Through a hole darkly

Ready for this? Black holes. I’ve got some nifty Gif images. And this stuff is easier to understand than the last couple topics (at least for me).

Fig. 1 A simulated black hole over a starry
background. Background stars behind and
near the line-of-sight become a blended
ring caused by gravitational lensing.
(Courtesy NASA)

Believe it or don’t, the first recorded mention of even the possibility of a black hole-like body dates all the way back to 1783. English geologist John Michell described the light-absorbing properties such a body might possess. Keep in mind that this was only 50-some years after Isaac Newton died, and he was the one who first described gravity. Surprised the heck out of me. Here I’d been thinking it dated back only to the 1979 Walt Disney movie.

French mathematician Pierre-Simon Laplace suggested similar star-body properties in 1796, but the notion was then shelved through much of the 1800s.

It wasn’t until shortly after Albert Einstein proposed his theory of general relativity in 1915, suggesting the physics for such an occurrence, that the concept was revived. German physicist Karl Schwarzschild and Dutch physicist Johannes Droste, working independently, developed specific formulas that would begin to define the nature of the body which could overcome the speed of light by an extraordinarily intense gravity field.

Fig. 2  Simplified model of a black hole,
cut away to show the event horizon (A)
and the singularity (B). Outside of the
event horizon light (red arrows) can
move in any direction, but within the
event horizon, the singularity's gravity
pulls light, and everything else, inward.

Because such a body, conceptualized as a single point, has the unusual effect of altering normal light and gravitational rules, it is called a singularity, in other words, a single point unlike anything else. In fact, things become so singular that time actually may stop in a black hole. The term singularity also is used because, with neither light nor anything else able to escape, nothing can be known about these bodies through direct observation.

Another significant term defining the anatomy of a black hole is event horizon. This describes the edge or surface of the spherical area surrounding the singularity at which limit gravity overcomes the speed of light; the singularity itself is the "core" of a black hole while the event horizon is its outermost "skin." Think of it like the outer edge of the atmosphere around the earth. For a black hole singularity, this surface is described as an event horizon because, once you pass it, everything changes (not necessarily in a fun way).

Fig. 3  Plasma jets erupt from the super-

energized accretion disk as it meets the

event horizon. (Courtesy NASA)

As all this implies, the singularity is called a black hole because it sucks in all light that comes within its event horizon, leaving no way to directly observe it. Technically, it’s invisible, though there are a few ways to “see” one. We’ll get to that later.

What causes a black hole?

In a nutshell, a whole lot of particulate matter squeezed down into a very, very, very small space. The most common are probably collapsed stars, though theoretical physicists suggest several sources. Again, more on that after a bit.

If you took our sun (Hey, who can tell me our sun’s stellar name? Answer next week.), if you take our sun (about 1.4 million miles across) and crush it down until it could fit into the Grand Canyon (which is 1 mile deep), the sun would become a black hole (the Grand Black Hole?). All of the matter in the sun would be packed together so densely that it would have a gravitational field that even light couldn’t escape. And since nothing can travel faster than light, I’d stay away from the Grand Black Hole, if I were you.

In reality, though, our sun does not contain enough mass to develop the force of the collapse necessary to become a black hole. It may take a star with up to 20 times the mass of the sun to collapse into a singularity.

Fig. 4  A small star (L) has its stellar matter
drawn into the accretion disk of a nearby
black hole (R)  (Courtesy **)

Where do black holes come from?

The more popular theories suggest four types of singularities.

1. Super-massive black holes (SMBH), which occupy the center—and likely help form—most spiral galaxies like our own. An SMBH continuously draws stellar material into itself, always enlarging from the mass of the material it accumulates. The source of SMBHs is uncertain. One theory suggests they are the result of colliding masses of stars, such as head-on galaxy smash-ups (they happen). An SMBH can have as much mass as several million to several billion stars the size of our sun (our sun = 1 “solar mass”).
2. Stellar black holes are formed after an aging star uses up all of its expansive energy-producing matter—sometimes exploding in a supernova in its death throes—while all of its remaining matter collapses in on itself. Stellar black holes may contain five to twenty times the mass of our sun (5 to 20 solar masses, opinions vary) compressed into a single point (don’t try this at home).
3. A highly theoretical type (though evidence of their existence is mounting) is the intermediate mass black hole (IMBH), perhaps containing 100 to 1000 solar masses. Their existence is the hardest to explain; the jury is still out.
4. Micro or miniature black holes, possibly formed from colliding material right after the Big Bang, may be smaller than an atom but contain the same amount of mass as Mount Everest; also highly theoretical.

Fig. 5  Simulation of "Einstein Ring" gravitational lensing as a black hole

passes in front of a distant galaxy. (Courtesy **)

Here are some methods by which we can detect black holes.

Stellar black holes, SMBHs and IMBHs are surrounded by flattened accretion disks (picture track and field’s throwing discus) made up of the accumulated stars, stellar gas and dust, or other cosmic material being drawn toward the singularity at its center. This material becomes more and more compressed, and thus hotter and hotter, as it approaches the event horizon. Accretion disks are easily observable and are a primary indicator of a singularity. (Examples, Figs. 4 & 6)

As the accreted material, now energized in the extreme, approaches the event horizon, it can throw off visible plasma jets perpendicular to itself and along the line of the polar axis of the spinning singularity, another way black holes can makes themselves known. (Examples, Figs. 3 & 6)

Black holes cause gravitational lensing, a topic mentioned, in passing, in an earlier essay. This distortion of light passing near the event horizon is caused by the singularity's intense gravity. It can help in the detection of a black hole that is viewed against other cosmic background objects. (Examples, Figs. 1 & 5)

Stellar black holes may give themselves away when their gravitational allure causes a nearby star to enter an off-center orbital dance that betrays the singularity’s presence. The singularity may also be seen to draw stellar gas away from the partner star toward itself. (Example, Fig. 4)

Fig. 6  Approaching an SMBH (super-
massive black hole) of the type thought
to be at the center of  many galaxies
like our own. Note the doughnut-shaped
"torus", a bulging accumulation of
material near the center of the accretion
disk, and the plasma jets. (Courtesy NASA)

What would a visit to a black hole be like?

On the bright side, death would be instantaneous. The event horizon is not a friendly place for carbon-based life forms—or much else. Things would happen so fast that there wouldn’t be time to notice; actually, there may not be time in any form. It’s been suggested that, as your body crossed the event horizon, it would be sucked immediately toward the singularity in a long string of individual atoms, though some particles might first be thrown off at the event horizon into the hot plasma jets—to be shot a hundred light years into intergalactic space. The rest of you would be smashed into unrecognizable sub-atomic smithereens, melding none-too-gently into the ultra-solid mass of the singularity. So you probably won’t need a sweater.

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