“Like there are infinite possibilities out there and I could be part of any one of them”: Dr Becky Smethurst’s ‘Space | 10 Things You Should Know’
“When I look at the majesty of the night sky, with the Milky Way stretching out overhead in a huge arc of stars, I don’t feel anxious. I feel limitless. Like there are infinite possibilities out there and I could be part of any one of them.”
This was absolutely superlative from one of my new favourite storytellers.
The 10 titular things (or voorwerpjes, to reference Hanny van Arkel’s quasar light ionisation echoes, i.e. “thingies”): why gravity matters, in the beginning there was nothing, a brief history of black holes, just because you haven’t seen it yet doesn’t mean it doesn’t exist, how far we’ll go, in pursuit of Earth 2.0, why the night sky is dark, aliens probably exist, the original chicken or the egg, and we don’t know more than we do know.
A few favourite facts…
Earth’s 23 degree tilt, the reason for the seasons, was caused eons ago by a mighty collision with a proto-planet in the early days of the solar system that liquefied half of the original Earth, which was then flung out into space and pulled into a spinning disc by the remaining Earth’s gravity that then later clumped together to form the Moon.
By studying the motions of the stars at the centre of the galaxy for decades we discovered that at the very heart of the Milky Way, in a region of space that could fit inside Mercury’s orbit, there is a supermassive black hole four million times the mass of the Sun. The work of Hawking and others then showed that black holes can be described with the same language as thermodynamics — they radiate energy with the temperature proportional to the surface gravity. In 1978 another scientist called Sergeant studied Messier 87 more closely, the largest elliptical galaxy known, and how fast the central stars were moving, deducing that they orbit something a billion times the mass of the Sun…
Through the 1980s these titans had been referred to varyingly as Massive Dark Objects and, by theorists, as black holes, with a debate also about whether they were a single object or a swarm… Measurements and calculations continued, with the Andromeda galaxy’s centre observed to be 10 million times the mass of the Sun and the Sombrero galaxy another billion. Then with the launch of the Hubble telescope radio interferometry (radio telescopes separated by hundreds of miles that combine into one super telescope) proved these were all single bodies. The Hubble showed Messier 87 indeed had this object of a billion solar masses but that it was only 0.25 arc seconds across – an arc second being the Babylonian measurement for a subdivision of one degree, each split into 60 minutes, each minute into 60 seconds – far too small for a cluster of stuff… In 1995 Makoto Miyoshi also used radio interferometers to show that in Messier 106 there was a compact object 10 million times the mass of the Sun in 1.3 parsecs (0.42 lightyears or 26,000 astronomical units) – again too much mass in too small an area. Supermassive black holes were the only answer… Finally there was consensus that all galaxies are powered by accreting black holes, any visual variance just depends on the angle we see them at due to the accretion being a very thin disc (e.g. you might see it as a blazar, a quasar, or a radio galaxy).
The first image of a black hole was taken in 2019 by the Event Horizon Telescope network of the behemoth beating at the heart of Messier 87, a galaxy hundreds of thousands of light years across with a giant jet of radio emission shooting out from its black hole for over 10 million light years.
“If Messier 87 was the size of a grain of sand, the supermassive black hole at its centre would be the size of an atom and the jets from it would extend across the entire palm of your hand.”
One of the reasons that black holes so perplexed and infuriated 20th-century astrophysicists after Einstein had published his theory of general relativity in 1913 was because, according to Schwarzschild’s equations that presented an exact solution to Einstein’s field equations describing the behaviour of a gravitational field outside a spherical mass, you’d eventually get to a point where space has been bent completely vertical, at least in two dimensions, with a huge mass in an infinitely small space i.e. if you increase mass enough gravity becomes infinite, which is messy maths, because it means you have to divide by zero… which means the limit does not exist…
It was none other than Edgar Allan Poe who was one of the first to refute Olbers’ paradox, the dark sky paradox i.e. the assumption that the universe is homogenous, the same in all directions, and infinite, which would mean “at every single light year step, in any direction we look, we’d have the same amount of brightness as a single star only a light year away. And with infinite number of light year steps the night sky would be blindingly bright” or in Poe’s words:
“The sky would present us a uniform luminosity, like that displayed by the Galaxy — since there could be absolutely no point, in all that background, at which would not exist a star. The only mode, therefore, in which, under such a state of affairs, we could comprehend the voids which our telescopes find in innumerable directions, would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all”.
The presence of Saturn in our very unusual solar system is the only reason why Jupiter has not gradually migrated closer to the Sun over the eons and slingshotted Earth entirely out of it.
Saturn, we salute you.
“When I look up at the sky and think about the sheer number of stars out there, I can’t help but get excited about drawing the conclusion that we can’t be the only planet whose cards came up right in the game of life.”
