November 19, 2018

08.05.10: Does Type Ia Supernova Formation Need Revision?

A key measurement device used by modern astrophysicists may also hold an elusive mystery. It has been long known that a Type Ia supernova occurs when a white dwarf accretes in-falling material from a binary companion, grows past the Chandrasekhar limit of 1.4 solar masses, and promptly blows itself up in a thermonuclear chain reaction that can be seen across the universe. These brilliant displays rise in brightness and then fade in a predictable fashion, allowing them to serve as “standard candles” marking the intergalactic distances to their host galaxies. These accreting white dwarfs should give off copious amounts of X-rays leading up to their eventual ignition. If this is the case, where are these accreting white dwarf SN Ia’s in waiting? An interesting study was released earlier this year by Akos Bogdan and Marat Gilfanov of the Max Planck Institute. Analyzing five elliptical galaxies and the nearby Andromeda with NASA’s Chandra X-Ray observatory, they found X-Ray output to be up to 50 times less than expected if the seeds for Type Ia’s were indeed being sown. Several factors may account for this discrepancy;

  1. Perhaps energetic accretion is not a constant state in these binary systems;
  2. The types of galaxies surveyed (with the exception of Andromeda) are not known for their energetic star formation;
  3. Type Ia’s may be more prevalent during certain epochs of star formation in the universe;
  4. Other mechanisms, such as merging white dwarf binaries, may produce Type Ia supernovae without accretion. But these populations would surely be lower throughout the universe than mixed systems; it isn’t even clear if a merging white dwarf pair would explode, or simply collapse into a neutron star. And white dwarfs are just plain tough to spot at galactic distances!

Whatever is the case, there still isn’t a consensus in the astronomical community as to where the Type Ia’s-in-waiting are hiding. It should be noted that this controversy does not center on the luminosity relationship;   naysayers look elsewhere for your chink in the frame-work of the Big Bang Theory! Instead, we suspect that “sub-breeds” Of Type Ia (Type IAa?) supernovae will come to light as new platforms such as James Webb Space Telescope come on line in the next decade.

Astro-Challenge:Spy a White Dwarf!

This week, I’m going to introduce you to a unique but fascinating multiple star system, and one that’s definitely worth seeking out as it’s a good study in comparative stellar evolution; Omicron Eridani. This one will require a telescope of about 4′ aperture or greater, a go-to scope or a good finder chart, and patience. But the quarry is worth it; for Omicron Eridanus B is a white dwarf, the most easily observable in the sky, paired with C, a red dwarf star! Omicron Eridani is a triple star system, about 16.5 light years distant. The primary star, a K type main sequence star, is visible to the naked eye at a magnitude of about +4.5. Known to the Arabs as Al Keid (“the Egg”),

[Read more...]