Astronomers using European Southern Observatory’s (ESO) Very Large Telescope (VLT) have for the first time obtained a three-dimensional view of the distribution of the innermost material expelled by a recently exploded star.
The original blast was not only powerful, according to the new results. It was also more concentrated in one particular direction.
This is a strong indication that the supernova must have been very turbulent, supporting the most recent computer models.
Unlike the Sun, which will die rather quietly, massive stars arriving at the end of their brief life explode as supernovae, hurling out a vast quantity of material.
In this class, Supernova 1987A (SN 1987A) in the nearby Large Magellanic Cloud galaxy occupies a very special place. Seen in 1987, it was the first supernova for 383 years bright enough to be seen in the sky with just the naked eye.
Because of its relative closeness, it has been possible for astronomers to study the explosion of a massive star and its aftermath in more detail than ever before.
SN 1987A has been a bonanza for astrophysicists. It provided several notable observational ‘firsts’: the detection of neutrinos from the collapsing inner stellar core triggering the explosion; the identification on archival photographic plates of the star before it exploded; the signs of a lopsided explosion; the direct observation of the radioactive elements produced during the blast; observation of the formation of dust in the supernova, as well as the detection of the gas surrounding the star.
A lopsided blast
New observations making use of a unique instrument, SINFONI, on the VLT have provided even deeper knowledge of this amazing event, as astronomers have now been able to make the first-ever 3D reconstruction of the central parts of the exploding material.
This view shows that the explosion was stronger and faster in some directions than others, leading to an irregular shape with some parts stretching out further into space.
The first material to be ejected from the explosion travelled at an incredible 100 million km per hour, which is about a tenth of the speed of light or around 100,000 times faster than a passenger jet.
Even at this breakneck speed it has taken the blast 10 years to reach a previously existing ring of gas and dust puffed out much earlier from the dying star. The images also demonstrate that another blast wave is travelling ten times more slowly and is being heated by radioactive elements created in the explosion.
“We have established the velocity distribution of the inner ejecta of Supernova 1987A,” says lead author Karina Kjær. “Just how a supernova explodes is not very well understood, but the way the star exploded is imprinted on this inner material. We can see that this material was not ejected symmetrically in all directions, but rather seems to have had a preferred direction. Besides, this direction is different to what was expected from the position of the ring.”
Such asymmetric behaviour was predicted by some of the most recent computer models of supernovae, which found that large-scale instabilities occur during the explosion. The new observations are thus the first direct confirmation of such models.
Adapted from information issued by ESO / L. Calçada.
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