Could a black hole or magnetar ever be close enough to Earth to swallow it whole? If so, how far away would it have to be?

Let’s clear some assumptions first. Black holes do not ‘swallow’ anything.

Black holes behave just like any other gravitating body meaning, objects fall due to the gravitational pull.

See it this way

Earth’s acceleration due to gravity is 9.8 meters per second² and so when you drop an object into a deep, open well, you see it slowly dropping and accelerating until it hits the bottom or disappears from view.

We see this all the time and are quite familiar with this.

Now, imagine, the acceleration due to gravity was 98 meters per second², when you drop an object into the same well, you will see the object moving as if it was being sucked by the well.

Then you can go on like this and imagine how the motion would be if the gravitational acceleration was 980 meters per second² and so on.

A black hole is a region with extreme gravity the acceleration considered faster than the speed of light.

“Close enough” is vague as far as black holes are concerned. Black holes have an event horizon the radius of which depends on its mass.

It is the boundary between the Black Hole and the space around it, from which matter and energy cannot escape the gravity of the Black Hole.

For example, a black hole with a million solar masses will have an event horizon with a radius of 3 million kilometers.

If Earth or any other body gets within 3 million kilometers of such a black hole (meaning, across the event horizon), it will begin interacting with the gravity of the black hole and start spiraling into it.

There is no escape. As it gets closer to the center of the black hole, the strong tidal forces will tear it apart into its component particles the body simply disintegrates and will approach the center in a stream of particles and end there, leaving nothing behind.

So, you see the Earth or any other such body does not get pulled in its original shape and size. In other words, a black hole does not ‘swallow’ Earth as a whole.

A magnetar is actually a neutron star with extreme magnetic field trillions of times stronger than Earth’s magnetic field and are second only to black holes as far as the gravity is concerned.

With the escape velocity in the range of a third of the speed of light, objects can and do escape from the gravitational pull of magnetars.

However, neutron stars and magnetars do accrete gas and dust from the surrounding region and of course, gas from stars too, if they are part of a binary or a multiple star system.

Needless to mention, if the accretion of mass reaches a critical level 2.16 solar masses then it disappears as a black hole.

Also Read👇👇👇

What is a white hole | Why white hole is compared with a black hole