stronger. That's true of anything with gravity,
including the Earth and sun.
Luckily, you don’t have to fall into a black hole to learn about this cosmic phenomenon.
Decades of study from a safe distance have taught scientists quite a lot. Those observations,
including startling discoveries made in recent months, continue to add to our understanding
of how black holes help shape the universe.
How to build a black hole
The gravitational pull of an object depends on how much stuff it contains. And just as with
stars and planets, more stuff — or mass — comes with a greater force of attraction.
Black holes aren’t just massive. They're dense, too. Density is a measure of how tightly mass
is packed into a space. To understand how dense a black hole can be, imagine you could
pack your own. Start with a thimble. Fill it with all of your books (you would need to really
stuff them in). Add your clothes and any furniture in your room. Next, add everything else in
your house. Then throw in your house too. Make sure to squeeze it all down to fit.
Don’t stop there: A black hole with a thimble-sized event horizon contains as much mass as
the entire Earth. Stuffing your thimble increases its density, its mass and its gravitational
attraction. The same is true with black holes. They pack a huge amount of mass into an
incredibly small space.
What the black hole wouldn't be able to do is gobble up the planets. That sort of idea gives
black holes a bad rap, says Ryan Chornock. He is an astronomer at the Harvard-Smithsonian
Center for Astrophysics in Cambridge, Mass.
“One popular misconception you see in science fiction is that black holes are kind of cosmic
vacuum cleaners, sucking in things that pass by,” Chornock says. “In reality, black holes just
sit there unless something extraordinary happens.”
Scientists can't directly observe black holes with telescopes that detect x-rays, light, or other forms of
electromagnetic radiation. We can, however, infer the presence of black holes and study them by
detecting their effect on other matter nearby. If a black hole passes through a cloud of interstellar
matter, for example, it will draw matter inward in a process known as accretion. A similar process can
occur if a normal star passes close to a black hole. In this case, the black hole can tear the star apart as it
pulls it toward itself. As the attracted matter accelerates and heats up, it emits x-rays that radiate into
space. Recent discoveries offer some tantalizing evidence that black holes have a dramatic influence on
the neighborhoods around them - emitting powerful gamma ray bursts, devouring nearby stars, and
spurring the growth of new stars in some areas while stalling it in others.
One Star's End is a Black Hole's Beginning
Most black holes form from the remnants of a large star that dies in a supernova explosion. (Smaller
stars become dense neutron stars, which are not massive enough to trap light.) If the total mass of the
star is large enough (about three times the mass of the Sun), it can be proven theoretically that no force
can keep the star from collapsing under the influence of gravity. However, as the star collapses, a
strange thing occurs. As the surface of the star nears an imaginary surface called the "event horizon,"
time on the star slows relative to the time kept by observers far away. When the surface reaches the
event horizon, time stands still, and the star can collapse no more - it is a frozen collapsing object.
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