## Shop Windows to the Universe

We now offer the Cool It! card game in our Science Store. Cool It! is the new card game from UCS that teaches kids about the choices we have when it comes to climate change.

# How much (in meters) is a black hole's diameter? Where do you go if you were to be sucked down a black hole? What would happen to you?

#### The diameter of a black hole depends on the mass of the original object that becomes a black hole. By the way, before they were called black holes, they were called gravitationally completely collapsed objects. The basic idea is that the radius of a black hole is that distance from the center where the escape velocity is equal to the speed of light. This is known as the Schwarzschild Radius. It can be calculated from the following equation:R = 2*(GM/c^2) In this equation, G is the gravitational constant, M is the mass of the original object, and c is the speed of light. If the Earth became a black hole it would have a diameter of about 0.017 m, about the size of a marble. If the material in the Sun were to become a black hole, the black hole would have a diameter of about 6000 m, a little less than 4 miles. No one really knows what would happen if you were to get sucked into a black hole. In fact, if our current theories of black holes are correct, no one outside a black hole can know. The issue is that as you pass the edge of the black hole, called the event horizon, no signal transmitted by you can escape from the black hole. Therefore no information from the inside of a black hole has ever been detected by our scientists outside of a black hole. The most common speculation about what would happen to you if you were to get sucked into a black hole is that due to tidal forces, you would be stretched like a string of spaghetti until you snapped!

Submitted by John (MI, USA)
(October 13, 1997)

#### Shop Windows to the Universe Science Store!

Learn about Earth and space science, and have fun while doing it! The games section of our online store includes a climate change card game and the Traveling Nitrogen game!

## What are the retrograde motions of planets in the sky?

It depends on what kind of motion you are talking about. When seen from the north pole of the celestial sphere all planets orbit around the Sun in a counter-clockwise or direct path. Most planets also...more

## How do Astronauts Live in Space?

Almost everyone has a question or two about living in space. What do astronauts do in space? How do they do everyday things like eat, sleep and go to the bathroom? Well, this is our attempt to answer...more

## How far is the Earth from the Sun, the Moon and all the other planets? How far are all of the planets from the Sun? Do you know of a software that tracks the planets in real-time?

There is a really neat internet program called Solar System Live that shows the position of all of the planets and the Sun for any given day. If you go to that page, you'll see an image similar to the...more

## Is it really true that man never really walked on the Moon?

The picture of the American Flag (the one put there by the Apollo astronauts) is waving (or straight out) in the wind. How could that be possible if there is no atmosphere on the Moon? Was it some sort...more

## How many planets orbit the sun?

I was wondering if there is a new planet? Are there planets (a tenth planet?) after Pluto belonging to our solar system? What are the names of the new planets discovered in the solar system? Are there...more

## According to Stephen Hawking, any object with an energy which equals Plank's energy has to become a black hole.

If that is so, the energy released during the Big Bang must have created many such black holes. Therefore most of the Energy of the Big bang must have disappeared in that form. Then how did the Universe...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information.