The Week in Space and Physics: A Model Universe
The Week in Space and Physics: A Model Universe
On simulating the cosmos, colliding planets, the age of the Moon and an icy supervolcano.
Fourteen billion years ago, if cosmologists are right, the universe began with the Big Bang. Out of it poured all the things that make up matter - all the electrons and neutrinos, quarks and bosons - as well as more elusive things - the dark matter and dark energy - that we think shape the cosmos.
Over billions of years those things came together to build larger structures: atoms, stars, galaxies and more. Today the cosmos appears to be ordered on a grand scale, composed of galaxies in clusters and clusters in superclusters. Behind it all lies a scaffolding of dark matter holding the galaxies together and connecting them through hidden threads.
The job of the cosmologist is to understand how we got from one state to the other. How, in other words, did individual particles come together to create the universe we see today? To find out, they turn to general relativity - our most complete theory of gravity - and study how matter moves under its equations.
That, however, can only take you so far. To properly study the evolution of the universe we need to know not just the forces that shape it, but also the sum of the things in it. For that cosmologists often turn to computer models.
These models simulate the evolution of the cosmos from the Big Bang to the modern day. But, crucially, they allow cosmologists to play with the details of that evolution. They might, for example, alter the balance of matter, dark matter and dark energy, and then see what kind of universe comes out. The ultimate goal is to find a set of parameters that create something close to what we actually live in.
FLAMINGO, the most complex model yet run, did this by modeling hundreds of billions of galaxy-sized “particles” moving through a cube some ten billion light years across. The team behind the project, based in the Netherlands, last week released the first set of results from the simulation - some of which you can view here.
FLAMINGO has also included several effects that were mostly ignored in previous simulations. Some of these - like the winds blowing out of galaxies, or the effects of fleeting neutrinos - are known to have had a large impact on how the universe evolved. But they are also more complex to model, and so had to wait for the availability of more powerful computers.
The FLAMINGO team has already rerun the model more than two dozen times. Each run varies the parameters used, resulting in a slightly different cosmos each time. Those predictions will soon be compared with real world data, including that coming from Euclid, a new space telescope.
Since Euclid will map out the positions of billions of galaxies, its data should provide a guide as to which models are correct. That, in turn, should show which assumptions about the universe are right - and which are wrong.
When Planets Collide
Long ago, we think, two planets in our solar system smashed into each other. One, named Theia, was about the size of Mars. The other - which we name proto-Earth, since it was not yet the planet we call home - was probably slightly smaller than the modern Earth.
The collision obliterated both planets, turning them into a cloud of molten rock and debris. Over time they coalesced, forming the familiar outlines of the Earth and the Moon. This violent origin story explains many oddities about our planet and its satellite; from the large relative size of the Moon to the similar make up of their crusts.
Now astronomers reckon they’ve spotted the same thing happening around a far away star. That story began in December 2021, when a network of telescopes saw a star suddenly fade away. After examining it more closely, astronomers realised their data showed another strange event. In 2019 the same star had briefly emitted a pulse of infrared light, corresponding to a release of heat measuring several hundred degrees.
Taken alone, these two events could have several explanations. But put together, they suggest that two planets collided around the star in 2019, creating a vast cloud of debris that blocked out the light coming from the star. Both planets, in this case, seem to be larger than the Earth, probably measuring somewhere between the size of Earth and Neptune.
Analysis of the temperature of the impact shows that this probably wasn’t a head on collision. Instead one of the planets likely struck the other with a glancing blow, just as Theia may have once done to the proto- Earth. The result, if this is the case, would be a doughnut shaped cloud of debris that slowly coalesces into a planet and a large moon.
Astronomers reckon that the Earth only took about a century to reform after the Theia impact. Whether the same will be true for these planets is so far unclear - though astronomers, surely, will be watching to find out.
How Old is the Moon?
Until astronauts visited the Moon in the 1960s and 70s, we were uncertain how the Moon was formed. The rocks they found there - which showed striking similarities to those on Earth - lent support to the idea the Moon and Earth had formed together. Other evidence, such as that from an analysis of zinc isotopes on the Moon, helped pin the blame on Theia.
Now, a new analysis of moon rocks has helped fix the date of when this happened. When Theia smashed into the proto-Earth, the two planets were shattered; blown into a cloud of molten metal and rock. When the debris began to cool and solidify, crystals started to grow inside the newly forming rocks. Those crystals contained traces of radioactive elements which - since they decay over time - act as a kind of clock.
On Earth few original rocks are left; thanks, of course, to the forces of erosion and tectonic activity. The Moon, in contrast, is unaffected by these things, leaving many of its rocks pristine. Some of those brought back by the Apollo astronauts, therefore, still retain crystals formed as the Moon cooled.
The analysis of those crystals found their age to be 4.46 billion years - showing that the Theia collision must have happened at least that long ago. Since we already know the Solar System was born 4.57 billion years ago, this finding gives a narrow hundred million year range in which the Earth and Moon came to be.
A Supervolcano on Pluto?
When New Horizons flew past Pluto in 2015, scientists spotted signs of volcanoes dotting its surface. Unlike the volcanoes found on Earth, these seem to spew out liquid water instead of molten rock. Since the surface temperature of Pluto is so low, that water acts a bit like lava on Earth and, over time, builds up mountains of ice.
One area of apparent volcanic activity recently drew the attention of researchers. The region, known as Kiladze, has long been known to be dominated by water ice, marking out its volcanic origin. In a recent paper, a group of scientists argued that the region resembles vast supervolcanoes previously seen on both Earth and Mars.
The whole area, they think, is a single volcanic caldera measuring thirty miles across. There are signs that it has erupted relatively recently and that when it did it poured out vast amounts of water. That could make it Pluto’s equal to Yellowstone, a volcanic caldera that has, in past eruptions, thrown out hundreds of cubic miles of rock, ash and lava.