Alan Stahler: This is NOT a black hole … but it’s awfully close
The nighttime sky has always evoked mysteries. Back in the mid 1700s, the mystery was comets. You could never get a good look at a comet – they’re always fuzzy. What are they?
The sky holds other fuzzy objects, but, while comets come and go (and sometimes come again), these other fuzzballs just hang there, night after night, year after year.
Back in the 1700s, the unchanging fuzzballs did not seem so interesting, leading French astronomer Charles Messier (“Sharl mess-YAY”) to make a list of them, so astronomers could recognize them right away … and ignore them.
Today, with better telescopes, and better understanding, some of these “Messier objects” have turned out to be very interesting indeed. One such is number 87 in Messier’s catalog – M87 – in the constellation Virgo.
Toss a ball into the air. It leaves your hand fast, but, as it rises, gravity sucks energy from it, and the ball slows … stops … and falls back, down to the ground.
Toss the ball faster, and it will rise higher, but gravity will still slow it down, and pull it back to the ground.
Now toss that ball upward at 25,000 miles an hour (I never said this would be easy). Again, the ball slows down as it flies upward … slows almost to a stop … but, leaving your hand at 25,000 miles an hour, it will never stop entirely … it will never fall back to the ground … that ball is gone – that ball has escaped from Earth. Twenty-five thousand miles an hour is Earth escape velocity.
If Earth were more massive — if our planet contained more rock and heavy metal — Earth’s gravity would be stronger, and escape velocity would be greater. With enough mass, enough gravity, Earth’s escape velocity would be faster than the speed of light.
Shine a light upward, and it, too, loses energy as it fights gravity. But light does not slow down. Instead, it changes color. If it started out as high-energy blue, an intense gravitational field (way stronger than Earth’s) would shift it down to low-energy red, down to lower-energy infrared, down to lowest-energy radio waves. Finally, losing all its energy, the light would go dark.
Allowing no light at all to escape, such a super-massive Earth would be black … a black hole.
M87, the fuzzball in Virgo, is a humongous galaxy — a city of stars, like our own Milky Way, but much, much larger. M87 harbors a black hole at its center — a black hole that, placed on a teeter-totter, would need six billion stars the mass of the sun — six billion suns — to balance it.
With light unable to escape, M87’s black hole is forever invisible … so where did this image come from?
Enormous gravity turns a black hole into a cosmic vacuum cleaner: It sucks in all the dust and gas — even planets and stars — that dare to come close.
As all this matter falls into the black hole, friction and collision heat it to billions of degrees, and it glows, super-bright. It’s this light, from just above the outer edge of the black hole, that astronomers have captured, to make their image.
Like dust and gas, any light that gets too close to the black hole is sucked in – thus, the dark “shadow” in the middle of the image.
Gravity affects time: Gravity slows … time … down. In this image, we’re looking at a region of space, just outside a black hole, where time has almost … slowed … to a stop. If time has stopped, no events can take place. We’re seeing an image of the black hole’s event horizon (made by the Event Horizon Telescope Collaboration).
Gravity also messes with space. The space around the black hole is so distorted, the light we see in the uppermost part of the image actually came around, from behind the black hole.
Al Stahler enjoys sharing nature with friends and neighbors. His science stories can be heard on KVMR-FM (89.5 MHz), and he may be reached at firstname.lastname@example.org.
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