Black holes are often misunderstood. Or mistaken for something bad.
What are they anyway? They are intensely fascinating objects in space, places where matter has been ground into an intensely compact region. If Earth were (hypothetically) crushed into a black hole, it would be less than an inch wide. Even so, the object would still be extremely massive, as it would contain the entire mass of our planet.
The result? A place with a gravity so strong that not even light can escape. (Things with more mass have a stronger attraction.)
This allows black holes to resemble omnipotent, terrifying objects, with an insatiable diet for stars and planets. But this is not so. They are not threats in the cosmos. As astrophysicist Misty Bentz told Mashable, after the first picture ever taken of a black hole: “We tend to anthropomorphize these things. But really, black holes aren’t bad, mean or scary. to be†
Below, we address misconceptions about black holes, including Sagittarius A*, the supermassive black hole at the center of our Milky Way Galaxy. Astronomers recently captured an unprecedented image of this cosmic behemoth†
A NASA illustration showing the superhot accretion disk surrounding a black hole. You can also see an energy beam released from matter outside the black hole.
Black holes have no special gravity
Nothing we know of can escape from a black hole. Something should be moving faster than the speed of light – traveling from Earth to the moon in about a second – break out. This could make it appear that black holes exert excessive gravity. But that’s not exactly the case.
“There’s nothing special about the gravity of a black hole,” Douglas Gobeille, an astrophysicist and black hole researcher at the University of Rhode Island, told Mashable.
If the sun were replaced by a black hole of the same mass, most planets would continue to move around the sun as they are now, with only the closest planets noticing. tidal forces from the black hole. And if Earth were replaced by a black hole of the same mass, the moon’s orbit wouldn’t change much either. That’s because the mass they revolve around remains the same.
But the situation is changing when something ventures near a black hole (“near” is relative and depends on the size of the black hole). The unique thing about black holes is how close something can get to the whole of such an intensely compact, massive object. If you somehow visited the surface of the sun, you still wouldn’t be right next to an object nearly the density of a black hole. For supermassive black holes, which are millions to billions of times more massive than the Sun, “relatively close” could mean 100 million miles away†
“You would feel exceptional gravity if you got close to a black hole,” Gobeille said.
The first image of Sagittarius A*, the black hole at the center of our galaxy.
Credit: Event Horizon Telescope Collaboration
Black holes don’t relentlessly suck up everything
Just because black holes can exert a powerful gravitational pull on passing objects doesn’t mean that black holes are “sucking up” things in the cosmos.
“Some people think they’re Hoovers [vacuum cleaners] in the sky,” Jean Creighton, an astronomer and director of the Manfred Olson Planetarium at the University of Wisconsin-Milwaukee, told Mashable. “Of course it isn’t.” If it did, the supermassive black hole at the center would of the Milky Way would be constantly breathing new stars, which fortunately for us is not the case. “They are not vacuum cleaners, otherwise we would be in one,” Gobeille agrees.
But matter or light that comes close can be drawn around a black hole. But only a small amount of this stuff actually falls into a black hole and is ‘consumed’ never to return.
“Black holes are terrible at eating things. They are notoriously picky eaters,” Gobeille says.
Black holes are terrible at eating things.
However, as matter gets closer to a black hole, things get intense. Objects like stars are literally stretched, or “spaghettified”, by gravity. This material collects in a ring called an accretion disk, where the material spins rapidly and is superheated to millions of degrees. (A hot accretion disk allowed astronomers to image of the very first black hole† the disk revealed the black hole.) Eventually, some of this accumulated material spirals into the black hole, but much of it is spewed back into space: the natural motion of the fast, rotating disk expels material.
It sure is a messy eating situation. “It’s quite difficult for black holes to feed efficiently,” explains Gobeille. Only about one percent of the cosmic material drawn around the Milky Way’s supermassive black hole Sagittarius A* actually falls into it, notes NASA†
But if something falls into a black hole, it means it has passed a point of no return, the ‘event horizon’. “That’s the last point,” Marco Ajello, an astrophysicist at Clemson University who studies supermassive black holes and galaxies, told Mashable. Hypothetically, he explained, a person could still use a flashlight just outside the event horizon. But once they’ve crossed over, that light can’t go back out into the universe.
“Most black holes sit there still.”
However, most black holes do not actively eat anything. That’s because they don’t look for anything out or suck in anything. Compared to the galaxies they occupy, even supermassive black holes occupy small spaces. Things have to wander by.
“Most black holes sit still there,” Ajello explained.
Black holes aren’t really holes – are they?
Black holes clearly contain an extraordinary amount of matter. They have a shape (spherical). And other matter interacts with black holes. So astrophysicists often classify them as objects, although uncommon. “It’s a fantastically weird object,” Ajello said.
Labeling a black hole as an “object” or “thing” is appropriate, Dominic Pesce, an astrophysicist at the Center for Astrophysics-Harvard and Smithsonian who studies supermassive black holes, told Mashable. And others could reasonably choose to describe them as a “region,” he noted
But if someone insists that black holes are indeed ‘holes’, they also have a reasonable argument.
“In fact, I think there’s a case for black holes being referred to as ‘holes’ in the observable universe, in the sense that they enclose a region of spacetime over which outside observers cannot gather information,” Pesce said.
An artist’s concept of a black hole. Outside the black hole, energy is released as hot matter revolves in a disk.
Black holes are not relentless cosmic vacuum cleaners with unnatural gravity. But the common belief that they are deeply creepy is absolutely real. Many aspects of black holes remain mysterious, especially their insides.
“We have no way of exploring the interior of a black hole,” explained Creighton astronomer. Researchers can only theorize what could happen therea realm where space and time would collapse.
What we know about black holes comes from how things interact with them — beyond their event horizon, of course. For example, when a black hole breaks apart or engulfs a star, the hole’s swirling disk of superheated material can glow or throw bursts of energy into space. Sometimes these invisible objects can essentially scream out into the cosmos. Us specialized telescopes and radio antennassuch as those used by the astronomers who recently imaged the black hole at the center of our galaxy, detect this energy, revealing their activity or existence.
In the coming years, these gigantic instruments will reveal more secrets about the curious black holes in our universe and capture more unprecedented images. Without them we would be in the dark.
“What people can literally see and hear in the universe is next to nothing,” Gobeille said.
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