A 2.7 billion light-years, a giant galaxy with several hundred billion stars shining in the cosmos left. This picture was taken in 2014. On the right, in June 2015, a supernova of extraordinary brilliance eclipse by its glow the entire galaxy … Photos ASAS-SN.
Each day across the visible Universe , a distance of 13 billion light-years, and in one of a hundred billion galaxies in this space-time volume three millions of stars disappear in a gigantic explosion, a supernova …
Reduced to a more human scale cosmic , a large galaxy such as our own, the Milky Way, has one or two explosions per century . Supernova … Behind this generic term hides two, at least, stellar phenomena totally different.
Supernovae Type II are the simplest to understand : very massive stars, once all of their spent nuclear fuel, unable to burn the iron they have created in their nuclear forge, abruptly collapsing on them yourself, before exploding and sow the cosmos valuable elements they have synthesized: carbon, oxygen, magnesium, silicon, etc … Without supernovae, we would not exist, nor the water of our rivers, or gold in our jewelry, nor the planet welcomes us
Type I supernovae are different . the explosion takes place in an old pair of stars. The first is a white dwarf, a former star, devoid of nuclear reactions, which turns off gradually. The second is a red giant, an old Sun on the verge of extinction and in turn become a white dwarf. In these tight pairs, the white dwarf starts to absorb the material of its giant neighbor, until the white dwarf collapses on itself, creating a gigantic thermonuclear explosion, in which it is completely destroyed.
> These stars are quite well known: amateur and professional astronomers are discovering every day or almost
Their luster is extraordinary , since they shine on average. like a billion suns … But
supernova discovered in June 2015 in a galaxy is completely, radically different … So for now it thwarts the calculations of specialists of stellar evolution. Clearly, the star, called ASASSN-15lh, is too much too bright …
The star was discovered June 14, 2015 at the Cerro Tololo Observatory , Chile by the ASAS-SN monitoring network. This sky monitoring network consists of simple telephoto focal length of 400 mm equipped with CCD cameras and pointing systems, and automated data transmission. Material within the reach of an amateur astronomer.
Except … When the international team of Subo Dong has found the “new star” in the data transmitted by ASAS-SN and measured the distance, what a surprise! The ASASSN 15lh-supernova was located 2.7 billion light-years. To be observed with a small telescope at such a distance, the explosion would be of incredible power …
And indeed, this is the case. ASASSN-15lh, when its maximum brightness, shining more than 500 billion suns … An extraordinary figure, never seen: the supernova brightness exceeds any that have been discovered so far
Theorists do not know how to explain. such a burst of energy , and the mystery is likely to remain around the supernova, too far, and now goes out gradually being difficult to study and analyze. The researchers hope now is that such an event, sometimes called hypernova happens again near us. Closer, but not too close anyway …
Indeed, try to imagine such a star . Astronomers say that its absolute magnitude – its intrinsic brightness – was -23.5. This is about a thousand times more than the supernovae “normal”
This means that if it had exploded in our own galaxy , this supernova would have profoundly changed humanity. To fifteen thousand years -light, an enormous distance, our galaxy, the star would have shone like a neighborhood Moon … A 5000 light years, dazzling as the Full Moon, the supernova would have illuminated the night landscapes … a hundred light-years, the sky night was blue, without any visible star, and punctual and metallic luster, the supernova would have been unsustainable. Ten light-years, ie the distance of the closest stars is a second sun, blinding, which would have shone in the sky and would have completely unbalanced the earth’s climate, threatening most animal species and probably also the human species, as the invisible flow of UV, X and gamma would have been devastating.
Does cosmic plane Such risk on our planet? In theory, yes This is possible, in practice, no. There are no supergiant star close to the Earth, and statistically, astronomers believe these “hypernovae” are very rare: he must explode in the Milky Way one every million years …
Serge Brunier
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