Falling into a black hole: Just what do you see?

Everyone loves black holes. Immense gravity, a one-way space-time membrane, the possibility of links to other universes. All lovely stuff.

A little trawl of the internets reveals an awful lot of web pages discussing black holes, and discussions about spaghettification, firewalls, lost information, and many other things. Actually, a lot of the stuff out there on the web is nonsense, hand-waving, partly informed guesswork. And one of the questions that gets asked is "What would you see looking out into the universe?"

Some (incorrectly) say that you would never cross the event horizon, a significant mis-understanding of the coordinates of relativity. Other (incorrectly) conclude from this that you actually see the entire future history of the universe play out in front of your eyes.

What we have to remember, of course, is that relativity is a mathematical theory, and instead of hand waving, we can use mathematics to work out what we will see. And that's what I did.

I won't go through the details here, but it is based upon correctly calculating redshifts in relativity and conservation laws embodied in Killing vectors. But the result is an equation, an equation that looks like this

Here,  rs is the radius from which you start to fall, re is the radius at which the photon was emitted, and ro is the radius at which you receive the photon. On the left-hand-side is the ratio of the frequencies of the photon at the time of observation compared to emission. If this is bigger than one, then the photon is observed to have more energy than emitted, and the photon is blueshifted. If it is less than one, then it has less energy, and the photon is redshifted. Oh, and m is the mass of the black hole.

One can throw this lovely equation into python and plot it up. What do you get.

So, falling from a radius of 2.1m, we get
And falling from 3m
And from 5m
And 10m
and finally at 50m

In each of these, each line is a photon starting from different differences.

The key conclusion is that within the event horizon (r=2m) photons are generally seen to be redshifted, irrespective of where you start falling from. In fact in the last moment before you meet your ultimate end in the central singularity, the energy of the observed photon goes to zero and the outside universe is infinitely reshifted and vanishes from view.

How cool is that?


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    What's inside a black hole

    What's inside a black hole Black holes are mysterious and bizarre objects in the universe that really have no explanation. In fact We hardly know anything about what lies inside of a black? Hole we know and understand what we see on the outside of a black hole But we have no way of going inside one to take a look at what is really happening Even if we sent a probe inside a black hole It would not survive the journey And there would be no way that the probe could transmit a signal outside once it had been sucked inside This is because a black Hole is the product of mass being squeezed together, so densely and so tightly that it creates a gravitational pole That is so strong that not even light can escape its grasp Supermassive black holes with masses millions to billions of times that of the Sun are thought to lurk at the hearts of all galaxies in the universe You may notice that when you see a photo of a spiral galaxy Such as the Milky Way in the center of the galaxy is a giant mass of light? Which many people would think looks like a massive Sun, but this is not light coming from the black hole itself Remember that life cannot escape the heavy gravitational pull Instead the light we see comes from magnetic fields near a spinning black hole that propel electrons outward in a jet Along the rotation axis the electrons produce bright radio waves Quasars are believed to produce their energy from massive black holes in the center of the galaxies in which the quasars are located But quasars are so bright they drown out the light from all the other stars in the same galaxy. You're probably asking: Well What's a quasar? A quasar is the short name for a quasi stellar object and is a very highly energetic object. Surrounding an actively feeding supermassive black hole in more basic terms the supermassive black hole in the middle of a galaxy feeds intermittently as it feeds gas swirls around it at incredible speeds and Forms an insanely bright hot orbiting disc and if the black hole is swallowing a large amount of material this feeding is accomplished by gigantic Jets of gas these are called quasar They are essentially fueled by the black holes They orbit some supermassive black hole giants release an extraordinarily Large amount of light when they rip apart stars in devour matter and are likely the driving force behind these quasars When material gets too close to a black hole it forms that bright hot accretion disk around the black hole That accretion disk heats up to millions of degrees Blasting out an enormous amount of radiation The magnetic environment around the black hole forms twin Jets of material which flow out into space for millions of light years This becomes what is called an active galactic nucleus Or a GN the diet of known black holes consists mostly of gas and dust which fill the otherwise empty space throughout the universe black holes can also consume material torn from nearby stars in fact the most massive black holes can swallow stars whole Black holes can also grow by colliding and merging with other black holes This growth process is what can and usually does reveal the presence of a black hole? Read More Yt

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