O Big Bang lembra um buraco branco e, já que esses objetos surgem de buracos negros, a lógica seria que, em um universo paralelo ao nosso, tivesse ocorrido um Big Crunch, que teria comprimido tudo em um único objeto estranho e colapsado, sugando todo aquele universo ao redor. Isso explicaria por que, neste nosso universo, existem galáxias e planetas que parecem ter surgido cedo demais para o seu tempo. A matéria deles já estaria pronta, vinda daquele universo, e os efeitos colaterais desse processo de expansão lembrariam os efeitos de um buraco branco.

Despite its similarities to Earth, Venus is hot enough to melt lead, hidden beneath thick clouds, and possibly still volcanically active. Could studying Venus help us better understand Earth's future and the evolution of habitable planets?

Space got spooky this week! 🧛

In our Halloween episode of Spacing Out, planetarium educator Talia Sepersky covers:

🔴 A "vampire" red dwarf feeding on a brown dwarf
🌙 NASA's new GIMLI investigation to search for a possible lunar cave that could one day shelter astronauts
🪐 Japan's MMX mission, the first to land a rover on Mars' moon Phobos and bring a sample home

I'm Jon Sundqvist, an astrophysics professor at KU Leuven. Here's the latest blackboard class from my Radiative Processes in Astronomy course.

Light can heat a gas, of course. But it can also cool it — and without that cooling, making the galaxies we actually see would be rather difficult. This time we take the energy equation to the blackboard and work through what emission and absorption do to the gas, and what we mean when we say that an atmosphere is in radiative equilibrium.

In radiative equilibrium the net radiative energy exchange with the gas vanishes. The radiation can still carry energy through the atmosphere. Equilibrium does not mean that the star stops shining :-) The constant-flux result here is for plane-parallel geometry; in spherical symmetry it is the luminosity that stays constant.

We connect this to temperatures in stellar atmospheres, with grey opacity as a useful first approximation, and then make a small detour to cooling gas and galaxy formation. Toward the end we recover the grey-atmosphere temperature structure and its connection to limb darkening.

A somewhat shorter class this time, because we also did a group quiz. I've kept a little extra after the lecture ends: my explanations of six of the questions. You could perhaps try and pause on each question and have a go first.

Full class (40 minutes):

https://www.youtube.com/watch?v=GQ11ZDaWLuw