Two of the supernovae (PTF09atu and PTF09cnd) discovered by the Palomar Transient Factory. Left: before explosion. Right: after explosion.
Credit: Caltech/Robert Quimby/Nature
PARIS: Astronomers have reported that six ultra-bright flashes detected in deep space were ancient exploding stars that are a new kind of supernova.
Among the most luminous in the cosmos, these new kinds of supernovae could help researchers better understand star formation, distant galaxies, and what the early universe might have been like.
"We have a whole new class of objects that can't be explained by any of the models we've seen before," said Robert Quimby of the California Institute of Technology (Caltech) who led the probe into the strange explosions. The study appears in the current issue of Nature.
No known chemical signatures
Most supernovae occur when a very massive star runs out of fuel, its core collapses and then explodes, leaving behind a neutron star or a black hole.
There is also a rarer kind in which mass flows from a cooling ageing star called a red star to a ‘white dwarf’, the hot and dense core of an old star, which eventually collapses in on itself and then explodes.
But six supernovae observed by Quimby and his team had none of the chemical signatures of these known supernovae.
100 billion times brighter than Sun
Quimby first made headlines in 2005 when - as a graduate student at the University of Texas, Austin - he discovered what was then the brightest supernova ever found: 100 billion times brighter than the Sun and 10 times brighter than most other supernovae.
Dubbed 2005ap, it was also a little odd. For one thing, its spectrum - the chemical fingerprint that tells astronomers what the supernova is made of, how far away it is, and what happened when it blew up - was unlike any seen before. It also showed no signs of hydrogen, which is commonly found in most supernovae.
At around the same time, astronomers using the Hubble Space Telescope discovered a mysterious supernova called SCP 06F6. This supernova also had an odd spectrum, though there was nothing that indicated this cosmic blast was similar to 2005ap.
That sparked the formation of a special team called the Palomar Transient Factory to scan the skies for ‘transients’, as ephemeral flashes are called, but combining the optical power of hefty telescopes in California, Hawaii and the Canary Islands.
A perfect match
Quimby realised that if you slightly shifted the spectrum of 2005ap, it looked a lot like these four new objects. The team then plotted all the spectra together. "Boom -it was a perfect match," he recalled.
According to Quimby, the two mysterious supernovae - 2005ap and SCP 06F6 - had looked different from one another because 2005ap was 3 billion light-years away while SCP 06F6 was 8 billion light-years away.
More distant supernovae have a stronger cosmological redshift, a phenomenon in which the expanding universe stretches the wavelength of the emitted light, shifting supernovae spectra toward the red end.
