Blackholes for beginners
Black holes for beginners
This article covers all the basic knowledge you'll need to start learning about these giant, invisible voids lurking in space. From what blackholes are, to where they are found, this first part of the two-part article covers just that. Be sure to read my second blackhole post to learn some interesting facts about these dark stars.
It is the year 3021, and you are zipping through space in your new, high-tech, ultra-fast space ranger vehicle. You slow down to gaze at a bright, colourful cluster of stars in the distance, they seem to be moving, like waves back on Earth; a dazzling sight to the monotony of unending black space. However, the cluster zooms past in a shimmery blur, and you realise you have not slowed down at all, you are gaining speed. A force keeps pulling you and your vehicle, and you move faster and faster… Then suddenly, all is black, you have disappeared.
What are Blackholes?
While it is impossible for you to find yourself in this
situation, (unless humans discover how to travel at the speed of light) this is
the fate of any star which happens to get too close to a Black Hole. As the
name suggests, a Black Hole is essentially a black void in space, and gravity,
is one of its’ main principles. Strange as it seems, gravity here pulls so
hard, that not even light can escape it. A star that is adequately large and
compact would have such a strong gravitational field, that light cannot escape.
Any light that is given off from its’ surface, will be pulled back by the
stars’ gravitational attraction before it can get far.
How do Blackholes work?
Every planet and star have a critical value called the
escape velocity, which differs from one to the next. An object would have to be
travelling at this critical value, or at a velocity above it, to exit the
planets/stars atmosphere. For an object travelling at escape velocity, gravity
will not be strong enough, to pull it back to the surface, and so allowing the
object to “escape”, which it otherwise would not be able to do. The escape
velocity for Earth is 11.186 Km/s and the escape velocity of the sun is around
617.7 Km/s, for example. Now, a Black Holes’ escape velocity is so high, that
light, travelling at around 3 x 10^5 Km/s velocity, is not fast enough to
escape its’ atmosphere. Since no particle travels faster than the speed of
light, a blackhole acts as a large space vacuum cleaner, sucking everything
that gets too close, into it.
How are Blackholes formed?
But how are these, stranger than fiction, dark stars formed?
Blackholes start off as ordinary stars. Every star, large or small, has
hydrogen gas in and around their cores, and acts as a kind of fuel. Due to the
stars’ gravitational forces, the star begins to contract, the hydrogen gas is
constantly collapsing in on itself, and as a result, the hydrogen atoms
contract, causing them to collide with other hydrogen atoms, and generate heat
due to a higher rate of collision. Eventually the star becomes so hot that the
atoms do not bounce off each other after colliding, instead they merge or fuse
to form helium atoms. Heat is released in this process which makes the stars
shine so bright. This also causes an increase in pressure in the star, which
counters the gravitational attraction of the star, creating a balance. The star
no longer contracts, and stays stable like this until it begins to run out of
‘fuel’. Once the fuel is depleted past a mass limit (Chandrasekhar limit), the gravitational force of attraction becomes so large that the star collapses into a singularity, with infinite density, and virtually nothing can escape its' pull.
What are the different types of Blackholes?
There are primarily, 4 types of blackholes, and they are classified based on their size, the way they are formed and their location. Stellar mass blackholes, are the most commonly found and are around 10-20 times bigger than our sun. They are formed when a star dies and collapses on itself, this sometimes creates a supernova (the stars' outer layers burst out into space). If there's enough mass left after the star goes supernova, gravity can cause it to collapse on itself more, crushing it together into a point of infinite density, and so, forming a blackhole. Supermassive blackholes (SMBHs) have the mass of more than 1,000,000 suns (1,000,000 solar masses*), and exist at the center of galaxies based on evidence so far. Some even have masses 21 billion times than the mass of our sun (21 billion solar masses). Their large size and position in a galaxy is strongly suggested be related to galaxy formation; from the collapse of massive clouds of gas during the early stages of galaxy formation. Quasars are kinds of SMBHs, that continuously suck in matter, which emit bright radiation, allowing them to be seen easily. SMBHs are also the largest of all the black holes types. Intermediate blackholes have masses between those of stellar mass and supermassive blackholes. They can be formed when the oldest stars in the universe collapse, or when stars or other blackholes collide. These only exist in theory, as a single blackhole is theorized to suck really large amounts of matter, to reach the mass required to merge with another blackhole. Miniature blackholes are extremely small, some are even the size of an atomic particle, but with astonishingly high masses, around the same mass as Mount Everest! They are theorized to have formed just after the Big Bang, making them around 13.8 billion years old!
Blackholes near us :
The closest blackhole to Earth (as of June 2021) is 1500 light years from us, and has been given the title, 'The Unicorn'. It is three times bigger than the sun - one of the smallest to be discovered so far - a 'tiny' void, that was only recently discovered (April 2021). There's a SMBH at the center of the Milky Way too, it's called the Galactic Center (rotational center of the galaxy) with a mass of around 4.1 million solar masses, and is 25,800 light years away from the Earth. Blackhole A0620-00, 3500 light years away, Cygnus X-1, 6000 light years away and V404 Cygni, 7800 light years away are some of the nearest blackholes to the Earth.
Regions in Blackholes :
There are 5 main regions in blackholes that contribute to its' structure. The singularity, at the center of a blackhole, with infinite density, is the region where all sucked matter ends up. The whole mass of a blackhole is concentrated here. The Event Horizon, the region beyond which no object can escape the immense gravitational pull of the blackhole. Next comes the Photon sphere, which is the outer edge where light bends, but can still escape. The next region, the Accretion disk, is where extremely hot gas and dust whirl around the blackhole at incredible speed, radiating electromagnetic radiation, which can be used to spot the location of the blackhole. The last main parts of a blackhole are Relativistic jets. When matter is sucked into the Blackhole, jets of particles and radiation are emitted from its' poles at a little less than the speed of light, and these jets can extend for 1000s of light years through space.
* Solar mass - 1 solar mass is defined to be the mass of our sun, around 2^30 kg.
Find my second blackhole post here: https://cupcakesandrainbows123.blogspot.com/2021/06/more-about-blackholes.html
References :
- Brief answers to the big questions – Stephen Hawking
- The Theory of everything – Stephen Hawking
- Galaxies – kids discover
- Nasa.gov
- Encyclopaedia of world wonders
- Earthhow.com
- https://www.youtube.com/watch?v=e9TLbZuvsko
- NOVA PBS official - four types of blackholes
- ulzair aman khan slideshare
- scitechdaily.com
- www.newscientist.com
- astronomy.com/news
This is extremely insightful, especially for beginners like me. It has peaked my interest in learning more about this particular science! Good job Mani!!
ReplyDeleteThankyou so much, glad you enjoyed it Curry!
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