Black Hole census.

[alokmohan]

NASA scientists using the Swift satellite have conducted the first complete census of galaxies with active, central black holes, a project that scanned the entire sky several times over a nine-month period. <br /><br />The all-sky survey contains more than 200 supermassive black holes called Active Galactic Nuclei, or AGN, and provides a definitive census of black hole activity in the local universe. The team uncovered many new black holes <br />

 

[qso1]

Quite a development. It wasn't that long ago that black holes were not known to exist at galactic centers. With billions of galaxies out there...lots of black holes. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[alokmohan]

But we know since long that galaxies have a supermassive hole in center.It is mere confirmation.But black hole census is funny idea.

 

[qso1]

True that black holes have been theorized to exist and more or less confirmed largely by data since AFAIK, a black hole has yet to be directly imaged and by their very nature may be impossible to image. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[alokmohan]

What is AFAIK?

 

[qso1]

As far as I know. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[alokmohan]

I add it to my vocabulary.Nice thing.

 

[MeteorWayne]

It is funny, especially when you have to make the follow up visits to those that don't return the survey cards <img src="/images/icons/tongue.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[alokmohan]

I add it to my vocabulary also.Actually I stay in India.So I LEARN.tEACH ME WHENEVER YOU GET A CHANCE.But dont teach me a good lesson.

 

[SpeedFreek]

Seeing as Hawking admitted he was wrong, maybe more black holes would return their survey cards than we previously thought! <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[alokmohan]

RemiNds me of unsung hero of black hole.John MItchel.He propounded dark star.It is such a star whose escape velocity is spted of light.First edition of black hole.This was exotic thing,but Mitchell never thought in way now we thinkIt much before theory of relativity came.Then we never discuss Laplace.We forget heros.

 

[alokmohan]

In 1785 John Michell,a British natural philosopher,dared to combine the corpuScular description of light with Newtons Gravitational laws and thereby predict what very compact stars should look like.He did this by a thought experiment. Launch the particle from surface of a star with some initial speed,and let it move freely upward.If the initial speed is too low,the stars gravity will slow the particle to a halt and then pull it back to the stars surface.If the initial speed is high enough,gravity will slow the particle to a halt and then pull it back to the stars surface.If the initial speed is high enogh,gravity will slow the particle but not stop it.the particle will manage to escape.The dividing line,the minimum initial speed for escape is called the escape veolocity.........Mitchel then calculated what should be critical circum ference for for which the escape velocity is the speed of light......Hr calculaed it have dia of 18 km and called it dark star,we call it black hole today.

 

[alokmohan]

Founder of black hole?

 

[alokmohan]

Mithells dark star caused no stir.It was simply made of things we knew,it was very dense only.It was of matter as we know it.It did not hurt any cherished beliefs.

 

[alokmohan]

John Mitchel propounded dark star.In 1783 he submitted paper to Royal society.

 

[alokmohan]

Concept reappearBy definition a black hole is a region where matter collapses to infinite density, and where, as a result, the curvature of spacetime is extreme. Moreover, the intense gravitational field of the black hole prevents any light or other electromagnetic radiation from escaping. But where lies the "point of no return" at which any matter or energy is doomed to disappear from the visible universe? <br /><br /><br /><br /><br />The Event Horizon<br />Applying the Einstein Field Equations to collapsing stars, German astrophysicist Kurt Schwarzschild deduced the critical radius for a given mass at which matter would collapse into an infinitely dense state known as a singularity. For a black hole whose mass equals 10 suns, this radius is about 30 kilometers or 19 miles, which translates into a critical circumference of 189 kilometers or 118 miles. <br />Schwarzschild Black Hole <br /> <br /><br /><br /><br /><br />If you envision the simplest three-dimensional geometry for a black hole, that is a sphere (known as a Schwarzschild black hole), the black hole's surface is known as the event horizon. Behind this horizon, the inward pull of gravity is overwhelming and no information about the black hole's interior can escape to the outer universe. <br /><br /><br />Apparent versus Event Horizon<br />As a doomed star reaches its critical circumference, an "apparent" event horizon forms suddenly. Why "apparent?" Because it separates light rays that are trapped inside a black hole from those that can move away from it. However, some light rays that are moving away at a given instant of time may find themselves trapped later if more matter or energy falls into the black hole, increasing its gravitational pull. The event horizon is traced out by "critical" light rays that will never escape or fall in. <br />Apparent versus Event Horizon<br /><br /><br /><br />Caption <br /><br />Even before the star meets its final doom, the event horizon forms at the center, balloons out and breaks through th

 

[nexius]

didnt stephen hawings revoke his statement about nothing being able to escape from a black hole?

 

[alokmohan]

I possibly saw it somewhere .Cant confirm right now.

 

[alokmohan]

Dont forget Mitchell ,Laplace,the founders of dark star.Dark star is now known as black hole.Named by Wheeler.