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Littlemews
2003-Nov-26, 04:15 AM
Is that ture, there is a black hole in the middle of our MilkyWay? and now its dead? but 10 trillion yrs later it might reactive again?

imported_Jerry
2003-Nov-26, 05:06 AM
It is there and it is not dead, most think it is like a big vacume sucking everything up but it only pulls something in that gets to close, there are stars orbiting around the SMBH and they are not going to get pulled in any time soon,kinka like our planets orbiting around the sun are not getting sucked in

Littlemews
2003-Nov-26, 05:45 AM
In that case, we are safe hmm...

Haglund
2003-Nov-26, 09:11 AM
It is said to be an enormous black hole at the centre of the Milky Way, perhaps as massive as 2 million Sol masses.

http://antwrp.gsfc.nasa.gov/apod/ap021018.html

imported_Draco
2003-Nov-26, 11:33 AM
The black hole in the centre is dead? What? I never knew that?
I just know that there are 3 types of black holes. Mini black holes, formed at the big bang, stellar black holes, formed when a massive star collapses and super massive black holes, found at the centre of galaxy’s or the galactic bulge or nucleus.

imported_Jerry
2003-Nov-27, 04:16 AM
Micro black holes

Jerry
http://doctorlock.net

imported_Jerry
2003-Nov-27, 04:20 AM
Super massive black holes SMBH are still in debate as to how they were formed so I have not read too many reports that say how but only so many different POSSIBLE scenarios. I guess in fear of being wrong.
Some ideas are from the big bang theory with space expanding outward creating micro or seed black holes that have been growing over time capturing clouds of gas and matter forming stars then finally galaxies.
Some other reports state that a galaxies own core collapses under its own immense gravity, making the SMBH themselves. This theory has the core creating the SMBH much in the same manner as a giant stars core collapsing, making a black hole I hope this helps you some.

Littlemews
2003-Nov-27, 06:14 AM
Hmm somehow I really wanna see what's inside the black hole. Well for most of the theories saids, when u inside the blackhole, you are gone and disppear in this world (Universe).... but its only a guess...but is there some kinda different energy can go through there and come back safely...Light cant Survivor hmm what kinda energy that travel fast than light anyway? Well in this Universe, everything exist, so just think @_@

What about Darkness...j/k!

Very Curious
2004-May-07, 08:38 PM
So what would happend if you actually went inside a blackhole?

Tiny
2004-May-07, 10:25 PM
3 answer :
1. You are gone and enter a different universe..
2. The mass of gravity squzze you into a tiny particles
3. You are alive and found alot of golds and diamonds inside...j/k

John
2004-May-07, 10:55 PM
I'll take #3, Tiny, but I think #2 is probably the correct answer.

I think you'd be crushed into the singularity, and actually become a single particle with the mass of everything that has entered the black hole.

StarLab
2004-May-08, 01:43 AM
I agree with you, John.

But if objects get pulled into the SMBH only when they get really close, then howcome the SMBH has a deadlock on the rest of the galaxy if it ain&#39;t gonna suck up it all in? :o <_< :rolleyes: ;) :huh:

Tiny
2004-May-08, 01:54 AM
Black hole they actually don&#39;t suck stuff easily... but if you within 3Rs from the black hole you will be suck in... a star form between the distance of 3Rs of BH or SMBH they still can survive and orbiting the black hole...

John
2004-May-10, 01:46 PM
Originally posted by StarLab@May 8 2004, 01:43 AM
I agree with you, John.

But if objects get pulled into the SMBH only when they get really close, then howcome the SMBH has a deadlock on the rest of the galaxy if it ain&#39;t gonna suck up it all in? :o <_< :rolleyes: ;) :huh:
The Oort Cloud cometary bodies are 10,000 to 50,000 astronomical units from the Sun, but they still orbit the Sun. You don&#39;t have to be close to an object to be gravitationally bound to it.

tony873004
2004-May-10, 04:11 PM
The super massive black hole (SMBH) at the center of the galaxy contains only a very small fraction of a percentage of the mass that our solar system, and most of the rest of the galaxy orbit. So the SMBH is not really analogous to the central star of a star system. Earth would orbit the Sun just fine if Mercury and Venus disappeared. But our solar system would escape the galaxy if all the galaxy&#39;s mass interior to us other than the SMBH disappeared.

However, I still think that the SMBH is important in holding the galaxy together. There needs to be something significantly more massive than anything else to serve as an anchor. I don&#39;t think the stars in the central buldge of the galaxy could just orbit their common center of mass without all the stars eventually escaping. I tried simulating globular clusters, and I couldn&#39;t get any of them to stay together unless one member was significantly more massive than the others. They probably have a black hole too.

StarLab
2004-May-10, 04:20 PM
So how can a BH have such a strong grip, yet it only sucks in what&#39;s nearest to it? If the galaxy lasted a bit longer, would the sun eventually be pulled into the middle, waiting in line for its ticket to the BH?

John
2004-May-10, 04:33 PM
Originally posted by tony873004@May 10 2004, 04:11 PM
However, I still think that the SMBH is important in holding the galaxy together. There needs to be something significantly more massive than anything else to serve as an anchor. I don&#39;t think the stars in the central buldge of the galaxy could just orbit their common center of mass without all the stars eventually escaping. I tried simulating globular clusters, and I couldn&#39;t get any of them to stay together unless one member was significantly more massive than the others. They probably have a black hole too.
You are touching on a fairly recent controversy regarding the force of gravity. Astrophysicists have been doing the same modeling based on the observed speeds of the stars in neighboring galaxies, and they too have found that the stars on the outskirts of the galaxy move too fast to be held in their orbits if the only mass was in the form of the visible stars, gas, and dust. This is where the Dark Matter theories come from&#33; Based on the motions of those stars, and more easily on the motions of individual galaxies in a galaxy cluster, they can model what the distribution of mass should be to explain the motions and they have found that there should be vast clouds of matter, matter that they can&#39;t see through their telescopes, that surround and encompass the galaxy, or the cluster, to explain the motion of its constituents. A competing theory feels that gravitation, and our equations for motion, which all work well on smaller scales, need to be modified when dealing with the more massive objects in the universe.

Also, and interestingly tied to your comments, is that the central SMBH&#39;s size is directly corelated to the speed at which the outermost stars in a galaxy orbit. They still have no idea why this is, but like you said, the SMBH seems to be important in holding the galaxy together.

John
2004-May-10, 04:39 PM
Originally posted by StarLab@May 10 2004, 04:20 PM
So how can a BH have such a strong grip, yet it only sucks in what&#39;s nearest to it? If the galaxy lasted a bit longer, would the sun eventually be pulled into the middle, waiting in line for its ticket to the BH?
You have to remeber a few details about gravity and a quirk related to SMBH. For small black holes the change in the intensity of the gravitational field as you approach the black hole is gradual, but with a super-massive black hole the change in intensity is fairly sudden and close to the event horizon. This means that an object can with some safety orbit a SMBH at close range without experiencing extreme tidal effects.

And gravitation has no limit to its range and propagates at the speed of light. An like light eminating from a source, the intensity of the gravitational field decrease quickly as you move away from it, but it is never zero. Therefore, objects close in can get drawn in because they lack the necessary escape velocity to escape the curvature of space induced by the mass of the SMBH, while objects at the edge of the galaxy can simply maintain secure and safe orbits about the center mass of the galaxy without ever falling inward. Only perturbations to the outer objects&#39; orbits, such as our star passing too close to another massive object and having our orbital path or speed change to move us into the interior of the galaxy, would cause a star like our star to fall into the center of the galazy and possibel into the central SMBH itself.

tony873004
2004-May-10, 06:42 PM
Originally posted by John@May 10 2004, 04:39 PM
You have to remeber a few details about gravity and a quirk related to SMBH. For small black holes the change in the intensity of the gravitational field as you approach the black hole is gradual, but with a super-massive black hole the change in intensity is fairly sudden and close to the event horizon. This means that an object can with some safety orbit a SMBH at close range without experiencing extreme tidal effects.
I don&#39;t quite understand this. Shouldn&#39;t both small black holes and SMBHs have their gravity diminish as an inverse^2? Or is it just that a small black hole has a smaller event horizon so therefore you can get closer where the tidal effects are strong?

Also, this term everyone is using about a black hole sucking stuff in is misleading. It sucks stuff in like Earth sucks in meteors. In both cases, the sucked object has to be on a collision course to begin with.

John
2004-May-10, 07:15 PM
Originally posted by tony873004+May 10 2004, 06:42 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (tony873004 @ May 10 2004, 06:42 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-John@May 10 2004, 04:39 PM
You have to remeber a few details about gravity and a quirk related to SMBH. For small black holes the change in the intensity of the gravitational field as you approach the black hole is gradual, but with a super-massive black hole the change in intensity is fairly sudden and close to the event horizon. This means that an object can with some safety orbit a SMBH at close range without experiencing extreme tidal effects.
I don&#39;t quite understand this. Shouldn&#39;t both small black holes and SMBHs have their gravity diminish as an inverse^2? Or is it just that a small black hole has a smaller event horizon so therefore you can get closer where the tidal effects are strong?

Also, this term everyone is using about a black hole sucking stuff in is misleading. It sucks stuff in like Earth sucks in meteors. In both cases, the sucked object has to be on a collision course to begin with. [/b][/quote]
It is the size of the event horizon.

Sphinx
2004-May-11, 03:37 AM
correct me if I&#39;m wrong but isn&#39;t the event horizon asymptotic? Wouldn&#39;t this account for the difference in gravitational pull of the event horizon between the 2 different sized BHs? A larger black would steep much quicker than a smaller black hole. I may be way off base here.

Another question: why don&#39;t they send a huge camera with all kinds of sensors on it into a blackwhole? Wouldn&#39;t this provide a lot of very usable data?

zephyr46
2004-May-11, 05:03 AM
http://www.aoc.nrao.edu/~gcnews/gcnews/Recent/03orbit_pr.jpg

Orbits of stars near SagA* (http://www.aoc.nrao.edu/~gcnews/gcnews/Recent/gcnews.shtml) (GC newsletter (http://www.aoc.nrao.edu/~gcnews/gcnews/Recent/gcnews.shtml))

Antoniseb (http://www.universetoday.com/forum/index.php?showtopic=3026) posted a thread about a possible micro-lensing event in 2018.

I found the article interesting because it mentioned so many different types of black hole.

Kerr black Holes
the Schwarzschild black Hole
Reissner-Nordstrom black holes



as well as SMBH, it talks about Spherically Symetric black holes.

Very interesting, I am still crawling through the physics of it though :blink:


Does anyone know of any closer Black Holes or candidates than V4641 (http://homepage.ntlworld.com/brian.kilby/astro/2000/jan/closest.html)?
http://antwrp.gsfc.nasa.gov/apod/image/0001/v4641_vla.gif
APOD (http://antwrp.gsfc.nasa.gov/apod/ap000117.html)

John
2004-May-11, 01:31 PM
Originally posted by Sphinx@May 11 2004, 03:37 AM
Another question: why don&#39;t they send a huge camera with all kinds of sensors on it into a blackwhole? Wouldn&#39;t this provide a lot of very usable data?
There are two problems with this:

The first is that there are no black holes in our solar system. One of the nearest know (at least expected) is Cygnus X-1, and it is lightyears away. We have nothing now that could get a probe that far without it running out of power before reaching the black hole.

The second is that nothing, not even light, can escape from a black hole once it has reached or passed the event horizon, and all the stuff we don&#39;t really know about and want to learn is inside the event horizon. Radio, laser, microwaves, or any other known form of long range communication is all just photons of light, and since they can&#39;t escape the black hole we would never know what the probe saw. Even as the probe got close into the black hole, the relativistic effects of the intense gravity field would redshift the signal out of the ability to detect it anymore, unless you planned for that and had detector of multiple wavelengths ready to pick up the redshifting signal. And even then the event horizon would promptly terminate the signal and end the mission.

Guest
2004-May-12, 01:19 PM
BLACK HOLES DON&#39;T DIE&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;

JESMKS
2004-May-12, 04:02 PM
If light can&#39;t escape from a black hole, does that mean the acceleration of gravity at the event horizon is equal to the speed of light? If so, wouldn&#39;t an object passing through the event horizon accelerate to a speed greater than the speed of light?

John
2004-May-12, 04:39 PM
Originally posted by JESMKS@May 12 2004, 04:02 PM
If light can&#39;t escape from a black hole, does that mean the acceleration of gravity at the event horizon is equal to the speed of light? If so, wouldn&#39;t an object passing through the event horizon accelerate to a speed greater than the speed of light?
Insightful question&#33; The answer to the first question is Yes. The acceleration due to gravity at the event horizon is equal to the speed of light. That is why they say that nothing, not even light, can escape a blak hole once the event horizon has been crossed.

And the second question is the part that no one can answer. There are several reasons why they say that the known laws of the universe seem to completely break down inside of a black hole. One of those is that if the acceleration due to gravity is the speed of light at the event horizon, then it should be more idside, but that violates the law that nothing can go faster than light. There are other issues with infinite curvature of space inside and infinite density at the singularity, too. These are some of the reasons that they know our current understanding of the universe is incomplete.

Guest
2004-May-12, 10:44 PM
If light can&#39;t escape from a black hole, does that mean the acceleration of gravity at the event horizon is equal to the speed of light? If so, wouldn&#39;t an object passing through the event horizon accelerate to a speed greater than the speed of light?
I cannot answer your second query because is is pure speculation.
But for query 1, John is wrong in the following way: does the acceleration at EH equal the velocity of light? No. Why? because velocity and acceleration are dimensionally inequal (I have not yet taken a physics class - how neat that I know this crap&#33; :lol: ;)) meaning that the units m/s does not equal m/s^2, which is obvious. So any velocity cannot equal an acceleration. They are two different physical quantities.

John
2004-May-13, 03:50 PM
Originally posted by Guest+May 12 2004, 10:44 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Guest &#064; May 12 2004, 10:44 PM)</td></tr><tr><td id='QUOTE'>But for query 1, John is wrong in the following way: does the acceleration at EH equal the velocity of light? No. Why? because velocity and acceleration are dimensionally inequal (I have not yet taken a physics class - how neat that I know this crap&#33; :lol: ;)) meaning that the units m/s does not equal m/s^2, which is obvious. So any velocity cannot equal an acceleration. They are two different physical quantities.[/b]
I disagree. At the event horizon the acceleration caused by the gravitation of the black hole is equal to the speed of light. Any object trying to escape from this point would therefore have to travel faster than the speed of light to escape. The event horizon is the point of no return because nothing can travel faster than light&#33;

To put it another way, if gravity is accelerating you in one direction, in order to remain motionless relative to that object you need to apply an equal and constatnt acceleration in the oposite direction, counteracting the gravitational attraction. The other option is to travel at a speed perpedicular to the object in order to maintain an orbit. Any object that cannot exceed that gravitational attraction, or maintain a sufficient speed perpendicular will be drawn into it, and at the event horizon that speed does equal the speed of light.

<!--QuoteBegin-From Wikipedia
According to Schwarzschild&#39;s solution, a gravitating object will collapse into a black hole if its radius is smaller than a characteristic distance, known as the Schwarzschild radius. Below this radius, spacetime is so strongly curved that any light ray emitted in this region, regardless of the direction in which it is emitted, will travel towards the center of the system. Because relativity forbids anything from travelling faster than light, anything below the Schwarzschild radius including the constituent particles of the gravitating object will collapse into the center. A gravitational singularity, a region of theoretically infinite density, forms at this point. Because not even light can escape from within the Schwarzschild radius, a classical black hole would truly appear black.

The Schwarzschild radius is given by:

http://en.wikipedia.org/math/e085e1367479bea1b15234d34fef8c06.png

where G is the gravitational constant, M is the mass of the object, and c is the speed of light. For an object with the mass of the Earth, the Schwarzschild radius is a mere 9 millimeters.[/quote]

Sphinx
2004-May-14, 02:08 AM
ahhh.....if light can&#39;t escape from the center then we arn&#39;t seeing the center. We&#39;re seeing an absence of light, hence, black hole. The object may still be there but not that we can see because its light isn&#39;t going to be traveling in our direction or in any direction.

Do black wholes have a front or a back? Come to think of it...I don&#39;t think I really know what one looks like. I&#39;ve always pictured some huge eye shaped distortion of space with a rippled ring of distorted mass at the center with a deep dark black whole in the center. I also picture depth being very evident from a side view. This, of course, is probably more of my creativity than reality.

TheThorn
2004-May-14, 03:30 AM
Originally posted by John+May 13 2004, 03:50 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (John @ May 13 2004, 03:50 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-Guest@May 12 2004, 10:44 PM
But for query 1, John is wrong in the following way: does the acceleration at EH equal the velocity of light? No. Why? because velocity and acceleration are dimensionally inequal (I have not yet taken a physics class - how neat that I know this crap&#33; :lol: ;)) meaning that the units m/s does not equal m/s^2, which is obvious. So any velocity cannot equal an acceleration. They are two different physical quantities.
I disagree. At the event horizon the acceleration caused by the gravitation of the black hole is equal to the speed of light. Any object trying to escape from this point would therefore have to travel faster than the speed of light to escape. The event horizon is the point of no return because nothing can travel faster than light&#33;

To put it another way, if gravity is accelerating you in one direction, in order to remain motionless relative to that object you need to apply an equal and constatnt acceleration in the oposite direction, counteracting the gravitational attraction. The other option is to travel at a speed perpedicular to the object in order to maintain an orbit. Any object that cannot exceed that gravitational attraction, or maintain a sufficient speed perpendicular will be drawn into it, and at the event horizon that speed does equal the speed of light.

[/b][/quote]
I think you know what you mean, John, but the way you are expressing it is wrong. Like the Guest said, acceleration and velocity cannot be equal, because the units are different - acceleration is the rate of change of velocity.

What you mean, (and what you said in other parts of your post) is that at the event horizon, the escape velocity (not the acceleration due to gravity) is equal to c. There is a difference.

Interestingly, a photon that is moving tangentally to the event horizon will be bent into a circle around the black hole. It will essentially orbit the black hole at the event horizon. One that is moving directly away from the singularity can&#39;t slow down (it&#39;s light, after all, and will always travel at c), but it will be red shifted to 0 frequency by the gravity as it tries to escape. Poof, it&#39;s gone.

Greg
2004-May-16, 07:44 AM
Everyone should thank super massive black holes for forming galaxies. And that includes our own. So in every way imagineable our lives as we know it would not be possible were it not for their existence. I am surprised, given the implications that some fringe group hasnt started worshiping them, but given time that will probably happen too.
Like anything else in the universe its always easier to understand what exists now by understanding what existed before. For hundreds of millions of years after the big bang the universe was too hot for atoms to form. Eventually it expanded and cooled enough for hydrogen to precipitate and form. This took place everywhere. For reasons unknown it did not take long for the hydrogen to begin to clump into the first stars. These stars were truly colossal giants, hundreds and even thousands of times bigger than our sun. Such stars had short lives, however and quickly went supernova forming large black holes. The first generation of black holes then merged and gathered more hydrogen. The bigger the black hole got the more hydrogen dust from the interstellar medium it would attract.
So black holes are essential to galaxy formation, and every galaxy probably has one at its center. The bigger the black hole the galaxy has the bigger t he galaxy is (and the faster things rotate around it.) The smaller the black hole the smaller the galaxy and the more likely it is to be pushed around and broken up by another galaxy. Since ours is the biggest for hundreds of millions of light years, we are safe from being ejected into the intergalactic void by an unfortunate encounter with a larger galaxy. That could change when we collide with Andromeda, but that is billions of years from now.

StarLab
2004-May-16, 06:19 PM
Still, it might take longer for humans to find their way out of the galaxy than it would for Andromeda and our galaxy to collide. :ph34r: We should be thankful, but let&#39;s save it for when the resulting galaxy collision dies down. At least then we&#39;d know we weren&#39;t unfortunately wiped out...

Guest_John
2004-May-17, 04:44 PM
Greg,

The CMB appeared 380,000 years after the Big Bang when the universe cooled enough for neutral atoms to form. Not million of years.

The Andromeda Galaxy is larger than the Milky Way. It will collide with our galaxy in about 2,000,000,000 years. Although collision is probably the wrong word. They will gravitationally interact exchange mass and scattering some into intergalactic space. The odds of anything bad happening to our solar system is very slim.

StarLab,

I think we&#39;ll figure that out rather quickly. If we can find a shortcut through the universe, it will not only mean traveling to other stars quickly, but to other galaxies as well.

Greg
2004-May-18, 03:35 AM
Ok, well I was close. I could have guessed 10s of millions of years for hydrogen to appear. And Yes the "collision" with Andromeda will be more of a merger than anything. Since we are not within the outer arms of our galaxy it is very unlikely that our arm will be peeled away into space (like tendrils we see emanating from other colliding galaxies) when we approach Andromeda. There is so much empty space within our galaxy that another galaxy could theoretically pass right through it without a single star colliding or solar system interacting. The same does not go for the dust clouds, however. They will ne profoundly effected resulting in a burst of big hot young blue stars.

John L
2004-May-18, 02:39 PM
Greg,

You&#39;re right, and its that star burst that would be the most dangerous to us. Image a few blue giants bathing the Earth in intense ultraviolet radiation from close proximity. That would be a tan no sunscreen could block.