Hexbyte – Tech News – Ars Technica |
Got the blues and a bit shouty —
Helium absorbs light, heats star. Star expands, blows off material, collapses.
The Universe abounds with things that we think we might understand but aren’t really sure about. What it often comes down to is our ability to compute: to answer the question of whether models based on the physics we know about generate the behavior we see around us. In response to that question, researchers have turned their computation gun on a long-standing problem: why do luminous blue variable stars exist?
Luminous blue variables are very big, very bright stars, but their temperature (color) varies quite a bit. Scientists were pretty sure that the variability came down, somehow, to a combination of radiation pressure, shock waves, and convection. But until now, no one could confirm that.
Hexbyte – Tech News – Ars Technica | Emotional stars lose their equilibrium
In particular, luminous blue variables go from brightness and temperature ranges that are in equilibrium to brightnesses that are far out of equilibrium.
What do we mean by that? At the center of any star, nuclear reactions generate light. The light exerts a pressure on the matter in the star that prevents further gravitational collapse. At equilibrium, the radiation pressure balances gravitational collapse, and everything should be nice and steady (as it is with our Sun). The temperature and brightness of the star reflect this balance.
For stars that are much hotter, like the blue end of luminous blue variables, the radiation pressure exceeds gravitational collapse. During these moments, matter is blown off the star like so many dandelion seeds.
The strange thing about luminous blue variable stars is that they irregularly transition between equilibrium and non-equilibrium states. How and why that happens is a long-standing question.
Hexbyte – Tech News – Ars Technica | When in doubt, code
The issue is not one of physics but solving difficult equations. For instance, if you want to understand a star from a mathematical point of view, a few lines of equations solve the problem. But turning those equations into predictive models is difficult.
The common approach is to simplify: stars are spherical, so maybe we only need to care about their depth. By reducing the equations from 3D to 1D—a line from the star’s core to its surface—the math becomes simpler, and we ca