Astronomers have reported a whole new type of exploding star, or supernova, which seems to spew out calcium and titanium. While most press reports have focused on the calcium, it's the titanium that's really interesting - the finding could negate ongoing efforts to find signs of dark matter at the center of the Milky Way.
The team of astronomers, led by Hagai Perets, now at the Harvard-Smithsonian Center for Astrophysics, and Avishay Gal-Yam of the Weizmann Institute of Science in Rehovot, Israel, presents evidence that supernova SN 2005E is distinct from the two main classes of supernovae: the Type Ia supernovae, thought to be old, white dwarf stars that accrete matter from a companion until they undergo a thermonuclear explosion that blows them apart entirely; and Type Ib/c or Type II supernovae, thought to be hot, massive and short-lived stars that explode and leave behind black holes or neutron stars.
Perets and colleagues describe a scenario with a pair of orbiting white dwarf stars, where one SN 2005E and arguing that it is distinct from the two main classes of supernovae: the Type Ia supernovae, thought to be old, white dwarf stars that accrete matter from a companion until they undergo a thermonuclear explosion that blows them apart entirely; and Type Ib/c or Type II supernovae, thought to be hot, massive and short-lived stars that explode and leave behind black holes or neutron stars.
One theory of this new exploding system is that a low mass white dwarf steals helium from a companion until the mass thief becomes very hot and dense until the temperature and pressure ignited a thermonuclear explosion – a massive fusion bomb – that blew off at least the outer layers of the star and perhaps blew the entire star to smithereens. The helium is transformed into elements such as calcium and titanium, eventually producing the building blocks of life for future generations of stars.
The titanium is radioactive and emits positrons as it decays. Over the past couple of years, there have been reports from experiments such as ATIC and PAMELA of an excess of positrons coming from deep space. This excess, it has been argued, is a signature of dark matter particles colliding. But if the new supernova finding is anything to go by, these explosions could be quite commonplace and they could be the source of the excess positrons.
While this does not prove or disprove the existence of dark matter, it challenges the interpretation that the excess positrons are coming from the annihilation of dark matter particles. The WMAP, which supports the "concordance (Λ-CDM) model" of the Universe with up to 73% dark energy, 23% dark matter and 4% comprising all the matter in observable universe, has been under attack. Critics state that claims for the existence of invisible, unknown forces, to support a Big Bang theory where it is admitted that over 90% of the universe it seeks to explain cannot even be detected, is not what Karl Popper would have called "science.".
Casey Kazan via http://www.newscientist.com/blogs/shortsharpscience/2010/05/new-supernova-class-may-underm.html