Hubble provides fresh insights into "standard candle" supernovae
The Hubble SpaceTelescope has granted astronomers fresh insights into a specialfamily of supernovae that represent a vital tool for measuring vast cosmic distances. The discovery revolvedaround observing the aftermath of a Type Ia supernova and analyzing theproperties of the residual light.
The significance ofType Ia supernovae is that they are predictable. The vastexplosions are believed to occur when a white dwarf in a binarysystem siphons enough stellar material off of its companion to reachwhat is known as the Chandrasekhar limit.
Once this occurs, athermonuclear explosion is inevitable. The light from this explosionis somewhat of a known quantity, allowing astronomers to observe theextent to which the light has dimmed before it reaches Earth, andfrom this, work out the distance to the supernova.
For the new study,Hubble focused on SN 2012cg, a type Ia supernova located roughly 50million light-years away from Earth in the galaxy NGC 4424. Previousresearch had indicated that roughly 500 days after the first light ofa type Ia supernova reaches our telescopes, the residual light wouldstart to fade.
This is known as the "infrared catastrophe," which was believed to occur as thehalf life of the nickel isotope 56Ni, a heavy element created in thedramatic supernova, comes to an end, ultimately transitioning into amore stable iron isotope.
However, this drop offhas never actually been observed, leading some astronomers to theorize in 2009 that the prolonged light was thrown off from aheavier form of a cobalt isotope with a longer half life known as57Co.
Observations of SN2012cg that were carried out three years after the light of theviolent explosion reached Earth supported the theory, albeit with aninteresting twist. According to an analysis of the residual glow,there would have had to have been twice the amount of 57Co than hadpreviously been believed in order to account for the light outputthat long after the initial explosion.
There are still a great number of unknowns regarding the supernovae. For example, as it stands astronomers assume that Type Ia supernovae discovered in the local Universe result from the same type of star and type of explosion as those that occured earlier in the lifespan of the cosmos. Should either of these assumptions be proven incorrect, it would introduce a fundamental inconsistency in the way we measure the distances between galaxies.
The new research will attempt to mitigate one area of uncertainty by constraining the explosion models of Type Ia supernovae. The discovery that the powerful explosion of SN 2012cg produced significant quantities of 57Co will allow astronomers to focus on models that successfully predicted higher ratios of the element. This new insight will ultimately allow astronomers to make more accurate measurements of vast cosmic distances, and a better understanding of the expansion of our Universe.
However, there is apossibility that the drop off in light did occur as previouslytheorized, and that the light detected in recent observations was simply a"light echo." This occurs when light from the originalexplosion strikes a dust cloud. This cloud refracts the light,scattering it in all directions and causing it to arrive at Earth asan echo years after the first detection of the event.
A paper on the study is available online in the Astrophysical Journal.