Black Holes

Better than sci-fi any day. (Vol. 2; Issue 46)

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The Stop

Formed at the death of a massive star, black holes are cosmic bodies of ‘extremely intense gravity from which nothing, not even light, can escape.’ The idea of such bodies was first suggested in the eighteenth century by the English natural philosopher John Michell,¹ though it wasn’t until 1915 when the German physicist Karl Schwarzschild - only one month after Einstein published the Theory of Relativity - was able to prove their mathematical probability. For decades considered a mathematical curiosity, it wasn’t until 1971 that they were proven to exist with the discovery of the first black hole, Cygnus X-1.²

Direct image of a supermassive black hole at the core of Messier 87.

A black hole is formed when a massive star - defined as a star larger than eight solar masses during its main sequence lifetime³ - exhausts the internal nuclear fuel in its core as it nears the end of its life. Up to this point in the life of the star, nuclear fusion has created a constant outward push in balance against the constant inward gravitational pull of the star’s own mass. However, as the fuel depletes, the core grows unstable and can no longer produce the energy required to keep gravity from causing the mass of the star to collapse violently upon itself.

The collapse of the star triggers a supernova explosion which blows its outer layers away into space, leaving the stellar core behind. If the crushed core contains more than about five times the Sun’s mass,⁴ ‘no known force’ can stop it from continuing to collapse and compress into itself until it reaches a ‘point of zero volume and infinite density called the singularity.’ Infinitely small and infinitely dense, the singularity contains all of the mass of the original star along with all the other matter that has been sucked in, though ‘crushed out of normal existence.’ A place physics knows exists but struggles to explain, the singularity is where the gravitational field becomes so powerful that the velocity required for matter to escape its pull exceeds the speed of light. Consequently, not even light can escape into space.

Astronomers estimate that around 100 million of these so-called stellar-mass black holes exist within our own galaxy, and for many years it was believed these were the largest objects of their kind. However, in the early 1990s it was discovered that the centre of nearly all large galaxies - including our own Milky Way - contains what scientists call a ‘supermassive black hole.’⁵ Having a mass of over one million Suns, the scale of these black holes and their corresponding gravitational pull is enormous. While black holes cannot be seen, the material around them is visible and appears as a disc - like a ‘whirlpool in a bathtub drain.’ The gravitational pull heats this matter as it moves around the black hole, causing it to emit detectable radiation. Consequently, by observing this material astronomers were able to notice a primary difference between stellar-mass and supermassive black holes: around the former the matter is composed of gas, but around a supermassive black hole at the heart of a galaxy, this disc is made up ‘not only of gas but also of stars.’

The Detour

Today’s detour is different as it’s to a webpage rather than video. However, visiting The Scale of the Universe is well worth the time and interaction; I’ve used it in class to try to impress upon students the relative sizes of things – and they’ve always enjoyed it. Starting with the size of an average human (1.7 metres/5.6 feet), scrolling left moves microscopically and right goes macroscopically - and clicking on any of the pictures provides a brief explanation and size. At the very least, it’s a unique perspective to think that we kind of exist on a razor’s edge between infinite space. Give it a try and let me know what you think.⁶

The Scale of the Universe

The Recommendation

Today’s recommendation is Stephen Hawking’s A Brief History of Time: From the Big Bang to Black Holes.⁷ An introduction to cosmology for the general reader, the book addresses such fundamental questions as ‘How did the universe come to be?’ and ‘Will it come to an end.’ Though not always the easiest read, technical jargon and mathematical knowledge are kept to a minimum as Hawking explains how the ideas of gravity, relativity, black holes have developed over the twentieth century. A must-read if you’re interested in any of this sort of stuff.

From the back: A landmark volume in science writing by one of the great minds of our time, Stephen Hawking’s book explores such profound questions as: How did the universe begin - and what made its start possible? Does time always flow forward? Is the universe unending - or are there boundaries? Are there other dimensions in space? What will happen when it all ends?

Told in language we all can understand, A Brief History of Time plunges into the exotic realms of black holes and quarks, of antimatter and ‘arrows of time,’ of the big bang and a bigger God - where the possibilities are wondrous and unexpected. With exciting images and profound imagination, Stephen Hawking brings us closer to the ultimate secrets at the very heart of creation.

You can buy A Brief History of Time from Amazon, of course, but you can also get it at your local new or used bookstore - or check it out from the library. And those options are better for everyone.

The Sounds

Though I originally began thinking thematically for this one, I changed my mind (Muse’s ‘Supermassive Black Hole’ appears on an earlier list) and decided to just choose five tracks tenuously connected in my mind to each other: ‘Lotus Flower’ (Radiohead, 2011), ‘Madness’ (Muse, 2012), ‘Inhaler’ (Foals, 2013), ‘Lonely Soul’ (UNKLE and Richard Ashcroft, 1998) and ‘A Letter to Elise’ (The Cure, 1992). Enjoy!

The Thought

Today’s Thought is from Stephen Hawking:⁸

‘One of the basic rules of the universe is that nothing is perfect. Perfection simply doesn’t exist …. Without imperfection, neither you nor I would exist.’

If you have a thought on this Thought - or any part of today’s issue - please leave a comment below:

And that’s the end of this Stop - I hope you enjoyed the diversion!

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Until the next Stop …

1. Michell - who’s also considered the father of seismology - announced this idea in 1783. In addition to being a geologist and astronomer, he was also a clergyman. For more information, see John Michell.

2. This is a big topic and so today’s issue is a very, very brief introduction to these most mysterious objects. Sources for today’s Stop include: Black Hole (Britannica), Black Holes (NASA), Black Holes (National Geographic) and Cox, Brian and Andrew Cohen. Wonders of the Universe. London: Harper Collins, 2011.

3. The mass of our Sun is the standard, so a massive star is roughly eight times the size of our nearest star.

4. Our Sun is not massive enough to become a black hole so, in five billion years when it runs out of the available nuclear fuel in its core, it will become a white dwarf. For more information on white dwarf stars, see: White Dwarf Star (Britannica).

5. Our galaxy’s supermassive black hole is known as Sagittarius A*.

6. Though I’d put the volume on silent as the wavering-spacetime-dream-music gets old rather quickly.

7. I was originally going to recommend Disney’s The Black Hole (1979). But, despite an at times (slightly) clever story and a few (ok) special effects, it’s actually quite rubbish. However, for the purpose of nostalgia, it is streaming on Disney+. Just saying.

8. For more information about Hawking, see: Stephen Hawking (Britannica)