Brilliant Blue Dot

From the past two weeks:  Sun-like stars up to around 8 times the Sun’s mass will evolve into a white dwarf surrounded by multiple shells of glowing nebulae, and called planetary nebulae. Stars more massive than 8 solar masses and up to 25 solar masses evolve explosively into neutron stars with a singular shell of debris expanding at a high rate of speed.

White dwarfs are held up by electron degeneracy pressure and are about the size of Earth. Neutron stars are held up by a combination of neutron degeneracy pressure and nuclear forces and are about the size of Canyon Lake. Thinking about it this size comparison is relevant to the structure of an atom. Visualize a giant atom – a shell of electrons the diameter of Earth, with its nucleus in the center, the size of Canyon Lake. That’s an example of how atoms are mostly space.

Neutron stars are very hot, around 600,000 K, much hotter than a white dwarf’s 40,000 K, and they shine blue – white. With a surface temperature of around 600,000 K current models predict an atmosphere, yes an atmosphere, possibly of lighter element nuclei such as helium. An atmosphere yes, but only a few micrometers thick.

The surface of a neutron star theoretically is a lattice of iron nuclei with electrons flowing through gaps. For higher temperature neutron stars such as pulsars the surface might even be a fluid. The interior of a neutron star is more enigmatic. Exotic forms of matter pervade as density and pressure crush nuclei, leaving neutrons. Toward the core, we just don’t know what’s going on and it’s mostly conjecture. The makeup of a neutron star’s core could be the strongest stuff in our universe, astrophysicists sometimes call “nuclear pasta”, super dense. Another hypothesis is that of a superfluid core made of neutron-degenerate material. Even more exotic matter such as quark-degenerate matter, pions, or kaons might be present in this superdense core.

All this density produces a mass roughly equal to the Sun in a little ball the diameter of Canyon Lake! With this high density and mass comes immense gravity. A neutron star’s gravity is so strong that it is a gravitational lens, bending the path of photons. In some cases, its own photons get trapped in orbit and the neutron star’s entire surface becomes visible, weird! The origin of their super strong magnetic fields is enigmatic, however. Neutron stars with ultra-extreme magnetic fields exist and are called magnetars. Magnetars are pulsars also, spinning around many times per second with a jet of photon plasma whipping around from their poles. That’s how we found pulsars, we’re in the direction of some of that plasma. A magnetar is so extreme it has star quakes, where its magnetic field causes surface fractures.

To be continued…

What’s in the Sky?

April 25-27; pre-dawn; east: The waning crescent Moon interacts with Venus, Jupiter, Mars and Saturn

April 29; dusk; west: Mercury is just left of the Pleiades