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Thread: Brain Busters

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    Administrator Krupski's Avatar

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    Brain Busters

    In the spirit on the "Jet on a treadmill" physics comedy, I thought it would be fun to watch you Fizzy-Cysts grapple with a new concept, so here goes...

    A black hole, a star that has the mass of one million of our sun has collapsed into a sphere the diameter of earth. It's mass and gravity are beyond comprehension. Now (take my word for it), a spacecraft can orbit ANYTHING if it has enough velocity.

    So, assuming that the hellish radiation caused by matter falling into the black hole's event horizon does not penetrate your spacecraft, what do YOU see, feel or hear when you are in your ship, orbiting the black hole at a reasonable altitude (say, 1 AU* from the center of the black hole)?

    Bonus question: Assuming you cannot be hurt in any way, say you fell toward the black hole and got stuck at the event horizon. As you look around, what do you see? More detail = more points.

    Have fun, and more brain busters are upcoming!

    (* 1 AU = 93 million miles... the distance from our sun to the earth)

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    Senior Member whiskeyman's Avatar

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    Krupski you forgot to include the direction of rotation.

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    Senior Member Full Otto's Avatar

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    For peace of mind, resign as general manager of the universe

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    Team GunsNet Silver 12/2011 N/A's Avatar

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    I read somewhere that the larger the mass of a black hole, the farther from the mass is the event horizon. This being that the event horizon is a measure of gravity; nothing to do with the mass.
    Thus, the farther the event horizon is away from the mass, the less "stretching" gravity will do on a mass at the event horizon. It's entirely possible that a person or ship would experience no abnormal "stretching" at the event horizon of a massive black hole, if the gravity puts the event horizon far enough away from the mass itself.

    Now, if your black hole contains a mass the size of Earth, then it would be an enormous "singularity", so to speak, and the event horizon would be quite a long way from the mass.

    If the mass and event horizon together were no bigger than Earth, it would be a small singularity, with a very close event horizon, and you'd get stretched and tore to pieces just by coming close to the event horizon.

    Redefine your question giving us the info if you are talking about the mass being the size of Earth, or the event horizon being the size of Earth.
    Last edited by N/A; 11-05-2019 at 09:10 AM.
    No enemy of America would have ever been killed if they didn't show up to be killed. HDR

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    Team GunsNet Silver 12/2011 N/A's Avatar

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    Quote Originally Posted by Full Otto View Post
    I'm thinking you are telling us that witches have black holes?

    I know they have cold tits...or was that bitches?
    Damn, now I can't remember.
    No enemy of America would have ever been killed if they didn't show up to be killed. HDR

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    Senior Member NAPOTS's Avatar

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    I only studied newton physics so I can only offer a guess. I assume this distance is outside of the event horizon. I understand that if you were inside it even light speed wouldn't be enough to maintain orbit.

    At the cg of your space craft you'd sense 0 g because your gravitational forces are in equilibrium but your probably going so fast that time slows down for you on the side facing away from the black hole you'll see things happen that normally take eons. Supernova, formation of new stars celestial objects moving at impossible speeds. You'll probably witness objects either being drawn into ar at least pulled toward the black hole. On the side of the black hole you'll see nothing. There might also be some strange gravity affects due to the massive difference in gravity between the parts of the craft, and you, that are closer to the center.

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    Senior Member NAPOTS's Avatar

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    If I did it right you need to be going 2.98E7 m/s
    Last edited by NAPOTS; 10-15-2019 at 03:47 PM.

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    Administrator Krupski's Avatar

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    Quote Originally Posted by N/A View Post
    I read somewhere that the larger the mass of a black hole, the farther from the mass is the event horizon. This being that the event horizon is a measure of gravity; nothing to do with the mass.
    Thus, the farther the event horizon is away from the mass, the less "stretching" gravity will do on a mass at the event horizon. It's entirely possible that a person or ship would experience no abnormal "stretching" at the event horizon of a massive black hole, if the gravity puts the event horizon far enough away from the mass itself.

    Now, if your black hole contains a mass the size of Earth, then it would be an enormous "singularity", so to speak, and the event horizon would be quite a long way from the mass.

    If the mass and event horizon together were no bigger than Earth, it would be a small singularity, with a very close event horizon, and you'd get stretched and tore to pieces just by coming close to the event horizon.

    Redefine your question giving us the info if you are talking about the mass being the size of Earth, or the event horizon being the size of Earth.
    Sorry about the confusion. I just meant to say that the black hole is ginormously massive. The astronaut is in a stable orbit millions of miles above the event horizon with an eccentricity of nearly zero (i.e. almost perfectly circular).

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    Administrator Krupski's Avatar

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    Quote Originally Posted by NAPOTS View Post
    If I did it right you need to be going 2.98E7 m/s
    You would need to know the mass of the black hole and the orbiting object's altitude above the center of mass to be able to calculate the orbital velocity. Therefore, your "calculation" result of "the speed of light" cannot be correct since you didn't have the data needed to solve for it.

    Additionally, you are off by an order of magnitude. Light speed is 2.997e8 m/s., not ..e7

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    Administrator Krupski's Avatar

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    Quote Originally Posted by N/A View Post
    I'm thinking you are telling us that witches have black holes?

    I know they have cold tits...or was that bitches?
    Damn, now I can't remember.
    I think he meant "black ho".

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    Administrator Krupski's Avatar

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    Quote Originally Posted by NAPOTS View Post
    I only studied newton physics so I can only offer a guess. I assume this distance is outside of the event horizon. I understand that if you were inside it even light speed wouldn't be enough to maintain orbit.

    At the cg of your space craft you'd sense 0 g because your gravitational forces are in equilibrium but your probably going so fast that time slows down for you on the side facing away from the black hole you'll see things happen that normally take eons. Supernova, formation of new stars celestial objects moving at impossible speeds. You'll probably witness objects either being drawn into ar at least pulled toward the black hole. On the side of the black hole you'll see nothing. There might also be some strange gravity affects due to the massive difference in gravity between the parts of the craft, and you, that are closer to the center.
    Very good. Your answers are correct. Now, tell me WHY there would be "massive differences" in gravity in places away from the center of mass.

    And you did great describing how outside events, to you, would be greatly sped up.

    Have you ever heard the "whoop" sound of the gravity waves created by two colliding black holes?

    https://m.youtube.com/watch?v=QyDcTbR-kEA

    Incredible to realize that the last few milliseconds of the collision the two black holes are orbiting each other tens of thousands of times PER SECOND!

    Same thing with millisecond pulsars... something with the mass of hundreds to thousands of times the mass of our sun rotating at hundreds of times per second, creating an audio tone in a radio telescope!

    The fastest one known so far rotates at 716 revolutions per second or 42960 RPM!!! and creating an audio tone near F sharp in octave 5!!!

    A super dense ball of matter around the diameter of earth spinning at almost 43 THOUSAND RPM and with so much gravity that remains almost spherical and doesn't fly apart. Mind blowing!

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    Senior Member NAPOTS's Avatar

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    Quote Originally Posted by Krupski View Post
    You would need to know the mass of the black hole and the orbiting object's altitude above the center of mass to be able to calculate the orbital velocity. Therefore, your "calculation" result of "the speed of light" cannot be correct since you didn't have the data needed to solve for it.

    Additionally, you are off by an order of magnitude. Light speed is 2.997e8 m/s., not ..e7
    The speed I quoted is not the speed of light. I calculated it based on the givens in the problem statement; you said the black hole had the mass of 1E6 Suns and the orbit was 1 AU.

    I assumed that the effect of the earth diameter of the black hole was negligible given the size of the orbit because I am lazy.

    You'd be orbiting this sum bitch every 8.76 hours.

    gravitational field at your CG would be 5,931 m/s^2 or 605 times earth gravity. I think I was wrong on the difference in gravity, the radius is too large for 1 or two meters to matter.

    I think I was also wrong on the time dilation, you are hauling ass for sure but your Lorenz factor is only 1.005 so nothing to write home about. Time dilation due to gravitational field is also pretty small at 1.01.

    So in reality, looking away from the black hole space wouldn't look any different. Looking toward the black hole would still be black. you would see light bend around the event horizon, gravitational lensing, which would be cool! If I understand right it would look like the black hole has a halo.
    Last edited by NAPOTS; 10-17-2019 at 12:00 AM.

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    Team GunsNet Silver 12/2011 N/A's Avatar

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    Researching this, a black hole with the mass of one hundred million suns would be a super massive black hole. It's event horizon would be so far above the mass, that you would not experience any stretching at or above the event horizon. The stretching would not begin until well below the event horizon.

    The diameter of the event horizon would be on the order of hundreds of thousands of kilometers. At a distance of 1AU from the center of the black hole, you would be outside the event horizon and not experience or see anything unusual.

    What you are trying to set up is a stellar black hole, which begins at a mass 3 times our sun up to a mass of 10,000 of our sun.
    That places the event horizon much closer to the mass and has the effects outside the event horizon that you are asking about.

    A black hole with the mass of 5 of our suns would tare you apart well before you got to the event horizon.
    A black hole of one hundred million suns and you would feel no change even at the event horizon.

    Reset your values to a stellar black hole and start again.

    Last edited by N/A; 11-04-2019 at 08:44 PM.
    No enemy of America would have ever been killed if they didn't show up to be killed. HDR

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    Senior Member NAPOTS's Avatar

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    Quote Originally Posted by N/A View Post
    Researching this, a black hole with the mass of one hundred million suns would be a super massive black hole. It's event horizon would be so far above the mass, that you would not experience any stretching at or above the event horizon. The stretching would not begin until well below the event horizon.

    The diameter of the event horizon would be on the order of hundreds of thousands of kilometers. At a distance of 1AU from the center of the black hole, you would be outside the event horizon and not experience or see anything unusual.

    What you are trying to set up is a stellar black hole, which begins at a mass 3 times our sun up to a mass of 10,000 of our sun.
    That places the event horizon much closer to the mass and has the effects outside the event horizon that you are asking about.

    A black hole with the mass of 5 of our suns would tare you apart well before you got to the event horizon.
    A black hole of one hundred million suns and you would feel no change even at the event horizon.

    Reset your values to a stellar black hole and start again.
    agreed, the Schwarzschild radius of the black hole is 2.95E9 m or 1/50th of our 1 AU orbit.

    It would only have an angular diameter of around 1 degree from your point of view so it would be about as wide as your pinky with your arm outstretched.
    Last edited by NAPOTS; 10-17-2019 at 12:42 AM.

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    Administrator Krupski's Avatar

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    Quote Originally Posted by NAPOTS View Post
    The speed I quoted is not the speed of light. I calculated it based on the givens in the problem statement; you said the black hole had the mass of 1E6 Suns and the orbit was 1 AU.

    I assumed that the effect of the earth diameter of the black hole was negligible given the size of the orbit because I am lazy.

    You'd be orbiting this sum bitch every 8.76 hours.

    gravitational field at your CG would be 5,931 m/s^2 or 605 times earth gravity. I think I was wrong on the difference in gravity, the radius is too large for 1 or two meters to matter.

    I think I was also wrong on the time dilation, you are hauling ass for sure but your Lorenz factor is only 1.005 so nothing to write home about. Time dilation due to gravitational field is also pretty small at 1.01.

    So in reality, looking away from the black hole space wouldn't look any different. Looking toward the black hole would still be black. you would see light bend around the event horizon, gravitational lensing, which would be cool! If I understand right it would look like the black hole has a halo.
    Ah... my bad. When I saw the familiar 2.99 thing I thought you were just joking and used the speed of light as the velocity.

    I think looking around from orbit, you should notice:

    * The universe running at high speed (you could see stars drifting, galaxies moving and rotating, stars being born, living, then fading out or going nova.
    * A significant red or blue shift of all the universe you could see (not sure if it would be red or blue shift).

    A few thoughts... would light appear, to you, to be moving faster than 2.99e8 due to time dilation?

    What is the event horizon? If at that point the escape velocity equals c, then it means anything falling into the black hole should reach c at the event horizon, it's mass going to infinity and therefore it's velocity to zero. This seems to imply that the event horizon is a shell of matter consisting of zero thickness and infinite density, no matter how much stuff falls in, the event horizon cannot change in any way because it already is zero thickness and infinite density... it has nowhere to change into!

    A "Dyson Sphere" should be impossible to build (or at least impossible to keep it stable). If the sphere moved even a microscopic distance relative to the star, the closest point would be attracted by gravity more at the closest point (and at the same time the antipode would be attracted less and the sphere would move the closest point towards the star until the inner surface of the sphere contacted the star! To be stable the sphere would need to be built around a hypothetical star with "negative gravity" (i.e. repels rather than attracting).

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    Senior Member NAPOTS's Avatar

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    Quote Originally Posted by Krupski View Post
    Ah... my bad. When I saw the familiar 2.99 thing I thought you were just joking and used the speed of light as the velocity.

    I think looking around from orbit, you should notice:

    * The universe running at high speed (you could see stars drifting, galaxies moving and rotating, stars being born, living, then fading out or going nova.
    * A significant red or blue shift of all the universe you could see (not sure if it would be red or blue shift).

    A few thoughts... would light appear, to you, to be moving faster than 2.99e8 due to time dilation?

    What is the event horizon? If at that point the escape velocity equals c, then it means anything falling into the black hole should reach c at the event horizon, it's mass going to infinity and therefore it's velocity to zero. This seems to imply that the event horizon is a shell of matter consisting of zero thickness and infinite density, no matter how much stuff falls in, the event horizon cannot change in any way because it already is zero thickness and infinite density... it has nowhere to change into!

    A "Dyson Sphere" should be impossible to build (or at least impossible to keep it stable). If the sphere moved even a microscopic distance relative to the star, the closest point would be attracted by gravity more at the closest point (and at the same time the antipode would be attracted less and the sphere would move the closest point towards the star until the inner surface of the sphere contacted the star! To be stable the sphere would need to be built around a hypothetical star with "negative gravity" (i.e. repels rather than attracting).
    Gravitational and velocity time dilation measurable but will appear insignificant to the observer. You should see red shift and blue shift depending on which direction you are looking, into, or against rotation.

    You cannot observe light going faster than the spec of light hence relativity.

    Just because light cannot escape the event horizon does not mean everything inside of it is moving at the speed if light. By no one really knows what goes on inside a black hole because it cannot be observed. To the observer office of the black hole it no longer exists. You will notice an increase in the gravitational field fin the observed mass if it is large enough. This will be radiated back into space over eons
    Last edited by NAPOTS; 10-17-2019 at 12:30 PM.

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    Senior Member JTHunter's Avatar

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    Gentlemen - from the various articles I've read and shows I've watched about black holes, even if you are in a stable orbit around a BH, the difference in gravity between your head and your feet is measurable, even if you can't feel it. The closer you are to the event horizon, the stronger the gravity. Like light and radio waves, gravity follows the "inverse square law" where doubling the distance cuts the power by 4. Ergo, at distance of "1R", the effect is "1". Doubling the distance to "2R" cuts the effect to "1/4" of the original.
    Look at what is happening with the stars at/near the center of the Milky Way. That is where "Sagittarius A" (Sag. A) is the super-massive BH that holds sway here. Some of those stars are circling Sag. A at hundreds of thousands of MPH but, because of that speed, they are not in imminent danger of falling into Sag. A. Yes, they will eventually fall in but not likely for thousands of years, possibly millions.
    “I have little patience with people who take the Bill of Rights for granted. The Bill of Rights, contained in the first ten amendments to the Constitution, is every American’s guarantee of freedom.” - - President Harry S. Truman, “Years of Trial and Hope”

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    Senior Member NAPOTS's Avatar

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    Quote Originally Posted by JTHunter View Post
    Gentlemen - from the various articles I've read and shows I've watched about black holes, even if you are in a stable orbit around a BH, the difference in gravity between your head and your feet is measurable, even if you can't feel it. The closer you are to the event horizon, the stronger the gravity. Like light and radio waves, gravity follows the "inverse square law" where doubling the distance cuts the power by 4. Ergo, at distance of "1R", the effect is "1". Doubling the distance to "2R" cuts the effect to "1/4" of the original.
    Look at what is happening with the stars at/near the center of the Milky Way. That is where "Sagittarius A" (Sag. A) is the super-massive BH that holds sway here. Some of those stars are circling Sag. A at hundreds of thousands of MPH but, because of that speed, they are not in imminent danger of falling into Sag. A. Yes, they will eventually fall in but not likely for thousands of years, possibly millions.
    g(r)=GM/r^2

    r = 1.496E11 m

    The difference of 2 meters between your feet and your head won't even show up as a significant figure at that distance.

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