By Meenambika Menon
What is a Black Hole? How is it formed?
A Black Hole is a region of space which is of immense gravity that nothing—not even light—can escape from it. Black holes form at the end of some stars’ lives, stars that are many times the mass of our sun. The energy that held the star together disappears and it collapses in on itself producing a magnificent explosion. All that material left over from the explosion falls into an infinitely small point. Large black holes can have tens to millions of times the mass of our sun trapped in a point smaller than the tip of a pin!
How is seeing a Black Hole made possible? What makes the recent developments special?
The Event Horizon Telescope (EHT) operates a planet-scale array of eight ground-based radio telescopes that are linked together. The EHT observations use a technique called very-long-baseline interferometry (VLBI) which synchronises telescope facilities around the world and exploits the rotation of our planet to form one huge, earth-size telescope observing at a wavelength of 1.3mm. VLBI allows the EHT to achieve an angular resolution of 20 micro-arcseconds, enough to read a newspaper in New York from a sidewalk cafe in Berlin.
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The latest development confirmed that if immersed in a bright region, like a disc of glowing gas, we expect a Black Hole to create a dark region similar to a shadow — something predicted by Einstein’s general relativity that we’ve never seen before. The theory of general relativity predicts that the heated material will illuminate the extremely warped space-time, making a dark shadow visible. This makes a confident ground for the scientists about the interpretation of their observations, including their estimation of the Black Hole’s mass.
Now we can finally ‘see’ the black holes, and investigate the extreme warping of space-time they are causing in a unique way. These results mark an important milestone for our understanding of the fundamental processes that determine the formation and evolution of galaxies.
What’s inside a Black Hole?
A Black Hole is defined as a region of space-time from which extremely strong gravity prevents anything, including light, from escaping. We know that matter falling into black holes is no different from the matter which can be found lurking around the rest of the Universe.
Why is it black?
It is called “black” because it absorbs all the light that hits it, reflecting nothing, just like a perfect black body in thermodynamics.
What is a singularity?
In the centre of a Black Hole is a gravitational singularity, a one-dimensional point which contains a huge mass in an infinitely small space, where density and gravity become infinite and space-time curves infinitely, and where the laws of physics as we know them cease to operate.
Current theory suggests that, as an object falls into a Black Hole and approaches the singularity at the centre, it will become stretched out or “spaghettified” due to the increasing differential in gravitational attraction on different parts of it, before presumably losing dimensionality completely and disappearing irrevocably into the singularity.
What is an event horizon?
A one-way boundary in space time surrounding a Black Hole. In general relativity, an event horizon is a region in space-time beyond which events cannot affect an outside observer. In layman’s terms, it is defined as the shell of “points of no return”, i.e., the boundary at which the gravitational pull of a massive object becomes so great as to make escape impossible.
What happens when a spacecraft approaches a black hole? What is spaghettification?
As our spacecraft approaches it, the gravity will be so much stronger on the side closer to the black hole than at the other side that it will get completely stretched out like a piece of spaghetti. Essentially, when a particle draws too close to the source of the powerful gravitational field, it is stretched into long thin shapes, like pasta. The term was coined by Stephen Hawking in his book, A Brief History of Time, where he likened this process to spaghetti.
Any other fun facts on black holes?
- Black holes are only dangerous if you get too close.
- The nearest Black Hole is likely not 1,600 light-years away i.e 1.52 X 1012 Km approximately
- There are at least three types of black holes, NASA says:
(i) Primordial black holes are the smallest kinds, and range in size from one atom’s size to a
(ii) Stellar black holes, the most common type, are up to 20 times more massive than our own Sun.
(iii) Gargantuan ones in the centres of galaxies, called “supermassive black holes” each more than
one million times more massive than the Sun.
- There are so many films and movies using black holes, for example, that it’s impossible to list them all. Interstellar‘s journeys through the universe includes a close-up look at a Black Hole.
(Inputs: spaceplace.nasa.gov; physicsoftheuniverse.com; scitechdaily.com)
(The writer is Lead, Curriculum – Science & Math at Shiv Nadar School.)