August 4, 2012
Subaru Observations Provide 3D Structure of Supernovae
Lee Rannals for redOrbit.com - Your Universe Online
Japanese researchers using the Faint Object Camera and Spectrograph (FOCAS) on the Subaru Telescope have revealed a clumpy 3D structure of supernovae.The finding supports the clumpy 3D scenario of supernovae explosions, rather than the widely accepted bipolar explosion scenario.
The latest research advances the scientific understanding of how supernovae explode, which is a mystery to astronomers.
Stars that have reached a mass weighing heavier than eight solar masses will eventually die through a violent explosion called a supernova. A supernova ejects elements synthesized within its star that are heavier than hydrogen and helium, which are the main elements in the primeval Universe.
The ejection of these heavier elements into interstellar space has enriched the chemical composition of the Universe.
The process of how supernovae explosions occur is unclear, but researchers agree that supernovae would not succeed as one-dimensional, spherical events, and that multi-dimensional effects are important for understanding their occurrence.
Scientists believe two main scenarios take place that explain how supernovae explosions occur.
One scenario is that a bipolar explosion is facilitated by rotation, while the second is a clumpy 3D explosion is driven by convection. Although they believe these scenarios play out, they are not sure which is more plausible, because they have not actually observed the shape of supernovae.
Observing the shape of a supernova is a difficult task, because most of the celestial events occur in galaxies millions or hundreds of millions of light years away. Because of this great distant, they only look like a point.
The Japanese researchers used a special method of detection to reveal the shape of supernovae. They measured "polarization," which helps supply information about the direction of vibrating electromagnetic waves.
The team performed numerical simulations for emissions from supernova and found different polarization patterns for clumpy and bipolar explosions.
An object with various angles of polarization is considered a clumpy explosion, and one with a single angle of polarization is seen in a bipolar explosion.
The group used FOCAS to conduct polarimetric observations of nearby supernovae. These observations measure the intensity and direction of polarization.
Because the team was unsure when the supernovae would appear, they were unable to assign an observing time in advance. Fortunately, the Subaru Telescope's Target of Opportunity (ToO) mode enables a dynamic allocation of the observing time.
The team was able to use this method to succeed in conducting polarimetric observations of two "stripped-envelope supernovae," which do not have hydrogen surrounding them, and are the best targets for studying explosion geometry.
They detected the polarization from the two supernovae, which clearly indicated that the supernovae are not usually round. They also found that each one had various angles of polarization.
Once the team added the two new supernovae to the ones from pervious observations, they had a total of six stripped-envelope supernovae, five of which had clumpy 3D geometry.
The findings of the research support the clumpy 3D scenario of supernovae explosions, despite the bipolar explosion scenario being the widely accepted one in the scientific community.
Convective motion in the explosions could account for this clumpy shape, according to the researchers.
The findings could become a catalyst to further understand how supernovae explosions take place.