Stephen Hawking's new way of perceiving black holes !

gwenyi · Post by **gwenyi** » Sat Jul 17, 2004 4:28 pm

http://story.news.yahoo.com/news?tmpl=s ... ck_holes_4

Sam Lee · Post by **Sam Lee** » Sat Jul 17, 2004 4:50 pm

Wonder what findings would he present....

Regards,
Sam

ChaosKnight · Post by **ChaosKnight** » Sat Jul 17, 2004 10:01 pm

Speaking of black holes, can anyone answer this question?

Black holes are supposed to form when a supermassive star collapses.

Now, imagine there are two stars, A and B. Star A has the capability to form a massive black hole, while B just barely manages to form one.

We can imagine a core in A which is as massive as B.

Now, as A collapses, its core will collapse first to form a black hole. At a particular instant, there is a black hole similar to B. What we have is a black hole as massive as B, with material from the outer layers of A falling into it.

Except to observers outside, the material takes an infinity of time to fall through the event horizon. To us, a blackhole more massive than B is impossible to form.

Or put another way, blackholes do not really form, but are always on the verge of forming.

If this is so, how can we observe massive blackholes?
And all it takes is a little negative energy to destroy the blackhole should it form.

QuantumGravity · Post by **QuantumGravity** » Sat Jul 17, 2004 10:08 pm

I don't really understand your question... The "story" is rather confusing...

Anyway, you said that "Except to observers outside, the material takes an infinity of time to fall through the event horizon". I read from somewhere that the observers are the ones who will see the material taking infinite amount of time to fall through the event horizon. However, if the material will experience time as normal.

gwenyi · Post by **gwenyi** » Sat Jul 17, 2004 10:39 pm

ChaosKnight wrote:Speaking of black holes, can anyone answer this question?

Or put another way, blackholes do not really form, but are always on the verge of forming.

If this is so, how can we observe massive blackholes?
And all it takes is a little negative energy to destroy the blackhole should it form.

Well, to observe blackholes, we shouldn't be using the visible light spectrum to see them. Instead, we should be looking at the x-ray and gamma ray spectrums to assist us in doing so. That's why ,we are using spectrometers to detect the different electromagnetic waves in space.

One may ask, why are x rays given off ? In simple, the blackhole will suck material from its nearby stars into an acceretion disk. So when the material enters the black hole and hits a solid surface, the material glows even more brightly in high energy x-rays. Since there are heck lots of material being sucked in by the blackhole at any one time, the x rays given off can be credited to the smashing of the materials from the stars.

From what i believe, blackholes are constantly growing in their size. Everytime they gobble up more material from nearby stars, they grow in size. Black holes are formed in a fraction of a second after the life of a massive star(solar mass > 2.2) ends. The immense gravitational force of the star causes the core to collpase inwards to form a singularity.

So in a nut shell, black holes are formed in a fraction of a second after the star collapses, but are constantly increasing in their sizes.

cheers,
wenyi

Extraterrestrial · Post by **Extraterrestrial** » Sat Jul 17, 2004 11:32 pm

Even straitstimes reported it today. Blackholes aside, this guy studies the problem for 30 years. Admirable.

Post by **zong** » Sat Jul 17, 2004 11:58 pm

ChaosKnight wrote:Speaking of black holes, can anyone answer this question?

Black holes are supposed to form when a supermassive star collapses.

Now, imagine there are two stars, A and B. Star A has the capability to form a massive black hole, while B just barely manages to form one.

We can imagine a core in A which is as massive as B.

Now, as A collapses, its core will collapse first to form a black hole. At a particular instant, there is a black hole similar to B. What we have is a black hole as massive as B, with material from the outer layers of A falling into it.

Except to observers outside, the material takes an infinity of time to fall through the event horizon. To us, a blackhole more massive than B is impossible to form.

Or put another way, blackholes do not really form, but are always on the verge of forming.

If this is so, how can we observe massive blackholes?
And all it takes is a little negative energy to destroy the blackhole should it form.

With reference to the bolded line up there, to us observers outside, the material just falls in an vanishes from our view, although it will take some time to do so. If you were to see a black hole in the making, you would first see the supernova, and some time later matter starts falling in. You won't see those matter move, but instead, just fade from view. You would then know that they have fallen in. So they don't take infinity to fall in.

From the viewpoint of the material, time is as usual. It does not take forever to fall in, but if the material could feel, it would feel itself ripped apart into atoms, and eventually into quarks and leptons, and eventually smaller than that, and so on.

Observing massive blackholes take either the gamma or x-ray spectrum, or the use of "einstein's cross". In the "Einstein's cross" method, light from a star behind the black hole is bent by the black hole, so we would see many copies of the same star near the black hole. x-ray method was explained above. Gamma method detects Hawking radiation coming from the black holes. To learn more about it you can try reading up, because it takes just too long to explain about it...

gwenyi · Post by **gwenyi** » Sun Jul 18, 2004 12:04 am

just for reference, einstein's cross is also known as gravitational lensing.

cheers,
wenyi

QuantumGravity · Post by **QuantumGravity** » Sun Jul 18, 2004 1:05 pm

There's a question my school's astronomy team has been wondering about... why does the Einstein's cross has 4 copies and not more or less?

Post by **zong** » Sun Jul 18, 2004 6:22 pm

It's gotta do with the way the star is positioned behind the black hole with reference to our position. Any nearer or further or left/right or up/down, it might not be 4 copies already.