Death of a Black Hole

This is a very Frequently asked question...

How do black holes die?

Well, some people think they last forever, and they're very nearly right. Black holes do die, but it is on a timescale of billions of years. No one has ever seen a black hole actually die, but astrophysics Stephen Hawking has proposed a theory about black hole death.

Black holes aren't black at all. In fact, they constantly emit radiation in the form of small virtual particles that are born in pairs out of photons, i.e. particles and antiparticles. At the event horizon, there is a sort of gravity well, which seperates the innards of the black hole from the outside. At this point, the energy is sufficient enough for the photons, or energy packet (also called quanta) to 'condense' into matter. Since the law of conservation of mass and energy is maintained, the particles have to be each others' anti selves.

Mostly, these particles do not last more than a few millionths of a second, quickly annihilating each other to form photons again. This is the actual Hawking radiation, the emission of photons by such a physical reaction. Unfortunately, this radiation is much too faint to be detected by even the most powerful telescope on earth.

But sometimes, it doesn't work out so well for the particle. They do not get to meet with their other halves. The anti particle gets whisked away beyond the event horizon, falling down the intense gravity into the object's core. The other particle is left partner less, and wanders off alone. Since it has a positive mass, it has a positive momentum and it can escape the gravitational field of the black hole (mind you, the event horizon is the point of no return. Anything outside that can and will escape).

The antiparticle goes and annihilates with a positive particle at the black hole's core, thereby reducing the mass of the black hole by one particle.

So what happens then?

Billions of years later, the mass of the black hole drops sufficiently to fall beneath the Chandrasekhar limit of 1.44 Solar Masses. At this stage, Pauli's exclusion principle kicks in. The particles, that have been oppressed and crushed into this tiny little space for billions of years by their own gravity, explode outwards violently. The energy released in this explosion is phenomenal. It could blow away half of the galaxy in which the black hole resides. Let's just say that if the Black hole at the centre of a galaxy a few billion light years away exploded by this method, when the light eventually reached us, it would make our nights as bright as day. That is the awesome power of an exploding black hole.

Will we be able to see one any time soon?

No. Like I said, black holes don't live forever, but they come very very close. If the theory is correct (and so far, it has never been disproved, and all evidence seems to back it), it'll be a few billion years (few hundred billion years, actually) before one does die. And even then, depending on its distance from us, it'll take even longer for the light to reach us. But, as you know, Earth isn't gonna last more than 5 billion more years, thanks to our daddy, the Sun. It's gonna become an old star, expand its size till it engulfs all four terrestrial planets (Mercury, Venus, Earth and Mars) before shrinking into a tiny white dwarf that will eventually cool off to become a hunk of helium floating in space.

More on this cheerful topic of the Earth getting fried next time... Tune in to Young-Geniuses.

Big Bang continued...

Another reason why the Big Bang is a plausible theory is according to the CMB radiation observed by Arno Penzias and Robert Wilson in 1964, for which they rightfully deserved the Nobel Prize in 1978.

With a traditional optical telescope, the space between stars and galaxies (the background) is completely dark. But a sufficiently sensitive radio telescope shows a faint background glow, almost exactly the same in all directions, that is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. At first, Penzias and Wilson thought it was an error, and even cleaned up the telescope of pigeon droppings. But then, when the glow persisted, they realised that it had to come from the Universe itself, and was almost exactly the same on all sides.

What is CMB radiation?

CMB radiation stands for Cosmic Microwave Background radiation. It is the after glow of the Big Bang, the residual energy that was released during the moment of creation.

But how is this related to the Big Bang?

The Universe is vast, far greater than what we can observe with even the most sensitive, powerful telescopes. The CMB radiation observed is almost equal from all sides. That means that the residual energy is more or less evenly spread out all over. But since nothing can travel faster than light, that means heat can't either. This implies that if the Universe was always this big, then the heat wouldn't have enough time to radiate in all directions equally, leading to HUGE holes in the detected radiation.But it is all even. That means that at some point of time in the past, the Universe was relatively close together, close enough for the heat to flow even to all points.We know the state of the Universe today, and we can calculate the distance the Universe must have had to have the heat flow evenly. Joining these two 'points', we can say with enough evidence that at some point of time, or the zero time, as physicists refer to it, the Universe was compressed into a zero space (not exactly zero, but the nearest possible). This then exploded, or expanded, or inflated, whichever you prefer, into the Universe we know today.

That, my dear friends, is the Big Bang.

Big Bang of Physics

Welcome to the Big Bang of Physics.

This is Mangesh Sonawane, and I'm here to introduce to you, in small ways, the huge and extremely interesting world of Physics. Of course, many of you know much about what I'm going to tell, but this is largely devoted to those who do not know much.

What is Physics?

Physics is the branch of science that deals with the physical realm of our Universe. The 'how' of things is associated with physics, and by extension, all the 'what','where','when' and 'why'.

I'm gonna start of with the basics of the Universe, and then move on to the Big Stuff.

What is this physical Universe?

The physical Universe is what we can observe in a very tangible way. What we can see, touch, tast, hear, feel and sense, all come under physics, or at least, analysis of the phenomena does. It includes everything from the largest stars to the smallest particle. From spacetime to th cosmic foam, everything comes under the physical Universe.

Let's start with the birth of the Universe.

How was the Universe born?

The most convincing and widely established theory is that of the Big Bang. So how did this theory come by?

Combining his own measurements of galaxy distances based on Henrietta Swan Leavitt's period-luminosity relationship for Cepheids with Vesto Slipher's measurements of the redshifts associated with the galaxies, Hubble and Milton L. Humason discovered a rough proportionality of the objects' distances with their redshifts. He discovered that with the increase in the distance, the redshift also increases. This led them to formulate the empirical Redshift Distance Law of galaxies, nowadays termed simply Hubble's law.

Redshift is a phenomenaon that is associated with the Doppler effect with light. As the distance between two points increases, the light becomes increasingly redder. This is because the expansion of space expands the wavelength as well.

If all stars and galaxies are moving away from each other, than means at some point of time they were all close together. Even further back, the Universe might have been cramped into a space smaller than an atom. At such a high density, all laws of Physics might have broken down. So anything that came before the Big Bang need not be considered.

Of course, the above explanation fits well with Euclidean space, which has three physical dimensions and one of time. But physicsits don't really like this theory, because it includes singularities, and physicists hate singularities because all laws of physics break down here. But the string theory has another view of space and time; that of Imaginary space. It is not imaginary in the general sense, but in the mathematical sense.