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Alpha Centauri is 4.3 light years away. If it exploded suddenly, would we be able to know this in advance? As the light from the supernova will not reach us before 4.3 years.

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  • $\begingroup$ "As the light from super Novae will not reach us before 4.3 years." do you know of another way of getting information from the cosmos $\endgroup$
    – anna v
    Feb 9 '20 at 9:35
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    $\begingroup$ Suggestion: Replace Alpha Centauri with a star that actually could go supernova. $\endgroup$
    – Qmechanic
    Feb 9 '20 at 11:08
  • $\begingroup$ in a similar situation you would have even less warning that our sun had disappeared eight minutes earlier. $\endgroup$ Feb 9 '20 at 18:06
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Yes, you would get a few hours warning from the intense pulse of gravitational waves and neutrinos caused by the core collapse. Incidentally, I should say that this does not actually apply to Alpha Cen, since this is a solar-type star that will never produce a supernova.

The gravitational waves and neutrinos also travel at the speed of light (well, almost in the case of neutrinos), but they can escape promptly (within a few seconds) of the core collapse, whereas the "fireball" that produces the electromagnetic signature takes several hours to work its way to the surface of the star.

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  • $\begingroup$ Sorry to always ask via comments but sometimes is even more natural. Is it a similar mechanism that might alert astronomers about impelling gamma rays burst? I guess so. That I don't know exactly why the burst emerge is another story and I should search or pose a separate question about this... $\endgroup$
    – Alchimista
    Feb 9 '20 at 13:20
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    $\begingroup$ @Alchimista it depends what kind of gamma ray burst. If it were from an exploding, rapidly rotating supergiant, then yes (though great distances would mean no neutrino burst would be observable and probably no GWs either). Gamma Rays from merging neutron stars are released promptly (e.g. 2s delay between GWs and gamma rays for the recent kilonova detected as a GW source). $\endgroup$
    – ProfRob
    Feb 9 '20 at 13:31
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No information can travel faster than the speed of light in a vacuum. Gravity also travels at this speed. So if Alpha Centaury had any change 4 years ago we would have no way of knowing it for about another 0.37 years. We see it and feel any gravitational effects from it as it was about 4.37 years ago. About 4.37 years after events happened at Alpha Centauri, we would receive the information as it occured in the past.

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