Richard Easther
I chalked up a personal first yesterday; I saw an aurora with my own eyes and it was every bit as remarkable as I could have hoped for. I was not alone in sharing this special moment – anyone outside before midnight without clouds overhead in New Zealand (and, in fact, much of the world outside of the tropics) could have done the same, as these displays are driven by a once-in-decades solar storm.
Continue reading “Keep Looking Up”
Amongst everything else that happened in 2023, a key anniversary of a huge leap in our understanding of the Universe passed largely unnoticed – the centenary of the realisation that not only was our Sun one of many stars in the Milky Way galaxy but that our galaxy was one of many galaxies in the Universe.
Continue reading “A Bigger Sky”
New Zealand is suddenly and unexpectedly a “spacefaring nation”, with locally built rockets regularly launched to orbit and even the Moon. This is a shock to many – it certainly surprised me, and I live and breathe this stuff. But now that we find ourselves with an unexpected lead in a couple of key events in the Space Olympics, how do we make the most of it?
It’s always nice to wake up to good news, and it is not necessarily a common experience as we reach the end of the second year of a pandemic. But for astronomers, two decades of anxiety were laid to rest over the weekend as the last mirror segments of the James Webb Space Telescope, or JWST, were locked into place.
One of my earliest memories is standing with my father on the balcony of my grandmother’s house in Auckland. “Ma’s House” had a spectacular view northwards, across Auckland’s Hauraki Gulf, and the Moon was visible in the early evening sky. Following my eye, my father pointed and said, “I think there are people there at the moment.”
I would love to describe this as the father-son moment that lit my lifelong passion for astronomy, but doing so would take me far from the truth. My love of astronomy must have already been well aflame, because my actual recollection is that this was the first time I saw my father – a man frequently summoned to the hospital to tend the sick, who could fix any broken toy and who was able to split logs with an axe – as imperfect, fallible and human. How could any adult, I wondered, not know exactly how many people were standing on that pale little ball at any moment?
My memory is that this moment took place during a pre-Christmas visit. Looking at the list of Apollo missions I can work out the date: the only landing in any December was Apollo 17, the last mission, just after my sixth birthday in 1972. While it was clear that there would be hiatus in lunar travel after Apollo 17, it is still a shock to realise that I am now in my 50s and that no one significantly younger than me can have a clear memory of a moment when human beings were standing on another world. Ever since that day there have always been precisely zero people standing on the surface of the Moon.
The Apollo landings took place against alongside the Vietnam War and the Civil Rights struggle and constituted the winning entry in a race with the Soviet Union, a competition animated by superpower rivalry. But they are also a story of commitment, courage, teamwork and vision, a literal moonshot that shines as a moment of optimism and purpose. Perhaps even more so when you set it against the wider turmoil of the 1960s. I am not the first person to say this, but before Apollo “flying to the Moon” was a byword for an impossible, ridiculous dream – afterwards it was a metaphor for what can be done when we set ourselves to achieve lofty goals.
Sooner or later we will go back. Several countries and even SpaceX, a private company, are developing concrete plans to return human beings to the Moon. However, even with the most optimistic schedules those new voyages are still a few years off.
If it seems that we have had an unduly long wait, it is worth recalling that after the first trips to the South Pole — with sleds pulled by men and dogs — it was close to 50 years before human beings again stood at 90 degrees South but those subsequent visits were made with tractors and planes, and marked the beginning of a permanent human presence at the Pole.
Similarly, the Apollo missions pushed their 1960s technology to the absolute limit, and Apollo 13 escaped tragedy by the narrowest of margins. While the final missions spent several days on the lunar surface, the Apollo programme would have been hard-pressed to provide the foundation for a permanent lunar base. When humans do go back to the Moon, they will do so using spacecraft and rockets that have been developed to the point where lunar travel can conceivably become routine.
And then – perhaps in a decade or two — a permanent human presence on the Moon will develop to the point where even the best-informed parents might be forgiven for not knowing exactly how many people are standing on the Moon.
IMAGE: The header image is from the Apollo 16 mission. The launch photo above is Apollo 11, on its way to the moon atop a Saturn V rocket. Both images via NASA.
The analogy between lunar and polar exploration has been made by a number of people — I believe I first heard it from the (now sadly deceased) polymathic Columbia astronomer Arlin Crotts, when we were colleagues in the early 2000s, and it appears in his book The New Moon.
The media is full of stories about the impending release of the first ever images of a black hole – images that not only represent cutting edge science, but are the culmination of 200 years of speculation and theory moving ever closer to observation.
This is huge for astrophysics, and a stunning example of how the mundane rules of our tangible, everyday world give physicists the ability to make intellectual leaps into the unknown – and the long-thought unknowable.
The idea of a black hole can be traced to a calculation by English “natural philosopher” John Michell in 1783.
Along with his contemporaries, he imagined light as a stream of particles. Like balls thrown with superhuman force, these corpuscles emitted by the sun had no trouble reaching escape velocity and sailing away into space.
Michell pulled on a loose intellectual thread, asking how big a star would need to be before its own light could not escape its clutches.That is, when would the gravitational field of a star become so strong that, rather than setting off into the distance, light would fall back to the stellar surface?
Using no more than today’s high-school physics, Michell worked out that you could reach that point of no return by scaling up the sun by a factor of 500. A star 500 times greater in radius than the sun would be 125,000,000 (500x500x500) bigger by volume, and thus would “weigh” 125 million solar masses.
At that size, such a giant would become a dark star – vanishing from view.
Michell was working with the Newtonian model of gravity. In 1915, Einstein wove space, time and gravity into a single fabric with his General Theory of Relativity. Working in Berlin, at the heart of an empire locked in a global conflict, he hammered out a set of equations that explained gravity as the stretching of spacetime by massive objects. In the Einsteinian framework. the gravitational field of single, stationary object is described by the Schwarzschild metric, named for artillery officer Karl Schwarzschild, who did the maths while being treated for a painful (and eventually fatal) disease in a hospital near the Russian front, in the months after Einstein published his original equations.
To derive the Schwarzschild metric, you first imagine the object as a single idealised point. In the vicinity of this point, the math tells us that space and time turn inside out. This makes it impossible for light – or anything else – to escape past the event horizon into the world beyond. Beyond the event horizon normality is restored, and to the outside observer, it marks the external boundary of the black hole.
Mathematically, the black hole itself consists solely of empty space — it is a pucker in the fabric of spacetime. It is not so much that a black hole has mass; rather, the black hole is a memory of where mass once was.
The event horizons you would have calculated for all known astronomical objects in 1915 were far smaller than their actual size, in contrast to the vast dark stars extrapolated by Michell. In other words, after Einstein, black holes came to be understood as the endpoint of a collapse.
By the 1930s the pieces of what we now call “modern physics” – relativity, quantum mechanics, nuclear physics, along with a nascent understanding of particle physics – had been assembled. Armed with these tools, astrophysicists set about exploring the inner workings of stars. In the 1950s and 1960s we first observed pulsars and quasars (powered, respectively, by neutron stars and black holes) whose very existence is contingent upon these newly discovered laws of physics and these discoveries inspired that new field of “relativistic astrophysics”.
Texas became the epicentre of this emerging field – and two New Zealanders had ringside seats in the early 1960s. One of them, Beatrice Tinsley, went on to do fundamental work on the evolving universe; the other was mathematician, Roy Kerr, who took the step beyond Schwarzschild by solving Einstein’s equations for a spinning black hole, giving us what is now known as the Kerr metric.
The first black holes to be discovered were 10 or 20 times the mass of the sun; the husks of massive stars that burn fast and quickly die. But there’s another category of black hole in our universe — the supermassive black holes that live at the hearts of galaxies.
And it is these giants that we are about to see, as it were, in person.
The coming images have been captured by the Event Horizon Telescope, a network of radio telescopes stretching from the South Pole to Greenland that can operate as a single instrument. This composite telescope has been trained on the centre of our own Milky Way galaxy, and the much more distant heart of the giant elliptical galaxy M87.
The Milky Way’s black heart corresponds to an object weighing millions as much as our sun; and that of the M87 galaxy amounts to billions of times the weight of our sun. Perhaps poetically, they sit at either end of a similar scale to the dark stars originally imagined by Michell.
And, since astrophysical black holes are likely born spinning (since they inherit the rotation of whatever produced them), the images we are about to see may reveal not just a black hole, but a black hole for which the Kerr metric is a key part of our ability to understand it.
Of course, “seeing” a black hole is a paradox. What we see is the matter circling its event horizon, caught in the grip of the black hole’s gravitational field, a spinning vortex around a cosmic plughole. Detailed images of this accretion disk alone would be spectacular enough, but on top of that, we will it apparently twisted into fantastical shapes as the light is pulled and twisted along complex paths in the vicinity of the event horizon.
These images will test Einstein’s understanding of gravity, and provide unprecedented proof that black holes truly exist in our universe. Because seeing really is believing. Even for scientists.
Header image: Oliver James et al 2015 Class. Quantum Grav. 32 065001
Each galaxy lives within its own three-dimensional halo of dark matter whose gravitational field corrals the stars within it. Without the stars, the halo would still be there, albeit invisible to our eyes; but if the halo vanished, the stars would scatter into the depths of the universe – just as a Christmas tree remains a tree with or without the pretty lights. Whereas without the tree, the lights would merely be a puddle of colour on the snowy ground.
Growing up in the Southern Hemisphere, the traditional trappings of Christmas were always out of step with the onset of summer around us: Santa in his cozy suit, imagery of roaring fireplaces, snowy scenes on Christmas cards, a heavy meal we consumed on a hot day before a swim.
But after I’d experienced my first Northern Hemisphere Christmas in Ithaca, New York — which, with several feet of snow on the ground, was something close to Narnia — the childhood strangeness of that transplanted holiday melted away and the seasonal symbolism at last made sense. A festival of light in the darkness of midwinter; gathering around a warm hearth while it snowed outside.
Fast forward a few years and I was living in New York City, where the Rockefeller Christmas tree (and the ice skaters beneath it) stands as a marker of the turning seasons. Another few years further on, my family and I were living in Connecticut, where the town of New Haven marks the season by selecting an enormous local evergreen to make the ultimate sacrifice in exchange for the chance to stand, dramatically lit, in the New Haven Green through the Yuletide season. We lived close by, and it became an annual ritual to walk to see the tree with the kids, always in winter jackets, often with snow on the ground.
New Haven Green. Image: Richard Easther
Once, as we approached the illuminated tree, my wife Jolisa – a literature person, never not searching for metaphors to help make sense of science – asked: “You know this dark matter stuff that you talk about, is it something like a Christmas tree at night — we can see the bright twinkling lights, but we can only make sense of why they’re hanging in the air in that shape if we know about the tree that holds them up?”
And she was exactly right.
Our sun is one of roughly 100 billion stars in the Milky Way Galaxy, and the Milky Way is itself one of roughly a trillion galaxies in the visible universe. For over 100 years, astronomers and physicists have been trying to understand how galaxies, the giant islands of stars that are the large-scale buildings blocks of the universe, hold themselves together. If galaxies are made entirely of stars – in other words, if what we see is all we’ve got – the stars would be moving too fast for their mutual gravitational attraction to hold a galaxy together.
A selection of galaxies; each image contains over a hundred billion stars.
To make sense of this, the vast majority of astrophysicists and astronomers have come to believe that the cosmos is now contains far more than our eyes can see. As we now see the universe, each galaxy lives within its own three-dimensional halo of dark matter, whose gravitational field corrals the stars within it. Without the stars, the halo would still be there, albeit invisible to our eyes; but if the halo vanished, the stars would scatter into the depths of the universe – just as a Christmas tree remains a tree with or without the pretty lights. Whereas without the tree, the lights would merely be a puddle of colour on the snowy ground.
So if you are seeking a secular interpretation of the iconography of Christmas, you could do worse than seeing a well-trimmed Christmas tree, illuminated with lights and bedecked with tinsel, as a metaphor for the cosmos.
Dark matter – by definition – neither emits nor absorbs light, and cannot thus be made of atoms, or indeed any of the fundamental particles known to physicists; it must be something entirely novel. So likewise, let the spectacle of a galaxy serve as a reminder that there is literally more to the physical world than meets the eye, and that there are deep mysteries for us to solve in the years and decades to come.
Happy holidays and compliments of the season.
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The Milky Way over Portobello, Dunedin. Image: Ian Griffin.
Footnote: Actually this sort of was my TED talk. And, full disclosure, we can’t (and shouldn’t) be sure about dark matter until we have a better idea of its properties and composition.
Last weekend. former astronaut, fighter pilot and David Bowie fan, Commander Chris Hadfield posted some stats about the safety of flying, showing that per mile traveled, planes are about 10 times safer than trains, and 100s of times safer than cars.
If you’re afraid of flying, this might change your mind. pic.twitter.com/Ja8Qq1E60I
— Chris Hadfield (@Cmdr_Hadfield) August 31, 2018
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Planes travel further and faster than cars and motorcycles, and that got me to thinking about the safety of all kinds of travel.
Space travel certainly looks pretty risky, and astronauts are selected for their ability to stay calm in the face of danger. But just how risky is spaceflight, by Hadfield’s measure? It turns out that human beings have spent a total of 144.1 years in space.* An astronaut orbits the earth at around 18,000 miles or 28,000 kilometres / hour, so the total distance covered by human beings in space is about 35 billion kilometres.** On the other side of the ledger, 18 astronauts have died in flight (excluding those deaths that happen in training and testing, such as the Apollo 1 fire), making for roughly one death per 2 billion kilometres traveled. In Hadfield’s units that’s about 0.8 deaths per billion passenger-miles, putting space travel in much the same category as riding the subway.***
The second thing we learn from Hadfield’s numbers is that it is not just planes that are safe. By this measure, commercial or public operators (trains, buses, planes) are all safer than cars by at least a factor of 10, and are vastly safer than motorcycles. Hadfield shared his numbers to reassure nervous fliers. But because we are nervous about flying, we have – as a society – insisted that commercial flying be as safe as it can possibly be. People launching rockets likewise go to enormous lengths to make safety a paramount priority.
Conversely, cars actually come out looking pretty dangerous for those inside them. On top of that, Hadfield’s numbers make no mention of deaths among bike riders and pedestrians, most of which result from collisions with motor vehicles. On a per-mile basis, pedestrians and cyclists are killed about ten times as often as people in cars, although this varies vastly by location.
How can this happen? Cars are designed and built using the latest technologies, with all manner of safety features as their selling points. But unlike trains, planes, buses – and spacecraft – cars are vehicles that are typically operated by their owners, and thus mostly driven by amateurs like you and me, on roads that are too often designed to facilitate speedy travel.
As a result we kill ourselves, our passengers, and other people on the road at a rate that would be unacceptable for commercial operators, or even for astronauts flying in space.
That “we” is important, because human beings are terrible at statistics and great at fooling ourselves. “We” don’t get behind the wheel expecting to kill ourselves or someone else, so we don’t necessarily see solving this problem as a priority.
However, many cities and countries around the world are now talking about Vision Zero; the position that traffic fatalities of all kinds are not an unavoidable nuisance, but a menace that can be eliminated through good design, policy choices and decent engineering. People aren’t perfect, but the idea is that – as in the workplace – nobody should pay for a mistake with their own life or somebody else’s.
The key first step is to SLOW DOWN; a collision between a car and a person at 50 km/hr is far more likely to be life-changing or lethal than one at 30 km/hr. That’s just the laws of physics. And safer road design helps make safer speeds intuitive. Also, making it easier for people to use “active modes” (bikes and walking), and improved access to public transport can all make a huge difference to our collective safety on the roads and our personal and social wellbeing in general – by helping us shift from less safe modes to ones that are not only safer, but better for us and incidentally, the planet.
It is easy to make rules for pilots and airlines. The challenge of Vision Zero is that it asks us to make rules for ourselves. But just imagine living in a world where walking and biking was as safe – by Commander Hadfield’s measure – as flying in space.
As the Six Million Dollar Man put it: we have the technology. All we we need is the will to use it.
CODA: There is a lot to say about the coming era of commercial suborbital spaceflight, which will make for a lot of new “astronauts”. And then there is the whole separate topic of self-driving cars, which are often touted as a boon for safety – but an urban environment with people walking and biking on the streets is far more challenging for autonomous vehicles than the highway. The question may be whether these cars can adapt themselves to human cities, or whether their designers will attempt to reshape cities to better accomodate autonomous vehicles – just as the first carmakers did a century ago.
IMAGE: The header image shows the failure of the Antares 3 launch vehicle; the image is from Wikimedia and was taken by NASA/Joel Kowsky.
* That link refers to “man years”. Sigh.
** This does not account for the small number of astronauts who traveled to the moon; they move faster than orbiting astronauts at the beginning and end of their trips, but more slowly in the lunar environment.
*** The total number of “astronauts” includes people who achieved an altitude of 100km or more during suborbital flights – the so-called Karman line at which aerodynamic control becomes impossible and space effectively begins. It’s also worth noting that Hadfield’s statistics are per mile, not per trip. Plane trips are much longer than car trips so this statistic makes each individual flight look safer than a typical journey by car; if the average car trip is a few kilometres and the average plane ride is more like a thousand kilometres, the risk per trip is actually roughly similar for cars and planes. Those 18 astronaut deaths occurred among the roughly 560 people who have been into space, putting the overall death rate per participant at about 3% and at maybe 1% per trip (since some people have made multiple flights) which of course puts the safety of space travel in a very, very different light. Lastly, the deaths all occurred during launch or reentry so it’s not being in space that is dangerous, its getting there and coming home.
This is the week the Nobel Prizes are announced, and today is the day (at least in New Zealand; first place in the world to see the light, as the tourist people say) the Physics prize is announced. And this year the odds-on favourite will be LIGO and the discovery of gravitational waves.
It is possible that the famously cautious Nobel committee will wait another year but their biggest debate may be exactly which people should get the nod, as the prize can only be split three ways. At one point the LIGO experiment was driven by “the troika” of Rainer Weiss, Kip Thorne and Ronald Drever which would have simplified matters. However, Drever was sidelined early in the process and died this year, rendering him definitively ineligible and leaving an empty chair. One candidate to fill it is Barry Barish who is credited with laying the much of the groundwork for the overall LIGO collaboration but there is no shortage of claimants.
This gets to the heart of a dilemma with prizes and the Nobel in particular, thanks to the almost infinite prestige it confers upon winners and the iron rule that it can be shared only three ways: we award accolades to individuals for what are ultimately the accomplishments of a community. One solution would to give prizes to ideas; there is often debate about who should win the prize but it is rare to hear deep disagreement as to what should win the prize. Nor do we honour the often unsung heroes who make the community tick. [My proposal for a George Bailey Prize has gone nowhere, however. C’est la vie.]
But ahead of the big reveal, here are a few quick thoughts:
As it happens, I have been teaching about gravitational waves over the last few weeks. At the University of Auckland (where I am Head of the Department of Physics, or “Chair”, in North American parlance) we were grappling with a paradox at the heart of all physics programmes: we like to think of physics as a cutting edge discipline but the foundational material we teach to undergraduates has almost all been known for decades or centuries. In fact, even “modern physics”, quantum mechanics and relativity, was itself developed in the 1920s, and is perhaps “modern” in the same way that Virginia Woolf and TS Eliot are “modernist writers”.
Our solution to this dilemma was to develop a second year / sophomore course we called “Frontiers of Physics“, which treats cutting edge topics but assumes only introductory physics. This comes at the cost of the finer details, but in the case of gravitational waves you can get a lot of traction with the key ideas of energy conservation, the wave equation, the interference of light beams, and a little special relativity. This year is the first time we have taught the course and gravitational waves have truly been ripped from the headlines: I had to change my lectures to keep up with breaking news from LIGO and discoveries in black hole physics. And I couldn’t be happier.
CODA: The header image is from the Simulating Extreme Spacetimes (SXS) Project. And this post was edited a little to clarify the reasons why Roy Kerr is not tipped to win the Prize today. (Thanks to Christopher Berry for comments on Twitter about this.)
It has been a bitter-sweet month for solar system explorers.
As a teenager and a space-geek, I had a poster of this iconic montage of montage of Saturn’s moons, composed from images taken by the two Voyager probes as they rushed past the ringed planet.
Time passes. In August, the Voyager mission celebrated its 40th anniversary; the twin spacecraft are heading into interstellar space but still regularly dispatch data to Earth, their signals growing fainter and fainter as they travel further and further from home. With luck they will survive another decade, but they must eventually fall silent and will journey mutely to the stars.
This week on September 15, the Cassini spacecraft – the most recent visitor human beings have sent to Saturn – will meet a far more emphatic demise. Launched 20 years ago, Cassini arrived at Saturn in 2004 and took up orbit around the giant planet, making hundreds of loops through its retinue of moons and skimming the iconic rings. It’s about to run out of the propellant needed for manoeuvring; theoretically it might circle Saturn forever, but we could no longer steer it.
So, as I write this, Cassini has climbed away from Saturn for the final time to make a flyby of Titan, Saturn’s largest moon, which has nudged it into a collision course with the giant planet.
Cassini’s spectacular finale is, in part, a tribute to its success. All spacecraft carry stowaways: bacterial spores which can, remarkably, remain viable in the vacuum of space. And one of Cassini’s many discoveries was that three of Saturn’s moons appear to have oceans of water beneath their solid crusts. Leaving the spacecraft to wander unguided around the Saturnian system would risk a collision with one of these moons. So, rather than let its microbial hitchhikers disembark onto a pristine world, Cassini will not “go gentle into the good night” as its propellant runs low but has been steered towards a fiery demise.
Geysers of warm water from the sub-surface oceans of Enceladus.
For cosmologists like myself, the contents of our own solar system (and even our own galaxy, much of the time) are things to look past rather than to look at. The complex worlds that circle our sun can seem to be a motley collection of adorable oddballs when compared to the deep simplicity of the universe itself, like Shakespearean comic turns in the foreground with the serious actors behind.
If cosmologists were architects, I supect most of us would be austere modernists, whereas planetary scientists might prefer rococo delights adorned with complicated facades and gratuitous flourishes.
Saturn’s moon Mimas, with the impact crater Herschel.
Saturn is a prime example: beyond its gaudy rings and complex cloud tops, it boasts an astonishingly diverse collection of moons. These include Titan, the only known moon with its own atmosphere, to which Cassini dispatched the Huygens lander; and Mimas, a battered icy world sporting a giant impact crater that makes it look uncannily like the Death Star. (“That’s no moon, it’s a space station” – and yet this, indeed, is a moon.)
NASA has an undoubted ability to sell a story, and it has been making the most of the anthropomorphic appeal of this brave little $3 billion, 5 ton, plutonium-powered spacecraft on its two-decade mission. But the hype is not misplaced: Saturn has a key place in the evolving human understanding of the cosmos. “Childlike wonder” is both a cliché and the literal truth when we speak of the “space”. The most distant planet easily visible to the naked eye, Saturn once marked the apparent edge of our solar system. Its rings are visible through even the smallest of telescopes, and seeing them this way still takes my breath away. Cassini has shown us Saturn with its rings and its moons up close and personal, with astonishing clarity and precision. The spacecraft and the team of scientists responsible for it have written themselves into the history books.
Beyond revealing the universe to us, space exploration exposes our own small place in the big picture. Saturn’s rings, backlit by the distant sun, dominate what may be the most haunting image returned by Cassini. After taking in the planet’s dark bulk and golden rings, our eye drifts to the pale blue dot in the lower right hand corner of the frame, and the image’s full weight is revealed: it is a lovely, lonely, long-distance portrait of the Earth and of humanity itself.
The earth, as seen from Saturn.
CODA: All images courtesy of NASA, JPL and/or the ESA. The header image is from a visualisation of Cassini’s final plunge into Saturn’s atmosphere.
As a physicist, Saturn always stuns me with the complex orbital dynamics of its moons, the chaotically braided and filigreed rings, and its astonishing atmospheric dynamics. Truly, there is something here for everyone.
