AVAO wrote: ↑Fri Feb 23, 2024 7:12 pm
The study is very exciting.
What still irritates me is the fact that the two outer rings (outlines) already existed before the breakout 1987,
which to me indicates cyclical breakouts.
Thanks for your fantastic images, Jac! I absolutely agree that Sanduleak −69° 202, the supernova progenitor, must have undergone cyclical outbursts. The reason why the outer outlines "from the star to the supernova remnant" are completely unchanged can only mean, the way I understand it, that the explosive debris from the supernova has not yet reached "the outer limits" of the previously deposited material.
There is one more reason why we should absolutely assume that Sanduleak −69° 202 had lost mass before, and that is that it exploded as a blue supergiant. It may possible (I think!!!) that stars can explode as blue supergiants without going through the red supergiant stage. That would require, I think, that the core is so unstable that it collapses before it manages to make its outer layers expand enormously and cool prodigiously. Don't know if it is possible.
What is definitely possible for massive stars is to undergo episodes of great mass loss. Just consider
Eta Carina!
As for Sanduleak −69° 202, it exploded, as I said, as a blue supergiant. To me, that strongly suggests that the star had shed much (if not most) of is outer layers to change itself from a huge red supergiant into a smallish blue supergiant. If it shed its outer layers in a violent but non-destructive explosion, it may have become a supernova impostor prior to exploding as a supernova for real.
Wikipedia wrote:
Supernova impostors are stellar explosions that appear at first to be a supernova but do not destroy their progenitor stars. As such, they are a class of extra-powerful novae. They are also known as Type V supernovae, Eta Carinae analogs, and giant eruptions of luminous blue variables (LBV).
Supernova impostors appear as remarkably faint supernovae of spectral type IIn—which have hydrogen in their spectrum and narrow spectral lines that indicate relatively low gas speeds. These impostors exceed their pre-outburst states by several magnitudes, with typical peak absolute visual magnitudes of −11 to −14, making these outbursts as bright as the most luminous stars. The trigger mechanism of these outbursts remains unexplained, though it is thought to be caused by violating the classical Eddington luminosity limit, initiating severe mass loss. If the ratio of radiated energy to kinetic energy is near unity, as in Eta Carinae, then we might expect an ejected mass of about 0.16 solar masses.
It is not certain that Sanduleak −69° 202 has ever been a supernova impostor. But in my opinion, it is indeed highly likely that this star has shed so much mass that it turned itself into a blue instead of a red supergiant. And as I said, the debris from the supernova has not yet caught up with the matter that was shed by Sanduleak −69° 202 before it went supernova.
The Astrophysics Spectator wrote:
SN 1987A is classified as an unusual type II supernova. It is type II because it has hydrogen lines in its spectrum. It is unusual because the doppler shift of those lines suggests an expansion of around one-tenth the speed of light (twice the expansion speed of a typical type II supernova) and because it is much less luminous than a typical type II supernova, although the total amount of energy released in the explosion is similar to that released in a typical type II supernova. SN 1987A is also unusual in brightening in only 3 hours, rather than over the several days that is more typical of type II supernovae.
These unusual features are directly tied to the small radius of the exploding star. The rapid brightening of the star directly reflects this small radius; more time is required for the energy released by the collapse of a star's core to travel to the photosphere of a red supergiant than to that of a blue supergiant, because the red supergiant is physically much larger than the blue supergiant. The remaining-two characteristics?the high velocity and the low luminosity?are set by the star's radius through the thermodynamics of a supernova.
Sanduleak −69° 202 was a blue supergiant because it had shed so much of its outer layers from when it was a red supergiant. The cast-off layers still form the outer outline of the pre-supernova Sanduleak −69° 202 as well as of SN 1987A!
At least that's my take on it!
Ann
