One disk, two disks, red disk, blue disk?

It is written in The Standard Lore of Astronomy – a leather-bound book professors keep under their desks – that stars in the disks of spiral galaxies have a bimodal distribution of scale heights. Today we will be discussing a paper that comes to the conclusion that the notion of a thick disk and a thin disk is actually a poor approximation to the true distribution of disk stars.

Were the First Stars Actually Hypermassive?

Were the First Stars Actually Hypermassive?

Paper title: Protostellar Feedback Halts the Growth of the First Stars in the Universe Authors: Takashi Hosokawa, Kazuyuki Omukai, Naoki Yoshida, Harold W. Yorke Author’s Affiliation: Jet Propulsion Laboratory; Department of Physics, Kyoto UniversityThe problem of understanding the formation and evolution of the first to form stars in the universe lies at the intersection of many fields of astrophysics. Since the first stars could only have formed once their host dark matter halos had begun to collapse, one must understand the formation of these stars in a cosmological context, tracking gas from extremely low intergalactic densities (~10-27 g cm-3), to extremely high, stellar densities (~1 g cm-3). Since all the metal content of the universe had not yet been synthesized in the cores of stars, the gas that collapsed to form the first stars would have been metal-free and thus possessed very different thermal properties compared to the interstellar and intergalactic gas in the local universe that can cool via metal line emission.Many studies of first star formation have focused on the cosmological piece of the puzzle: starting with a simulation of cold dark matter and gas in a ΛCDM cosmology, they look for the first ~106 solar mass dark matter halo to collapse, and then follow the collapse of first the dark matter and then the gas to very high densities. Due to the extremely large dynamic range in these simulations, it becomes prohobitively expensive to reach stellar densities and impossible to directly model the evolution of the first star. For reference, a recent simulation of the formation of the first stars followed the collapse to densities just above 10-8 g cm-3, far below typical stellar...
Lighting up Simulated Galaxies

Lighting up Simulated Galaxies

For today’s astrobite, we will be discussing some of the highest-resolution simulations of isolated galaxies performed to date. Not only are these simulations high resolution, but they also include prescriptions to model several physical effects that previous galaxy evolution simulations have mostly ignored.

The Limitations of Smoothed Particle Hydrodynamics

The Limitations of Smoothed Particle Hydrodynamics

Smoothed Particle Hydrodynamics (SPH) is one of the most commonly used techniques for simulating astrophysical fluids. This particular paper focuses on a regime of gas dynamics that is often neglected in astronomy: subsonic turbulence. Just as the air in the upper atmosphere exhibits random motions that can buffet an airplane cabin, the gas in interstellar space also exhibits random, turbulent motions.