# How quickly does a supernova heat up/expand?

Suppose there's a star out there that's a lot more massive than the Sun.

Suppose further that orbiting this star is a planet not unlike Earth. Water, oxygen, civilization, and all.

Now the star decides to go supernova. How quick, or slow, is the process?

How long will it take it to heat up to make life on that planet impossible? A month? A year? A hundred years? A thousand years?

And how long will it take for the supernova to engulf the planet? A day? A month? A year? A million years?

• It is worth noting that if the star is more massive than the earth, big enough to go supernova, then it doesn't live for very long, not long enough for civilisation to have developed. Also it would be at the end of its life, so would have expanded into a red giant (or may be pulsing through luminous blue variable stage) either way, it will have become even more powerful than it was when younger, and would have already have torched any planets that may have been in its habitable zone. Dec 18 '15 at 22:27
• @JamesKilfiger: Thank you. Hmm. Civilization as we know it develops in a blink by astronomical standards. Doesn't it? What's a few thousand years. Dec 19 '15 at 0:00
• @JamesKilfiger So we infer that the civilisation did not originate there... Dec 19 '15 at 0:18
• It only took 1000,000 years for stone-tool making apes to form civillisations (and then only a few thousand to develop the means to destroy themselves). But it took nearly 4 billion years for self-replicating strands of DNA to evolve stone-tool making apes. A large star shines for as little as 10 million years before going supernova, and the red giant phase for much less than that. A colony of space-faring aliens could have been built on a planet orbiting a star that is a potential supernova precursor, but not a native civilisation. They would find the planet a pretty hostile place. Dec 19 '15 at 9:31

The supernova continues to become more luminous for about a week thereafter, increasing in luminosity, from what must have already been enormous (thousands of solar luminosities) by another factor of $10^5$. The equilibrium temperature of any planet scales roughly as $L^{1/4}$, so temperatures would rise by more than an order of magnitude in a week.