How The Brightest Supernovae Become Superluminous

Artist's impression of a superluminous supernova producing shockwaves in a surrounding gas cloud. Kavli IMPU

Supernovae are some of the brightest events in the universe, and some of them are so bright they get their own class. These superluminous supernovae (SLSNe) have long puzzled scientists, but now an international group of astronomers think they have worked out their origins.

Using sophisticated computer simulations, the team worked out that SLSNe that lack hydrogen are surrounded by dense clouds of carbon and oxygen. When the stars actually explode, these clouds are lit up by the shockwaves of the supernova, producing the increased luminosity that we observe. A study describing the findings is published in the Astrophysical Journal.

Supernovae usually become a billion times brighter than the star they used to be and then they glow for a few weeks before dimming again. These SLSNe can be between 10 and 100 times more luminous than a regular supernova, and they remain brighter for longer.

The study looked at the case of two specific SLSNe called SN 2010gx and PTF09cnd. In both cases, the star is believed to be surrounded by a dense nearby cloud made from ejected material.

Stars at the end of their life tend to eject a significant amount of mass but even when that is taken into account, these objects clearly seemed to be extreme events. 

To create the model and reproduce SN 2010gx, astronomers expected a cloud of material that has a mass between five and 10 times the mass of our Sun. If that sounds impressive, then PTF09cnd will (literally) blow you away. The supernova must have been surrounded by a cloud of 55 suns worth of material.

While the research is impressive, this is just a first approach in solving the mystery of these incredibly bright events. The simulation simplifies the problem significantly, and there might be some subtleties in the turbulent moves of the material that is currently missing from the explanation.

Another issue is that, according to the most likely model, these stars are not only hydrogen-poor but also helium poor. Stellar evolution theories argue strongly against a star that has lost all its helium. The team implemented different approaches to include helium in the fold, but so far they don’t work as well.

The team argued that future observations should hopefully provide enough information about helium composition to help refine the models and expand what we know about superluminous supernovae.   

[H/T: Kavli IPMU]

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