New insights about the brightest explosions in the Universe

January 23, 2020

Swedish and Japanese researchers have, after ten years, found an explanation to the peculiar emission lines seen in one of the brightest supernovae ever observed - SN 2006gy. At the same time they found an explanation for how the supernova arose.

Superluminous supernovae are the most luminous explosions in cosmos. SN 2006gy is one of the most studied such events, but researchers have been uncertain about its origin. Astrophysicists at Stockholm University have, together with Japanese colleagues, now discovered large amounts of iron in the supernova through spectral lines that have never previously been seen either in supernovae or in other astrophysical objects. That has led to a new explanation for how the supernova arose.

"No-one had tested to compare spectra from neutral iron, i.e. iron which all electrons retained, with the unidentified emission lines in SN 2006gy, because iron is normally ionized (one or more electrons removed). We tried it and saw with excitement how line after line lined up just as in the observed spectrum", says Anders Jerkstrand, Department of Astronomy, Stockholm University.

"It became even more exciting when it quickly turned out that very large amounts of iron was needed to make the lines - at least a third of the Sun's mass - which directly ruled out some old scenarios and instead revealed a new one."

The progenitor to SN 2006gy was, according to the new model, a double star consisting of a white dwarf of the same size as the Earth and a hydrogen-rich massive star as large as our solar system in close orbit. As the hydrogen rich star expanded its envelope, which happens when new fuel is ignited in the late stages of evolution, the white dwarf was caught in the envelope and spiralled in towards the centre of the companion. When it reached the centre the unstable white dwarf exploded and a so-called Type Ia supernova was born. This supernova then collided with the ejected envelope, which is flung out during the inspiral, and this gigantic collision gave rise to the light of SN 2006gy.

"That a Type Ia supernova appears to be behind SN 2006gy turns upside down what most researchers have believed", says Anders Jerkstrand.

"That a white dwarf can be in close orbit with a massive hydrogen-rich star, and quickly explode upon falling to the centre, gives important new information for the theory of double star evolution and the conditions necessary for a white dwarf to explode."

Fact: Superluminous supernovae

Superluminous supernovae are the brightest explosions in the Universe. Over a few months they radiate as much energy as the Sun does over its whole lifetime and reach a peak brightness as high as that of an entire galaxy. The origin of this energy, and what kind of star system that has exploded, are still unclear and debated.

Fact: Emission line

An emission line is a bright feature in the spectrum of a light source. The lines arise as each element in the source emit light at specific wavelengths, and from this one can see which elements are present in the source. Examples of emission line sources are certain astrophysical objects.
The article

"A Type Ia supernova at the heart of superluminous transient SN 2006gy" is published in Science 24 January. Doi: 10.1126/science.aaw1469


Anders Jerkstrand, Department of Astronomy, Stockholm University. E-mail:

Stockholm University

Related Supernova Articles from Brightsurf:

Scientists discover supernova that outshines all others
A supernova at least twice as bright and energetic, and likely much more massive than any yet recorded has been identified by an international team of astronomers, led by the University of Birmingham.

Supernova observation first of its kind using NASA satellite
Their research, detailed in the Monthly Notices of the Royal Astronomical Society, represents the first published findings about a supernova observed using TESS, and add new insights to long-held theories about the elements left behind after a white dwarf star explodes into a supernova.

Astronomers find possible elusive star behind supernova
Astronomers may have finally found a doomed star that seemed to have avoided detection before its explosive death.

Stellar thief is the surviving companion to a supernova
Hubble found the most compelling evidence that some supernovas originate in double-star systems.

Supernova may have 'burped' before exploding
Only by increasing the rate at which telescopes monitor the sky has it been possible to catch more Fast-Evolving Luminous Transients (FELTs) and begin to understand them.

An unusual white dwarf may be a supernova leftover
Astronomers have identified a white dwarf star in our galaxy that may be the leftover remains of a recently discovered type of supernova.

Researchers show how to make your own supernova
Researchers from the University of Oxford are using the largest, most intense lasers on the planet, to for the first time, show the general public how to recreate the effects of supernovae, in a laboratory.

The big star that couldn't become a supernova
For the first time in history, astronomers have been able to watch as a dying star was reborn as a black hole.

Seeing quadruple: Four images of the same supernova, a rare find
Galaxies bend light through an effect called gravitational lensing that helps astronomers peer deeper into the cosmos.

Explosive material: The making of a supernova
Pre-supernova stars may show signs of instability for months before the big explosion

Read More: Supernova News and Supernova Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to