D. Cowen
Professor of Physics and Astronomy
University of Pennsylvania
No matter can pass through a black hole. Any matter encountering a black hole gets stuck
there.

Astronomer*
Matter is accelerated toward the speed of light as it falls into a black hole. The friction between differentially accelerated packets of material causes the matter to heat up to tremendous temperatures and emit X-rays that are detectable from earth.

Douglas Scott
Professor
University of British Columbia
Presumably it gets crushed to unimaginable densities. But of course no one knows. And the point is that if it happened to you, you couldn't ever tell anyone!

Dr. Michael M. Davis
Astronomer
SETI Institute
Not much, for a massive black hole, but quite a lot for a mini-black hole. It all depends on the rate of change of gravitational pull. The turn-around point for light to get pulled back into the black hole is really quite a ways out for a massive black hole, and matter crossing the boundary doesn't feel much of anything special. But things are very different for a very low mass black hole. Here, if you were to get sucked in, your feet might feel a lot more gravity than your head, and you could get stretched out long and skinny. Even so, you might not notice, because time gets stretched out too near a black hole, so you might think you were just going through a growing spurt.

Yervant Terzian
Professor
Cornell University
We do not know. The central singularity is a puzzle.

Prof. Wayne G. Roberge
Theoretical Astrophysicist
Rensselaer Polytechnic Inst.
A black hole is surrounded by an imaginary sphere called the event horizon. For example,
a black hole with one solar mass has an event horizon 3 kilometers in radius. General
Relativity says that once matter comes closer than the event horizon it can never get back out. It will fall toward the center of the black hole, where gravity becomes infinite. Trying to use a rocket motor to get out would only cause you to reach the center faster. The trip from the event horizon to the center takes only a few microseconds for a black hole of one solar mass but would take longer for supermassive black holes.

Andrew Liddle
Astronomer
University of Sussex, UK
Who knows?!!

Karen Vanlandingham
Assistant Professor
Columbia University's Biosphere 2 Center
Anything large (such as a person) would get torn apart by gravity. After that, we don't know.

Astronomer*
It loses all its characteristics as it becomes part of the black hole.

Eilat Glikman
Graduate Student
Columbia University
Matter does not pass *through* a black hole, because it never emerges! Once it goes in it never comes out! It is utterly destroyed. Not only are the molecules broken into atoms, but the atoms are taken apart into electrons and protons, and the protons are further broken down into quarks (the tiniest building blocks - we think!).

Professor*
If the black hole is not rotating, then the mass that falls in gets added to the black hole. It loses all properties except mass, electric charge (if any) and angular momentum (if any).

Walter Harris
Astronomer
University of Wisconsin-Madison
There are two answers to your question, what happens and when does it happen?

As for *what* happens, well material falls onto a black hole just like you would fall out of a building. As you fall, you accelerate, with the rate of acceleration depending on the mass and size of the Earth. On a black hole the acceleration is SO great that you eventually will be falling at the speed of light. Don't count on getting there intact though, because long before you are moving that fast, the stresses of changing gravitational forces will first tear *you* apart and then the very atoms you are made of. At the black hole itself the stresses are so great that not even protons, neutrons, and electrons can exist.

As for when.....well here is the kicker. All of the above *will* happen, but it will take
*forever* to do it. If you have ever read about Albert Einstein's theory of relativity you will no doubt be aware of that prohibition against traveling at the speed of light. If that is true, then how can gravity accelerate you to the speed of light, but still not break the law? The answer is a concept called time dilation. It says that time passes more slowly for an object as it moves closer and closer to the speed of light. More than a few science fiction stories have been written on this topic, but in the case of a black hole it works for real. At the moment that you are approaching the speed of light time dilation will be stretching out the length of that next second so that you can't ever get there. This contradiction stops you in place. That next tick of the clock will take forever to happen. For this reason many scientists refer to black holes as Frozen Stars;.

Graduate Student*
As a person passes through the event horizon of a black hole, she wouldn't notice anything! The event horizon is only noticeable to those far from the hole. As you fall in toward the center (feet first, say) you will start to experience "tides" similar to those on
the Earth. Every part of you would be attracted to the center of the black hole with a different strength. Because the gravitational field is so strong, and the distances over which it varies are so small, your feet will feel a greater force than your head, and your arms will feel as if they are being pulled in toward your body. Basically you would be pulled like a piece of Silly Putty. Ouch! There is also some mathematical evidence that as you get closer to the center (or "singularity" as we call it) you would be rapidly pulled apart and squished up. This is, appropriately enough, called a "mixmaster model."

Professor Rex A. Saffer
Physicist, Astronomer, Educator
Dept. of Astronomy & Astrophysics, Villanova University
We really don't know. By definition, nothing that passes into a black hole can get back out because the gravity is too strong. This includes light! Since we can only know things about astronomical objects by the light they give off, if no light comes out of a black hole, then we cannot know anything about the matter inside.

Bob Mathieu
Professor of Astronomy
Department of Astronomy, University of Wisconsin - Madison
I wish I knew!

Steven Novotny
Air Force Officer/Graduate Student
University of Florida Astronomy Department
It depends on whether you are the matter or the person watching the matter. If you are
watching you will see the matter get red-shifted (becomes increasingly red and dim until you can no longer see it). Inside what is called the Schwarschild radius, an object would feel differential acceleration - the bottom would be pulled stronger than the top, and it would presumably be ripped apart.

James Pantaleone
Professor of Physics
University of Alaska Anchorage
Some people have speculated about wormholes, which are distant black holes that are connected to each other. However it is likely that these do not really exist, and that
matter that falls into a black hole just stays there and makes the black hole larger.

Steven Balbus
Astronomy Professor
University of Virginia
It is destroyed as it approaches the very center, and then disappears, leaving only its gravitational field behind.

David Batuski
Astronomer
University of Maine
Can't pass through. Once inside event horizon, it squishes into the singularity.

Astronomy Professor*
Once matter crosses the event horizon of a black hole it has disappeared from our universe. What happens to it or whether or not it can pass through the black hole is unknown. Science fiction writers have many scenarios involving black holes!

John Huchra
Astronomer/Professor
Harvard-Smithsonian
Another good question. I don't know.

*Respondents opted for anonymity and we respect their wishes.