Eight New Quadruple Lenses Aren’t Just Gorgeous, They Reveal Dark Matter’s Temperature
“Ever since astronomers first realized that the Universe required the existence of dark matter to explain the cosmos that we see, we’ve sought to understand its nature. While direct detection efforts have still failed to bear fruit, indirect detection through astronomical observations not only reveal the presence of dark matter, but this novel method of using quadruply lensed quasar systems has given us some very strong, meaningful constraints on just how cold dark matter needs to be.
Dark matter that’s too hot or energetic cannot form structures below a certain scale, and the observations of these ultra-distant, quadruple-lens systems show us that dark matter must form clumps on very small scales after all, consistent with them being born as arbitrarily cold as we can imagine. Dark matter’s not hot, nor can it even be very warm. As more of these systems come in and our instruments go beyond what even Hubble’s capabilities are, we might even discover what cosmologists have long suspected: dark matter must not only be cold today, but it must have been born cold.”
We might not yet know the nature of dark matter, as we’ve never been able to detect the particle responsible for it directly. But we know it clumps and gravitates together, with the exact way it would do so dependent on the amount of kinetic energy it had when it was born relative to its mass. Dark matter could have been extremely hot, such as a scenario where it was made from neutrinos, cold, such as from a very heavy WIMP particle (or a born-super-cold axion), or anywhere in between.
The zeroth law of thermodynamics states that if two thermodynamic
systems are each in thermal equilibrium with a third, then they are in
thermal equilibrium with each other. Accordingly, thermal equilibrium
between systems is a transitive relation.
Ask Ethan: How Can Worlds That Never Get Above Freezing Have Liquid Water?
“I was reading about Saturn’s moon Enceladus, and how scientists believe it has liquid water oceans beneath its water-ice crust. And yet I also read that the warmest surface temperatures are -90 celsius. How can this moon have liquid water? […] At such cold temperatures and low pressures it seems Enceladus can have water ice and water gas but not liquid. What am I missing?”
Here on Earth, water can easily exist in all three phases of matter: solid, liquid, and gas. The reason for this is simple: Earth has the right range of temperatures and pressures to experience not just the common solid and gas phases, but the liquid water phase, too. In the outer Solar System, worlds like Europa, Enceladus, and Pluto are too far from the Sun to ever reach surface temperatures high enough to create a liquid phase; it seems that water is a no-go. But there must be subsurface oceans on these worlds! Not only is there geological evidence of an ocean beneath a thick layer of ice, but on some worlds, like Enceladus, we can actually see large plumes of liquid water ejected hundreds of kilometers above the surface, like some sort of planet-scale geyser. While the increased pressure from the ice plays a role, it isn’t enough on its own; there must be other factors, too.
“Indeed, if there were a conspiracy, if climate science were a hoax, and if all this research were incorrect, all it would take was one scrupulous, competent scientist. But every scrupulous, competent scientist that investigates it has come to the same conclusion: it’s real, it’s warming, and it’s our CO2 that’s doing it. You are free to deny climate change if you want, but there’s no scientific leg to stand on if you do.”
It only makes sense that scientists should debate and argue over the findings in their field. Given all the suites of data available that are relevant to a particular physical phenomenon, how do we put it together in a way that is scientifically robust, allow us to understand and predict what’s happening, and justifiably attribute the causes of observed phenomena? It’s a daunting task, and one that you need science for. So when it comes to global warming, why aren’t the arguments about the temperature and atmospheric concentrations of gases over time? Why are they instead about scientific personalities, profitability, conspiracies and hacked emails? Why, instead, aren’t those opposing the science of human-caused climate change pointing to data and scientific arguments?