That Gurjot

Witness the normal

Blackholes, Grapes and Silver Surfer

06 Feb 2013

“I am a Physics major you see, I just had to write about something to do with the Universe.”

Why Black Holes then?

“Black Holes have a mystery to them and are probably the most interesting things in the Universe. We know so much about them, yet so little. Just like infinity; you can attribute so much to them, but in the end, there’s not much you can say for sure. A friend shared a Vsauce video a few days ago. That’s what gave me the idea of writing about black holes.”

How do you know about all this?

“I just finished a course, “Intro to Astronomy” on Coursera. So most of it comes from there. The video I mentioned was quite helpful in streamlining my thoughts. Then there was the Internet. I did some research, like I always do, and I think I am ready to go about it now. Won’t keep it scientific much, promise.”

Well, the stage is all yours..

(insert dramatic science music here)

BLACK HOLES

When a star runs out of energy and is too massive to be stabilized by neutron degeneracy it starts to reduce in volume and grows so small in size that a stage is reached where its density becomes so high and its gravitational attraction so large that it becomes a region in spacetime which prevents anything, including light from escaping. Thus, aptly named - a Black hole. Mathematically, anything can become a black hole, if only it could be compressed to a certain parameter called the Schwarzchild Radius. Compress an object to that size and voilà, we have a black hole.

“O Great One! How do we calculate this amazing radius?” We use a thing called gravitational red shift. Leaving out the Newtoning as promised, we come down to this:

Where is our Schwarzchild radius, G the Universal gravitational constant, c the speed of light in vacuum and M is the mass of the body in question.

Go on! Calculate your Schwarzchild radius! Oh, ain’t good at math? Or not in a mood for some Newtoning? Just type “2* G *M/c^2” in Google Search and you should have your answer. Don’t forget to plug in the value of M! in kg of course, SI system always.

Now comes the fun. An average human has a Schwarzchild radius of the order of 10^-25 metres. How small is that you might wonder? Allow me to devise a new unit, a nanofemtometer. That is very, very small. Just take my word for it. Here’s a parallel. 1 femtometer is equal to 10^-15 m; atomic nuclei have a size of that order.

What if the Earth were to become a black hole? What would its Schwarzchild radius be? Here’s a picture of 14 Earth black holes:
1 inch! For Earth to become a black hole you would have to compress its entire mass into a volume of radius 1 inch!

“Whoa… Sensei, if a black hole is.. black? How do we see it in space?”

Bear with me for a while as I speak some science. Whenever there’s a massive body in the field of light, it bends its path. Since a black hole is as dense as anything could get, it bends the light so much so that all we see is a smudge. So if I were to look at the Leaning Tower of Pisa with a black hole blocking the view, the Tower would appear to circle around the dark center, everything would be fuzzy though. Putting this thought into the Universal picture now, imagine a galaxy far far away. Any light that that galaxy emits will appear to circle around the black hole in between. So this is how we see the black holes in space.

The purple ring around the center is the light from the distant galaxy.

“Alright. Good enough. But wouldn’t a black hole just suck up the entire universe?”

Ha, no. Thank God (sparking another debate with this) for that. There’s another parameter called Event Horizon. In general relativity it is a boundary in spacetime beyond which events can not affect an outside observer. For a black hole any object within this boundary is good as dead.* So event horizon is like the Lakshmana Rekha for the rest of the Universe.

EXCEPT SILVER SURFER! In Galactus the Devourer, Silver Surfer did actually escape from a black hole!

Just for shits and giggles, let’s see what would happen if an object or maybe insert your favourite enemy were to fall into a black hole. How would it look like to an observer? And more importantly, how would it feel like?

OK. So if a body starts falling towards a black hole, it would appear to go slower and slower as it approaches the event horizon. Why slow, we’ll answer in a minute. When it reaches the event horizon it would seem like it is just stuck there. The inward descent ceases. After a (long) while the body would appear to be redder and then slowly.. just fade away and disappear into the oblivion. Sci-fi orgasms may commence. Now, why does it look like that? Gravity not only warps light, it also warps time! The image of the object that we saw at any given time was not from that instant but from a while ago. So when the body seems to be stuck it is actually already beyond the event horizon. The reddening of the image is because of the aforementioned interesting phenomenon called gravitational red shift.

The most important question of it all, what does it feel like? We can only guess. It is believed that the entire mass of the black hole is concentrated to one single point (an ambiguous term in its own sense). How big the hole surrounding it would be depends on the its gravitational pull; but to know exactly what happens in there would require a first hand experience, since light, sound, Speedy Gonzales, Road Runner and not even Usain Bolt can escape from a b hole. So unless you are Silver Surfer, don’t wander too far. Just for fun let’s throw Usain Bolt in there. As he falls deeper inside his body would get stretched, and not just stretched, it’ll get spaghettified as Stephen Hawking calls it in A Brief History of Time. Aaaand, you are dead already. Here’s the fun bit. Light gets stuck inside, right? An assumption is that the light photons start revolving around the singularity (the point mass) and so you can actually see the back of your head! Photons reflected from your head will revolve all over the hole and go into your eyes. Crazy? I know! Another possibility could be that.. science fiction alert the inside of a black hole is actually a Worm Hole, letting you go from one universe to another or just letting you traverse within the same universe instantly! Such worm holes have been known to exist in:

  • Pokemon Blue (Team Rocket’s building?)
  • Age of Mythology (That God power, comes in Act III I guess.. or maybe the underworld.. I can’t recall)
  • X - Men (Nightcrawler)
  • Silver Surfer!

Fun facts about Blackholes

  1. They are mind numbingly dense. No not like the junkie at the curb, physically dense. Allow me to demonstrate using the Earth as an example.
    Mass of Earth =
    Schwarzchild radius of Earth =
    Density =
    which works out to be of the order of 10^30 kg/m^3!

  2. They are the best power plants, ever. According to Hawking radiation, particle-antiparticle radiation is emitted from just beyond the event horizon. This radiation does not come directly from the black hole itself, but rather is a result of virtual particles being “boosted” by the black hole’s gravitation into becoming real particles. Energy generated is about 10^50 times your average nuclear fusion!

  3. They have got varieties. There are spinning b holes, electrical b holes and according to the mass there’s miniature, stellar and super massive black holes. But that’s like comparing Pepsi to Coke, you can not escape any of them. Regular black holes swallow mass, while spinning black holes merge black holes together and can spin so fast they can actually act as particle accelerators. There’s this one guy spinning at over 1000 times per second.

  4. We all come from Black holes. Quoting Carl Sagan’s the sentence - “The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of star stuff.”

Sources:

Here’s a test video: