Black holes aren’t bad cosmic vacuum cleaners, and other misconceptions

Black holes can often be misunderstood. Or mistaken for something wrong.

What are they, in fact? They are intensely fascinating objects in space, places where matter has been reduced to an extremely compact area. If the Earth were (hypothetically) crushed into a black hole, it would be less than an inch in diameter. Yet the object would still be extremely massive, as it would contain the entire mass of our planet.

The result? A place with such a strong gravitational pull that not even light can escape. (Things with more mass have a stronger gravitational pull.)

This can make black holes appear as omnipotent and terrifying objects, with an insatiable diet of stars and planets. But this is not the case. They are not threats in the cosmos. As astrophysicist Misty Bentz told Mashable, following the first image taken of a black hole“We tend to anthropomorphize these things. But really, black holes aren’t bad or mean or scary. They are.”

Below, we address common misconceptions about black holes, including Sagittarius A*, the supermassive black hole at the center of our galaxy, the Milky Way. Astronomers recently captured an unprecedented image of this cosmic monster.

A NASA illustration showing the super hot accretion disk around a black hole. We also see a jet of energy released from matter outside the black hole.
Credit: NASA

Black holes do not have special gravitational powers

Nothing we know can escape from inside a black hole. Something should be moving faster than the speed of light – traveling from Earth to the Moon in about a second – to escape. This could give the impression that black holes exert excessive gravitational force. But that’s not exactly the case.

“There is nothing exceptionally special about the gravity of a black hole,” Douglas Gobeille, an astrophysicist and black hole researcher at the University of Rhode Island, told Mashable.

In fact, if the Sun were replaced by a black hole of the same mass, most planets would continue their movement around the Sun as they do now, only the nearest planets noticing tidal forces of 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. This is because the mass around which they orbit remains the same.

But the situation is changing when something ventures near a black hole (“close” is relative and depends on the size of the black hole). What’s unique about black holes is how close something can get in full of such an intensely compact and massive object. If you somehow visited the surface of the sun, you still wouldn’t be immediately next to an object with 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.

“You would feel exceptional gravity if you approached a black hole,” Gobeille said.

the black hole in the center of the milky way

The first image of Sagittarius A*, the black hole at the center of our galaxy.
Credit: Collaboration with the Event Horizon Telescope

Black holes don’t suck everything up relentlessly

Just because black holes can exert a powerful gravitational pull on passing objects, doesn’t mean black holes are out there “sucking up” things in the cosmos.

“Some people think they’re Hoovers [vacuum cleaners] in the sky,” Jean Creighton, astronomer and director of the Manfred Olson Planetarium at the University of Wisconsin at Milwaukee, told Mashable. “Of course, that’s not true. “If it did, the supermassive black hole at the center of the Milky Way would be constantly sucking in new stars, which luckily for us isn’t the case.” They’re not vacuum cleaners, otherwise we’d be in one,” Gobeille agreed.

But matter or light that passes nearby can be pulled around a black hole. Yet only a small amount of this substance actually falls into a black hole and is “consumed”, never to return.

“Black holes are terrible at eating things. They’re notoriously picky eaters,” Gobeille said.

Black holes are terrible at eating things.

However, as matter approaches a black hole, things get intense. Objects like stars are literally stretched, or “spaghettified”, by gravitational pull. 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 imagine the very first black hole; the disc revealed the black hole.) Eventually, some of this accumulated substance spirals into the black hole, but much of it is thrown back into space: the rapid, rotating natural motion of the disc ejects material.

This is definitely a messy restaurant situation. “It’s quite difficult for black holes to feed efficiently,” Gobeille explained. Only about one percent of cosmic matter pulled around the Milky Way’s supermassive Sagittarius A* black hole actually falls into it, NASA remarks.

But when something falls into a black hole, it means it has passed a point of no return called the “event horizon.” “That’s the last point,” Marco Ajello, a Clemson University astrophysicist 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 have crossed over, that light can no longer escape into the universe.

“Most black holes sit there quietly.”

The majority of black holes, however, do not actively eat anything. This is because they seek nothing, nor aspire anything. Compared to the galaxies they occupy, even supermassive black holes occupy tiny spaces. Things have to pass.

“Most black holes sit there quietly,” Ajello explained.

Black holes aren’t exactly holes, are they?

Black holes clearly contain an exceptional amount of matter. They have a (spherical) shape. And other matter interacts with black holes. Thus, astrophysicists often classify them as objects, although unusual. “It’s a fantastically bizarre object,” Ajello said.

Labeling a black hole as an “object” or a “thing” is appropriate, Dominic Pesce, an astrophysicist at the Center for Astrophysics-Harvard and Smithsonian who studies supermassive black holes, told Mashable. And others might 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.

“I even think black holes should be referred to as ‘holes’ in the observable universe, in the sense that they enclose a region of spacetime over which external observers cannot glean any information,” Pesce said.

a black hole illustration

Artist’s conception of a black hole. Energy is released outside the black hole as hot matter spirals into a disk.
Credit: XMM-Newton / ESA / NASA

Black holes are not relentless cosmic vacuum cleaners with artificial gravitational powers. But the common understanding that they’re deeply weird is definitely real. Many aspects of black holes remain mysterious, especially their interiors.

“We have no way of probing the interior of a black hole,” explained astronomer Creighton. Researchers can only theorize what might happen therea realm where space and time are thought to break down.

What we know about black holes comes from how things interact with them — outside of their event horizon, of course. When a black hole shreds or consumes a star, for example, the hole’s swirling disc of superheated material can glow or eject bursts of energy into space. Sometimes these invisible objects can basically scream out into the cosmos. Our specialized telescopes and radio antennaslike those used by astronomers who recently imaged the black hole at the center of our galaxy, detect this energy, which reveals their activity or existence.

In the years to come, these giant instruments will continue to unlock more secrets about the curious black holes in our universe and capture unprecedented images. Without them, we would be in the dark.

“What humans can literally see and hear in the universe is next to nothing,” Gobeille said.

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