More about Blackholes

Read this article to find out some cool and wild theories about Blackholes!

What happens to objects as they fall into a blackhole?

As an object moves closer and closer to the blackhole, the gravitational pull on it becomes stronger, and in the case of a stellar blackhole, a process called spaghettification happens; the object in pulled and stretched into a string of subatomic particles due to the uneven forces of gravity acting on the further, and closer ends of the object.  The two ends of the object experience vastly different gravitational environments as gravity increases rapidly, closer to the blackhole. However, in the case of super-massive blackholes, the force of gravity is so intense that each end of the object experiences in equally, and hence will not be spaghettified as it crosses the event horizon, but, will blink out of existence at the singularity at the blackholes' core.  

Spaghettification visualization

If that isn't strange enough, things get even weirder! If a person happened to jump into a supermassive blackhole, and make it to the singularity alive, they'd be able to see everything around them, and outside the event horizon clearly, however, they won't be able to send signals out, as any form of waves or particles would be pulled back into the singularity with them. This ability to see everything outside the blackhole, from the singularity, actually only works one way. Someone observing you from outside the blackhole, will never see you entering it. Once you reach the event horizon, you'd just be, well... stuck. Then you'd seem to turn redder and redder, until you can't be seen anymore!

Computerized image of the inside of a supermassive blackhole

What is spacetime, and how does it work around a blackhole?

Spacetime is an idea which combines the 3 dimensions of space, and 1 dimension of time, into a 4 dimensional continuous extent throughout the universe. This is the fabric of the universe, which gravity can warp. Since blackholes have an infinite density at their singularities, their gravity is also infinite, and so, infinitely and severely warps spacetime. For this reason, time is experienced very differently near blackholes. For an outside observer, an object nearing a blackhole will gradually begin to slow down, before just stopping, as mentioned above. 

A blackhole warping spacetime

Another thing that would happen if a person were to remain alive at the singularity of the blackhole, is that they'd be able to see everything that has ever fallen into the blackhole, everything in it, and everything that is yet to enter. They'd most probably know all the secrets of the universe, the moment the universe was created, how the universe will(or perhaps has already) end(ed). They'd see the past, present and future all at once, since spacetime is so continuously warped, and time itself is said to end at the singularity. Pretty neat!

Due to the immense gravitational force, anything that goes near a blackhole is reduced to millions of subatomic particles, before they disappear into the seemingly endless blackhole. This leads us to more intense and un-wrap-your-head-around theories. 

What goes on inside the singularity, and where do the fallen objects go?

To be honest, no one really knows what happens at the singularity. Scientists believe that the fallen objects contribute to a rise in mass of the blackhole, causing its gravitational force to increase. Theoretically, this should be true, as objects that fall into the blackhole, have mass. The particles of the object may go into the singularity, adding to the increase in concentrated mass, or may accumulate on the outsides of it. Scientists have found out that not all particles of an object that fell into a blackhole, enter the singularity, but eventually escape the blackhole in the form of special waves. This happens to particles of the object which are repelled by the singularity. This blackbody radiation was first discovered by Stephen Hawking in the year 1973, so the idea of 'nothing can escape a blackholes' pull' isn't entirely true. 

This was called Hawking radiation, and is believed to be emitted because of quantum effects near the event horizon. Like other blackbodies, blackholes lose energy through the emission of these waves. For a long time, it was thought that the mass of a blackhole decreases when this happens (*), but recent studies of ripples created by the merger of two blackholes (detected using LIGO), show that the surface area of the merged blackhole is in fact larger than the sum of the areas of the two blackholes that merged, and so proves that the mass of the blackhole doesn't decrease over time. 

Two blackholes merging in 2016

Predictions about blackholes are made using mathematical equations, and it just so happens that something out of our wildest imaginations may be real: a parallel universe. 

Whiteholes and time travel

It's theorized that the singularity of a blackhole leads to the center of a whitehole. This behaves in an opposite manner to blackholes, in every aspect. While things fall into a blackhole, a whitehole shoots them out. Scientists think that this can be caused by the heavy distortion of the space time field, which causes an inverse in space. Most features of these whiteholes resemble the Big Bang (the moment in time when the universe was created). In 2006, a Big-Bang-like phenomenon was seen in a nearby galaxy; an extremely bright burst of light, and matter being created in 102 seconds (much longer than the Big Bang is predicted to have been). Whiteholes are only predicted to exist for a few seconds at a time, as, otherwise, it would be contrary to the second law of thermodynamics**, in which case, the body witnessed in 2006, might as well have been a whitehole in action! 

Depiction of the 2006 'mini big bang' phenomenon. GRP060614 ~ supposed whitehole

Scientists think that a blackhole and whitehole can act as a sort of 'portal' for time-travel. If time moves forward in our universe, then on the other side of the whitehole, time can move backwards, and since the two bodies are believed to be connected through a loop in spacetime, it may be possible to reach an alternate universe, as well as during a different time period! 

A tear in the spacetime field, connected at two ends, can possibly link two universes together and allow time travel, is called a wormhole. Wormholes also exist, only in theory, but are predicted to allow an object to travel far stretches of the universe in a very short amount of time, even faster than at the speed of light. A wormhole will essentially look spherical, like a blackhole, while the distant place would be visible through its' center. 

Graphic representation of a wormhole

 

* The law of conservation of mass/energy ~ Mass/Energy can neither be created nor destroyed

** Second law of thermodynamics - any spontaneously occurring process will always lead to an increase  in the entropy (S) of the universe. The entropy can never decrease. (entropy = disorder) Whiteholes 'create' new bodies, and so reduces entropy, hence, in a way, violating the law.

So these were 4 mind-boggling theories about blackholes, put in a simple way. I hope this encourages you to search up, and learn more about these fascinating outer-space bodies!

Read my first blackhole post here, to become more familiar with the idea :    https://cupcakesandrainbows123.blogspot.com/2021/05/blackholes-for-beginners.html

                                                                                                                              ~ ♡ Mridini

References :

- Theory of everything (Stephen Hawking)

- Brief answers to the big questions

- https://www.youtube.com/watch?v=XRW7mSCaD-M

- https://skyandtelescope.org/

- shutterstock

- https://www.indiatoday.in/science/story/black-hole-stephen-hawking-theory-einstein-ligo-physics-1818057-2021-06-22

- https://inventionsky.com/what-is-white-hole/

- https://www.bing.com/videos/search?q=wormholes+-+kurzgesagt&view=detail&mid=A565A6C75D26C34745E2A565A6C75D26C34745E2&FORM=VIRE

- Photo(wormhole) by Mark Garlick

- Harvard/smithsonian image of spaghettification

- Credit: NASA, ESA, and D. Coe, J. Anderson, and R. van der Marel (STScI)~ inside a supermassive blackhole

- Science Photo Library RF