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Fraser
2007-Jan-29, 08:27 PM
Our episode on black holes generated many many questions from listeners. We dip into this bottomless pool of questions and start dealing with them. Are really big black holes like the Big Bang? How can black holes evaporate? What would it look like to stand on a black hole? And just how large would a rock have to be before its gravity is so strong that a human can't escape?<br />
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<a href="http://media.libsyn.com/media/astronomycast/AstroCast-070129.mp3"><strong> Episode 21: Black Hole Questions Answered (15.7 MB)</strong></a>

Read the full blog entry (http://www.astronomycast.com/questions/episode-21black-hole-questions-answered/)

Doomspiel
2007-Jan-30, 05:55 PM
Hey guys, I like the show, but I had to point out that in a sufficiently large non-active blackhole, the density and tidal forces at the schwarzschild could be quite small. If it was a sufficiently large black hole, assuming that physics keeps working past the event horizon of the black hole, a person could die of old age before the tidal forces made themselves felt. Anywho, good show, keep up the good work.

tdvance
2007-Jan-30, 06:47 PM
Hey guys, I like the show, but I had to point out that in a sufficiently large non-active blackhole, the density and tidal forces at the schwarzschild could be quite small. If it was a sufficiently large black hole, assuming that physics keeps working past the event horizon of the black hole, a person could die of old age before the tidal forces made themselves felt. Anywho, good show, keep up the good work.

In fact, I have the vaguest memories of a science fiction short story (I do not remember the title or the author) in which a spacecraft full of 40 y/o scientists dove into a large black hole in which they estimated they would survive for 30 years, on the grounds that they would enjoy 30 years of studying a black hole from the inside. (or, at least, that portion outward in relation to them). Of course, they'd never publish the results outside the event horizon....

Elliott
2007-Jan-31, 05:29 PM
You guys mentioned that if you fell into a black hole that you would be stretched out.

If the stuff that's further away from the black hole appears to be moving faster than the stuff closer to the black hole, if you were falling into the black hole, wouldn't you be compressed rather than stretched out?

Hamlet
2007-Jan-31, 06:19 PM
You guys mentioned that if you fell into a black hole that you would be stretched out.

If the stuff that's further away from the black hole appears to be moving faster than the stuff closer to the black hole, if you were falling into the black hole, wouldn't you be compressed rather than stretched out?

The stretching is due to the gravitational tidal force (http://en.wikipedia.org/wiki/Tidal_force). If you're falling feet first into a black hole, your feet are closer to the black hole than your head. Your feet will experience a higher acceleration than your head leading to the stetching out effect. In the highly complex world of astrophysics this is referred to as "spaghettification" (http://en.wikipedia.org/wiki/Spaghettification). :lol:

C0ppert0p
2007-Jan-31, 06:19 PM
Hey guys, I like the show, but I had to point out that in a sufficiently large non-active blackhole, the density and tidal forces at the schwarzschild could be quite small. If it was a sufficiently large black hole, assuming that physics keeps working past the event horizon of the black hole, a person could die of old age before the tidal forces made themselves felt. Anywho, good show, keep up the good work.

Is it at the event horizon or the singularity that the current laws of physics fail?

Is there a case for our universe being a black hole? I recall reading somewhere that there was...

When matter is caught in the inflow to an active black hole will the accretion disk grow dense enough to cause fusion as we've found in the accretion disks of white dwarfs, (dwarves?) orbiting companion stars?

How do Branes relate to black holes?

niin
2007-Feb-07, 03:20 PM
I wished they had talked about evidence for stuff some more.
Is there any evidence of matter being able to collapse it's physical structure due to gravity?
What are the evidence?

Himanshu Raj
2007-Feb-08, 09:02 AM
Hi Frazer!

In your previous show on EM Spectrum I learnt that any body in the Universe that has temperature above absolute zero it gives off radiation (wien's displacement law). Since the black hole gives off Hawking's Radiation so it must have some temperature. If it does then what range of temperatures does a black hole have?

Blob
2007-Feb-08, 01:38 PM
Hum,
it depends on the surface area but it is a lot colder than the surrounding space; it is just a tiny fraction of a degree above absolute zero.

Himanshu Raj
2007-Feb-09, 06:57 AM
Hum,
it depends on the surface area but it is a lot colder than the surrounding space; it is just a tiny fraction of a degree above absolute zero.

That's all right but there's another fact that black holes consume matter. When black holes consume matter, the matter gets superheated due to friction so much so that it gives off X-rays before falling completely into the Black Hole. Doesn't this superheated matter contributes to the temperature of the black hole which can be way beyond-well-at least a few hundered degrees above absolute Zero.

EvilEye
2007-Feb-10, 02:06 PM
I just want to know when the next show will be?

I love this stuff.

Hello folks. Newbie here.

Hamlet
2007-Feb-10, 05:52 PM
I just want to know when the next show will be?

I love this stuff.

Hello folks. Newbie here.

Welcome to the BAUT, EvilEye!

New shows are usually available on Monday's and can be found at the top of this page: Astronomy Cast (http://www.astronomycast.com/). The archive of past shows is here (http://www.astronomycast.com/archive/).

EvilEye
2007-Feb-10, 06:27 PM
Welcome to the BAUT, EvilEye!

New shows are usually available on Monday's and can be found at the top of this page: Astronomy Cast (http://www.astronomycast.com/). The archive of past shows is here (http://www.astronomycast.com/archive/).

Thank you thank you thank you!

I am going to be so busy.

I'm also subscribed to Dr. Micho Kaku's podcasts "Explorations", but half the time, they aren't even him.

This place RAWKS!

Just wondering now if there are any by Charles Sief, Brian Greene, or Phil Plait (The Bad Astronomer) - I mean podcasts.

richk
2007-Feb-15, 02:04 PM
Hi - I love the show. I've been listening since the first episode and this is exactly the kind of thing that podcasting was invented for. I teach astronomy at Hume-Fogg Academic Magnet High School in Nashville, Tennessee, and I've recommended your podcast to my students. I've got a couple of questions that occurred to me while listening to the "black holes questions" show. Do black holes suck up dark matter as well as normal matter? Do black holes interact with dark energy? Thanks again for the great show.

tdvance
2007-Feb-25, 07:17 PM
That's all right but there's another fact that black holes consume matter. When black holes consume matter, the matter gets superheated due to friction so much so that it gives off X-rays before falling completely into the Black Hole. Doesn't this superheated matter contributes to the temperature of the black hole which can be way beyond-well-at least a few hundered degrees above absolute Zero.

It contributes to the temperture of the area surrounding the black hole, but not the hole itself. The temperature of a black hole is related only to its surface area (larger area being cooler temperature). For any black hole not microscopic, it is colder than the "ambient temperature" of the universe, the latter of which being something like 2 celsius degrees above absolute zero. A stellar black hole is much, much colder than the 2 degrees. You can read about this in Hawking's "A Brief History of Time" or I'm sure it's on Wikipedia somewhere.

Ilyas
2007-Feb-26, 08:18 AM
assuming that physics keeps working past the event horizon of the black hole, a person could die of old age before the tidal forces made themselves felt.


If that were the case, that would be amazing - Don't you agree?