Supernovae are the superstars of celestial bestiary. As luminous as hundred billion stars, these spectacular star explosions are useful for us to probe the mysteries of dark energy. An international group astronomers has just discovered one of them having exploded 11 billion years ago. It is so far the most distant observed.

There are two main types of supernovae in which we define the subdivisions. A supernova type SN I is normally the result of the thermonuclear explosion of a white dwarf accretion of matter from its companion star, the two stars forming a binary system. The power of the explosion varies little and does not detect characteristic lines of hydrogen but rather those caused by heavy elements like carbon and oxygen (SN I may arise from the collision of white dwarfs).

In fact, only the SN I are the product of an explosion of white dwarfs, SN Ib and SN Ic are special cases because they are close cousins of SN II.

SN II supernovae are the origin of stars at least 8 times more massive than our Sun. They burn their nuclear fuel much faster than the Sun and it is in their heart that heavy elements such as sulfur and iron can be synthesized. Unstable, they end their lives exploding and scattering the elements they produced in interstellar space, which can be used to make planets like ours or complex organic molecules. The spectrum of light emitted by a SN II shows the presence of hydrogen and helium but when the upper layers of the stars have been blown before its explosion, for one reason or another, it will appear as a SN Ib or SN Ic.

Stacking images to identify the Faint stars:

The supernova which was discovered by Jeff Cooke and his colleagues are Type II supernovae. They are characterized by brightness lasting longer and narrower lines of hydrogen. This kind of supernovae is very likely to occur where massive star explodes in an environment rich in dense gas. It is the early impact of matter ejected by the explosion and the gas explosion which slows and causes the illumination of the latter on the passage of the shock wave.

The supernovas of Cooke are not characterized only by their nature. They are exceptional in their distance. One occurred about 6 billion years ago and the other occurred about 11 billion years ago. This makes them the most distant supernovae known in the observable Universe, aged 13.7 billion years.

The discovery was not made by chance. Astronomers had been hunting on SN II. Their powerful ultraviolet emissions, their luminosity more important and lasting longer than the usual SN II could give them a chance to observe them despite large distances and the influence of redshift. With these supernovae  we can estimate the rate of formation of massive stars when the Universe was still young.

The technique used initially consisted in piling up photographs of the remote Universe taken at different times. It’s the equivalent of a long pose done with a camera to collect the maximum of photons from a few bright object. The researchers had to only check then, by a spectral study carried out with the helps of the Canada-France-Hawaii telescope located on Mauna Kea.