Supernovae are the explosive deaths of massive stars. Among the most momentous events in the cosmos, they disburse into space all of the chemical elements that were produced inside their progenitor stars, including most of the elements essential for making planets and life. Astronomers have recognized for decades that there are several different kinds of supernovae, most fundamentally those that originate from a single massive star and those that develop when one member of a pair of binary stars becomes massive by feeding on its neighbor. Other factors like the stellar composition also come into account. Sorting out all these various complications is critical if astronomers want to be able to reliably classify any particular supernovae and thereby infer its intrinsic brightness, and then use its observed brightness as a measure of its distance.
Recent wide-field surveys searching for supernovae have found that the conventional schema for classifying supernovae may be even more complicated than previously thought. A few years ago a new class called superluminous supernovae was found, characterized by their emitting total radiated energies equal to about ten billion suns shining for a year. Some of these new objects were discovered at cosmological distances, helping to cement the notion that new types were being discovered, and further studies have found even more subdivisions, also based among other things on composition. These new superluminous supernovae can be identified and characterized by the particular way their light fades away after the brightness peak, driven in part by the radioactive decay of elements manufactured in the explosions.
CfA astronomers Ryan Chornock, Edo Berger, Ryan Foley, Chris Stubbs and Maria Drout and a team of their colleagues studied a superluminous supernova spotted in December 2010. They followed it for the next year, obtaining spectra that place the object so distant that its light has been traveling for about six billion years, placing it at an intermediate cosmic distance (and epoch) between the local and cosmologically distant, early universe. Their analysis finds that this object belongs to the new class of superluminous supernovae, but they also find that some of its features (for example, the lack of strong iron emission) point to an even more complex story at work than previously suspected. They speculate that the explosion left behind a spinning neutron star -- a super-dense residue (composed of neutrons) with the mass of the Sun within a diameter of about ten miles -- and that the spinning object is also highly magnetized. As the stellar spin slows down, magnetic field effects help to keep the source shining brightly.
"The Superluminous Supernova PS1-11ap: Bridging the Gap between Low and High Redshift," M. McCrum, S. J. Smartt, R. Kotak, A. Rest, A. Jerkstrand, C. Inserra, S. A. Rodney, T.-W. Chen, D. A. Howell, M. E. Huber, A. Pastorello, J. L. Tonry, F. Bresolin, R.-P. Kudritzki, R. Chornock, E. Berger, K. Smith, M. T. Botticella, R. J. Foley, M. Fraser, D. Milisavljevic, M. Nicholl, A. G. Riess, C. W. Stubbs, S. Valenti, W. M. Wood-Vasey, D. Wright, D. R. Young, M. Drout, I. Czekala, W. S. Burgett, K. C. Chambers, P. Draper, H. Flewelling, K. W. Hodapp, N. Kaiser, E. A. Magnier, N. Metcalfe, P. A. Price, W. Sweeney and R. J. Wainscoat, MNRAS 437, 6556, 2013.