Black Hole : General Information
Black Hole : General Information
Black Hole : General Information
∞Black Hole∞
General Information
Black holes are the strangest things in existence,they don’t seem to make any sense
at all.Black hole is a region of spacetime that exhibits such stong gravitational forces that not
even particles and electomagnetic radiation,meaning light,cannot escape. It is a great amount
of matter packed inside into a very small area,for example think of a star 10 times more massive
than our Sun squeezed into a sphere not bigger than the New York city.So,because no light can get
out,we can’t see them directly.Despite its invisible interior, the presence of a black hole can be
inferred through its interaction with other matter and with electromagnetic radiation such as
visible light. Matter that falls onto a black hole can form an external accretion disk heated by
friction, forming some of the brightests objects in the universe. If there are other stars
orbiting a black hole, their orbits can be used to determine the black hole's mass and location.
Such observations can be used to exclude possible alternatives such as neutron stars. In this
way, astronomers have identified numerous stellar black hole candidates in binary systems,
and established that the radio source known as Sagittarius A, at the core of the Milky Way.
galaxy, contains a supermassive black hole of about 4.3 million solar masses.As dangerous
this unknown objects seem they still remain the creators of us,without them galaxies weren’t
possible,without galaxies stars couldn’t exist,and finally without stars,planets and life
couldn’t form,so as we,humans on a tiny planet like other full of life and hope,Earth,cradle of
humanity.
Stars are incredibly massive collections of mostly hydrogen atoms that collapsed
from enourmous gas clouds under their own gravity,heat and pressure cause the hydrogen
atoms to violenly collide with each other,this collision further heat the gas until the
hydrogen atoms don’t collide,instead they form helium atoms.The mass of a helium atom
is less than 2 combined hydrogen atoms,so the remaining mass is released as energy,the
maginitude of which is given by einstein’s famous E=mc2(squared).The energy realeased
might be small for two coalescing atoms,but for billions and billions of them the
acumalative release is tremendous.In the core,nuclear fusion crushes hydrogen atoms into
Bunea Matei 26th of November 2018
♦ 1.2Growth
Once the black hole has formed,it will continue to absorb matter from it’s
surroundings,like interstellar dust.Another way of growing is merging with other stars or
black holes.They can eat almost everything,this is the only reason why super massive
black holes exist,especially in the center of evey galaxy,being the only explenation for the
forming of every galaxy,it’s the only celestial body that can keep and give shape to a
galaxy with the help of the greatest gravitational forces.
♦ 1.3Evaporation
really empty,but filled with virtual particles popping into existence and anihilating each
other again and again.When this happens right on the edge of a black hole,one of the
virtual particles will be drawn into the black hole,as we said nothing can escape the
gravitational pull at the event horizon,and the other particle will escape and become a real
particle,so the balck hole is losing energy,this happens incredebly slow at first,and gets
faster as the black hole becomes smaller,when it arrives at a mass as a large asteroid,it’s
radiating at room temperature(20 degrees),and when it reaches the mass of a mountain,for
example Everest,it’s radiating with about the heat of our Sun,at the surface(6000
degrees).In the last second of it’s life the black hole radiates away with the energy of
billion of nuclear bombs in a huge explosion,but this process is incredebly slow,the
biggest black hole we know estimated, it will take up to 10 to the power of 96 years to
evaporate.Stephen Hawking radiation equation shows that black holes can indeed radiate
energy and conserve entropy (disorder). According to the second law of thermodynamics
entropy implies heat and therefore temperature. Hawking’s calculations predict a black
body temperature of a couple nano-Kelvin; low indeed but an energy emission
nevertheless. This means that black holes do not exist infinitely, they rather evaporate.
2.Physical Properties
face the direction towards the black hole.Closer to the event horizion and beyond there is
no chance that any particle will escape,not even light.Thsi border completely separates
black holes from the rest of the universe,we can’t acces them unless we are willing to
never return.Now we do not really know what’s happening beyond this edge.With the
help of General Relativity,we know that massive objects distort the space and time
fabric,so if we imagine a trampoline and we drop a bowling ball on it,we can see how it
bends the material,now if we drop some rubber balls they will start to drift towards the
curvature and then orbiting the bowling ball.This example shows how gravity works and
there is a relation with time, as the distortion is steeper so as the time will be longer.And
depending on the position of an object on that curvature,the time and gravity will
change.Closer,the gravity is stronger and automaticly the time stretches more and further
it will be the opposite,shorter time,weak gravity.For an observer far away from the black
hole time will be slightly more faster than one observer near the black hole wich time will
pass extremely slow for him,know as gravitational dillation.
♦ 2.2Singularity
The singularity is the region of the black hole where all the material of the
remnants is gathered,it’s concentrated in an extremely small point that accoding to
General Relativity it curves spacetime so much that it becomes infinite.We are not sure
what it is exactly.For rotating black holes the singularity will look like a ring and for a
static black hole like a dot.A gravitational singularity may be infinitely dense,meaning
that the mass is concentrated in a space with no surface or volume,and the gravity too is
almost infinite at the center.Observers falling into a Schwarzschild black hole ( non-
rotating and not charged) cannot avoid being carried into the singularity, once they cross
the event horizon. They can prolong the experience by accelerating away to slow their
descent, but only up to a limit; after attaining a certain ideal velocity,When they reach the
singularity,they are crushed to infinite density,and their mass is added to the black
hole.Before that happens,they will have been torn apart by the growing tidal forces in a
process also called spaghettification,the gravitational force is so stong that a body is
pulled it will pass areas that have a difference of 1 meter for example,as we know
acceleration is rate velocity as time passes, so here but more extreme,a human would fell
stonger effects at the legs than at the head.Mathematically, a singularity is a condition
Bunea Matei 26th of November 2018
where equations do not provide valid values. Our current equations, based on general
relativity theory, are not sufficient to describe conditions of the singularity.
♦ 2.3Ergosphere
Ergosphere is a region outside the event horizon, where gravitational forces start to
influence objects movements. Objects here can no longer remain stationary in space.
Depending on the distance between object and to the event horizon, the influence can be
extremely strong or very weak. Close to the event horizon, where escape velocity is nearly the
speed of light gravitational will rip objects apart and eventually draw most of their material in.
Far away the effects are virtually non-existent. Objects in the Ergosphere can escape the forces
of a black hole if their speed is higher than the appropriate escape velocity.General relativity
theory predicts that any rotating mass drags surrounding space-time with it. This makes the
ergosphere not just a characteristic of black holes, but it is present with all regular cosmic
objects of mass, including earth, planets or the sun.Objects and radiation can escape normally
from the ergosphere. Through the Penrose process, objects can emerge from the ergosphere
with more energy than they entered. This energy is taken from the rotational energy of the
black hole causing the latter to slow.Rotating black holes are surrounded by a region of
spacetime in which it is impossible to stand still, called the ergosphere. This is the result of a
process known as frame dragging, general relativity predicts that any rotating mass will tend
to slightly "drag" along the spacetime immediately surrounding it. Any object near the rotating
mass will tend to start moving in the direction of rotation. For a rotating black hole, this effect
is so strong near the event horizon that an object would have to move faster than the speed of
light in the opposite direction to just stand still
Sources: ° https://en.wikipedia.org/wiki/Black_hole
° https://www.youtube.com/watch?v=e-P5IFTqB98
° https://www.youtube.com/watch?v=yWO-cvGETRQ&t=66s
Subject: Physics
Proffesor:Tugce Goktas
Name:Bunea Matei
Date:26th of November 2018