October 26, 2012
White Widow Theory Could Explain Type Ia Supernovae Birth
Lee Rannals for redOrbit.com - Your Universe Online
There are two models today that attempt to explain how Type Ia supernovae are born, the first being "single-degenerate model."
In this model, a binary star is made up of a degenerate, or dead star, called a white dwarf paired with a younger star. Over time, as the stars orbit each other, the white dwarf's gravity siphons gas from the atmosphere of its partner star until the white dwarf becomes so massive and dense that it ignites.
The other theory for building a Type Ia supernovae is known as the "double-degenerate model." In this model, it takes two white dwarfs in a binary system spiraling together and colliding to create a Type Ia supernova.
Wheeler claims that the telescope data does not support either model completely.
"I believe that the spectra have to be respected,” Wheeler said in a prepared statement. "The really high-order constraint [on a supernova model] is to get the spectral evolution correct. That is, you've got to get all the bumps and wiggles, and they've got to be in the right place at the right times."
He said that he has a new twist on the single-degenerate model, pairing the white dwarf with an M dwarf.
"M dwarfs are the most common star in the galaxy, and white dwarfs are the second-most common star in the galaxy,” he said. “And there's lots of M dwarf-white dwarf binary systems. Do they make Type Ia supernovas? That's another question."
Astronomers using large telescopes have looked at the gaseous remnants left behind by Type Ia supernovae for the partner star that would be left behind, and Wheeler says they aren't finding it.
Small red M dwarfs are dim enough to where even the most massive types would not show up in the Hubble Space Telescope observations.
Wheeler said that the white dwarf could have devoured the entire M dwarf before the white dwarf exploded, and that M dwarfs do not have heavy cores to leave behind.
He calls his new scenario a "white widow system," which is a play on words referencing "black widow systems."
Another reason for the M dwarf being the likely co-parent is that they are magnetic, meaning both parent stars would be magnetic.
Wheeler said if a magnetic white dwarf and a magnetic M dwarf are a binary star pair, their opposite magnetic poles would attract, and they would become tidally and magnetically locked into a rotation in which the same side of each always faces the other, and the magnetic poles point directly at one another.
Under this scenario, the white dwarf still pulls material off of the M dwarf, but the material would build up on a single spot on the white dwarf that pointed right back at the M dwarf, irradiating it and driving off even more mass, consuming the M dwarf.