BLACK HOLES

Minutes of GD on Black Holes

• Brought to attention because of the recent success in photographing a black hole
• Facts

1)Every galaxy has a black hole that holds it together due to strong gravitational pull

2)Light can’t escape black hole because its escape velocity is more than ‘c’. This follows from the notion that light has a dual nature and tends to behave like matter upon interaction, therefore, getting sucked in the black hole despite 0 rest mass of the photon

Analogy-

Black hole = whirlpool and light = boat around the whirlpool

3) It’s said that light travels in straight lines but if the space itself is bent then light also bends in the absolute sense and since, the valley of black hole is so deep, light doesn’t come back from it. Also observed experimentally in the General Relativity Theory which is based on the astronomical phenomenon – the solar eclipse- stating, theoretically that the stars beyond the sun shouldn’t be visible but practically it was observed that they were visible because light bent around the sun

4) Chandrashekhar limit = 1.4x (mass of sun)

If mass of a star 3-4 times the mass of sun, it has the           potential to form black hole

5) Minkowski space – When you go near an object, time span wrt that object increases

7) The team which reconstructed the photo was led by Kathy bowmen .

X-ray expulsion from this spread 5000 light years away and this was used to triangulate the exact place. This X-ray image was processed to be a colour photo

• Formation-

Process of fusion converts mass to energy. In this process when stars collide, the mass decreases, subsequently leading to a reaction which prevents it from expanding, thus, contracting to extremely small size (highly dense -large mass, less volume) via space-time collapse

          Trampoline analogy-

If mass is put on a trampoline, a ‘space-time fabric’, it collapses to form a black hole

• LIGO experiment

1. To detect gravitational waves ( formed when mass bursts into pieces, causing energetic explosion like ripples)
2. MSU alumni, 1 of the contributors
3. 2 L-shapes pipes were put perpendicular to each other (1 km X 1 km) and a common source of light was used to observe interference

(because of 0 phase difference)

1. Due to gravitational waves, space-time contracts, causing phase difference and thus not yielding the expected result
2. 2 LIGOs work in conjugation

• Applications of black hole related info

1. It is one of the openings of the concept of a worm hole (the other being white hole and connected via a channel – space thread), which is theoretically perceived to be like a portal to connect to different places

In order to enter the worm hole, theoretically, a negative mass is needed to create repulsion because positive mass will exert gravitational force, breaking the space thread

Negative mass concept is purely theoretical because it implies negative energy, which can only be achieved when the said body keeps radiating more and more energy spontaneously to attain larger negative value

1. Helps us understand space and time more accurately, facilitating in inter planetary travels

• If forward space is contracted and backward space is expanded, speed of light is achieved
• If there’s relative velocity between 2 objects, time is either fast or slow for Object A wrt to Object B
• You’ll never see objects going inside black hole
• Theoretically, the person inside the black hole’ d perceive the outside world to be really fast

• Spaghettification

The gravitational force eqn of black hole is

dF/dx = very large

=> The gravitational pull of the black hole would be much stronger at the part touching the surface of the black hole compared to a part further away

 Therefore, if a person goes near a black hole, he’ll be stretched like a spaghetti before getting his body broken down into pieces

• There’s a minimum black hole size which makes it conducive for entry
• To observe the black hole, telescopes, the size of earth were needed but due to non-feasibility of the idea, it was decided that 8 different telescopes’d be put up in different parts of the world, linked with quantum clocks,, the data from all of them collected and from all the infinite possibilities, the most probable ones were singled out and were pieces together to give a complete picture using a complicated algorithm

Multiple images were multiplexed and error patching was done

Image with least noise was ideally the most likely one

5 petabytes of information was processed and transported from all the observatories to a specific location via planes, due to huge bulk of info

• NASA has been observing a specific star for a couple years to finally get this picture
• This pic substantiates Einstein’s hypothesis that he formulated sitting on his desk

• To determine how far the light is coming from amount of red shift is used
• Some of the musing during the GD

1. During solar system formation, more than 9 celestial bodies existed (8 planets + Pluto) but most of them collided with each other and got destroyed while the others had sufficient radial velocity from sun and sufficient velocity to rotate around the sun
2. Philosophy leads to scientific discoveries

• Fe is the most viable element because it has the largest Binding energy per nucleon value
• Pre – mordial Black hole formed intially due to non-homogeneity of masses
• Large Hadron Collider

Huge radial tunnel in Switzerland, France of 12 km radius is used to accelerate positrons at large velocities and then collided with each other, during which for a very brief period, space-time collapses, creating small black holes. This is why several physicists are against it

• Black hole information paradox

Black hole destroys all the information when the info enters it and this lost info collects on the surface of the black hole like a hologram and since all the light eventually goes there, all the information across the galaxy is archived there (like Cooper’s experience in Interstellar)

• The Big Bang theory explains post explosion phenomena because it had the potential to develop a black hole but due to large outward force, there was outward expansion of the he infinitesimal energy packed in the highly dense, small, ball of energy.

Since, BBT fails at explaining what happened before, religion tries to fill in the gap

Very specific conditions ensured that the universe gets created which opens up to the possibility of more such places in what is known as the ‘Multiverse theory’

• To explain why the image looks the way it does, one could imagine that if the black hole was positioned in the x-z plane, then the photo was clicked from the x-y plane

Minutes by

SHIVANSH (1st year )