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Oliver Morton

The Music of Science

The scale of the universe is amazing – but more astonishing still is the science that lets us understand it

Oliver Morton | January/February 2016

In the far reaches of the sky there are sun-bright discs as wide as solar systems, their hearts run through by spears of radiation that outshine galaxies. The energies that feed these quasars beggar all metaphor, and their quantification seems all but meaningless. What does it serve to know that they are converting matter to energy at a rate that equates to the complete annihilation of a planet the size of the Earth ten times a second? Or that all the fires of the sun, from its birth to its death, would be a few weeks’ worth of work to one of them? No human sense can be made from so inhuman a scale. Boggle, and move on.

Or stop, and appreciate that for all their grandeur, quasars are actually rather hard to see. Not one of them is close enough for the naked eye to pick out; even through the largest telescopes their mighty discs are but points of light. Again, the numbers are incomprehensibly enormous: billions of light years, when the longest trip taken by humans, to the Moon and back, is just a few light seconds. Yet here is a human connection that makes something wonderful of the spectacle. The billion-year journeys of the quasars’ light end at human telescopes. And there this far-flung light is not merely absorbed, but also understood.

In the 1960s the growing sophistication of radio astronomy made it possible to distinguish these particular dots from the millions of others in the night sky. They were found to be emitting far more radiation than stars did, and to be far more distant. Astrophysicists concluded that the quasars were powered by black holes, previously near-mythical objects created when matter becomes so densely packed that it wraps the fabric of space and time around itself, vanishing from the observable universe and leaving only its remarkably powerful gravitational field behind.

This was not just a stunning feat of the collective imagination. It was also a very quick one. In 1960 no one had knowingly observed a quasar in any wavelength whatsoever. By 1969 hundreds were known, and a detailed theory of black holes had been developed which accounted for the quasars’ remarkable properties. Matter pulled towards a large black hole is heated to extraordinary brightness by friction; from the swirling disc thus formed a constant stream of matter passes into the hole’s oblate “ergosphere” whence some is squirted out with even greater energy in jets that protrude from the quasar’s poles.

That men and women can, in a few short years, take tiny smidges of data from often ill-behaved instruments around the world and judiciously combine them with a wide range of physical theory – including the demanding mathematical subtleties of general relativity – to form an account of something not only unimagined but unimaginable to anyone without the new mental equipment this joint endeavour provided: that seems to me a source of wonder greater than the vastest of astronomical numbers.

The story did not end there. Astrophysicists elaborated on their early theories in various ways, sparking the odd spat or two along the way. Observers lengthened the range at which quasars could be spotted, allowing them to be used to probe ever earlier phases of the universe’s history. At the same time they added to the total tally, at first with alacrity, then as a matter of routine. About 200,000 are now known — as many quasars as there were known stars back in the 1960s. Most of them have been discovered by a robotic survey telescope at Apache Point in New Mexico with little by way of direct human intervention.

Perhaps most remarkably, quasars became useful. The Global Positioning System on which the world relies for everything from aircraft navigation to trips to the supermarket requires a precisely defined reference frame against which to understand the movements of the satellites that send out its signals and the planet that they orbit. Quasars provide this reference frame. Because they are so distant, their position on the sky is utterly constant. Because they are easily seen with radio waves, observations made all over the world can be combined in ways that specify those positions with great accuracy. The current International Celestial Reference Frame uses 3,000 quasars to define the axes against which all other measurements – of the Earth’s position, of satellites, and of everything else – are made. Thanks to quasars, these axes are specified with a precision of ten microarcseconds. That is the angle between a line connecting your eye to a point on the surface of the Moon and a second line connecting it to a point two centimetres to the right of the first. Only a map built on the farthest things in the universe can offer this sort of precision.

Every spatial measurement that relies on GPS now depends on the accuracy of our knowledge of the positions of quasars. The most powerful things in the universe have become a hidden but necessary part of the way we run modern life, unacknowledged but routine. These everyday guarantors of accuracy have been understood, demystified and put to work. Does that mean the wonder is gone?

No. It means that the wonder, like the quasar, is part and parcel of the human world. Which is where it always belonged.

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