Imagine the Universe!
Imagine Home  |   Teachers' Corner   |  

2. It would not change.

3. The lunar orbit would take the same as it does now, ~ 27.3 days. The orbit of a spacecraft that had been hovering just over the surface of the Earth would be the same as the current rotation period of Earth, 24 hours. The fly would be inside of the event horizon...so we have no idea what is happening to it!

4. We would solve for M in the Schwarzchild equation to find M = c2R/2G. If the radius of the basketball is 17.5 cm, the necessary mass would be 1.18 x 1026 kg. This is approximately the mass of Neptune.

How Much Do You Know?

1. Black holes move around the Universe sucking up everything in sight.

A black hole is not a cosmic vacuum cleaner! A black hole has an "event horizon" which is the region from inside of which you can't escape. If an object crosses the event horizon, it will invariably hit the singularity. As long as the object stays safely outside of the horizon, it will not necessarily get sucked in. Far outside of the horizon, the gravitational field of a black hole is no different from the field surrounding any other object of the same mass. A black hole is not better than any other object at "sucking in" distant objects.

Consider this: if our Sun were suddenly replaced with a black hole of the same mass, the only thing that would change would be the Earth's temperature. The gravity we feel here on Earth from the "black hole Sun" would not change.

2. Black holes will eventually suck in all the matter in the Universe.

Not true. First, to be sucked into a black hole, you have to be near the event horizon. Far outside the event horizon, stars and planets and people are affected just as if the mass in the singularity was the mass of a burning star occupying the space of the event horizon. You see, as far as the gravitational pull on an object well outside the event horizon goes, it is only the amount of mass that is important, not how it is arranged.

Furthermore, it has been shown theoretically by Stephen Hawking that when virtual particles (undetectable quantum particles that carry gravity and light) enter the event horizon and get sucked into the singularity, they use up more energy than they have and so contribute negative energy (remember that this is a quantum process and not obvious to the minds of us mere humans) to the black hole. As a result, the mass of the singularity decreases and the black hole can eventually "evaporate" in this way.

What causes the creation of these virtual particles? Fluctuations of the electromagnetic and gravitational fields, especially prevalent near superstrong gravity sources, can create pairs of virtual particles (given this name because we can not detect them in any way as they exist in this form). Left to themselves, the pairs (a particle and its antiparticle) will move apart slightly, then back together to annihilate each other on a very short timescale. However, if the pair is created right along the event horizon, as they move slightly apart one can become trapped inside the event horizon and one left outside it. They cannot then get back together to annihilate.

Back Index Next

Download a pdf version.

If words seem to be missing from the articles, please read this.

Imagine the Universe! is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

The Imagine Team
Project Leader: Dr. Barbara Mattson
Curator: Meredith Gibb
Responsible NASA Official: Phil Newman
All material on this site has been created and updated between 1997-2014.
This page last updated: Thursday, 21-Nov-2002 11:20:10 EST