Thursday, January 16, 2014

Supernova Sheds New Light on an Old Astrophysical Mystery

Optical spectra of the broad-lined Type Ic SN 2012ap during its first ~40 days after explosion.   Three prominent DIBs around 4428 A, 5780 A, and 6283 A are highlighted with dashed lines.

For close to a century astronomers that work with spectroscopy of stars at optical and near infrared wavelengths have struggled to understand small absorption features called the diffuse interstellar bands (DIBs). Over 400 features are presently known that regularly appear in and contaminate data. Enigmatically, however, the origin of DIBs have remained unknown despite exhaustive experimental, theoretical, and observational studies.

It's an embarrassment in astronomy that these absorptions -- which are thought to be carbon-rich molecules associated with a large reservoir of the universe's organic material -- cannot be confidently associated with any known atomic or molecular lines.

A new paper led by Dan Milisavljevic of the Harvard-Smithsonian Center for Astrophysics uses the light of an exploding star to investigate the mysterious DIBs. He and collaborators detected unusually strong DIBs in the optical spectra of an energetic supernova explosion named SN 2012a that changed over time. They attributed the changes to interaction between the supernova and the source of the DIBs

The Southern African Large Telescope (SALT) played a key role in this discovery. An ongoing program led by Robert Fesen at Dartmouth College was triggered to monitor the supernova in its early stages of evolution and obtain data of sufficient resolution to detect the DIBs. Additional supporting observations presented in the paper came from Harvard and Caltech facilities.

The presence of DIB features provides information about the much speculated progenitor stars behind the explosions, and the fact that the changes in the absorption strength of the various DIBs were not uniform provides important clues about the location and physical traits of the source material.

Supernova observations are typically made with low resolutions to maximize signal strength and wavelength coverage. However, Milisavljevic's work has demonstrated that this practice may not be good enough. Supernova light may be regularly transmitting a wealth of detailed information long overlooked because astronomers haven't been wearing glasses with a prescription strong enough to read them.

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