[mysterypie]

It's nice that the nuclear explosion of novas and supernovas occur on a human perceptible timescale -- taking weeks to months, instead of a nanosecond or ten million years. I'm not suggesting anything superstitious or supernatural about it. Just that it's oddly convenient.

[teraflop]

The speed of light pretty much precludes anything happening to an entire star on a nanosecond timescale.

In the other direction, it's basically a tautology. A "nova" or "new star" is, by definition, a relatively fast change. Much slower changes to stars also occur, but they tend not to get news articles written about them when they happen gradually over millions of years, and we don't call them novas.

[dredmorbius]

For a main-sequence star, yes.

For a neutron star, at ~12 -- 30 km diameter, light-speed timescales are on the order of 40--100 microseconds, which would be the lower bound on whole-star cataclysmic events.

(Time dilation might extend this somewhat, perhaps by a factor of two or so.)

For a white dwarf, ~10,000 km, lightspeed events would be about 30 milliseconds (~300 times longer than on the neutron star). That's about 1/10 of an eyeblink.

[teekert]

I’m not religious but my fav “that’s oddly convenient“ fact is that just by going fast enough you can cross the universe in a human lifetime because of time slowing down. As a biologist I find that much more fascinating than all those poor “irreducible complexity” anti-evolution arguments. Perhaps a physicist feels the other way around.

[Arnavion]

Well, you can cross the universe in any amount of time. The human lifetime isn't special in that regard. A photon crosses the universe in zero time, and anything with non-zero mass can get arbitrarily close to zero time.

[dredmorbius]

As I've seen this point made in the past, it's that travelling at a constant 1g acceleration the subjective time for an astronaut would be about 45 years in traversing the observable Universe (~14 billion light years).

That is, a comfortable and familiar acceleration gives a human-lifetime-equivalent journey (subjective time).

If you're planning a round-trip, you'll find rather more time has transpired on what used to be Earth.

<https://www.universetoday.com/129086/far-can-travel/>

[saalweachter]

> If you're planning a round-trip, you'll find rather more time has transpired on what used to be Earth.

Or less, depending on the rotation of the universe as a whole.

[ben_w]

Or no return may be possible at any speed/acceleration given the expansion of the universe.

[dredmorbius]

Given that the outbound journey is already technically challenging, that's very nearly quibbling, despite cosmological accuracy.

[heavenlyblue]

That 1g constant acceleration requires practically infinite amounts of energy

[dredmorbius]

True.

However it is also the specific context in which the lifetime-universe-traversal concept emerges.

[denton-scratch]

> A photon crosses the universe in zero time

That is not consistent with my observations.

[Intralexical]

Multiple universes, perhaps, depending on your cosmology/eschatology:

https://en.wikipedia.org/wiki/Tau_Zero

[sweezyjeezy]

Example: the Crab Nebula was the result of a supernova that was seen by Chinese astronomers about 1000 years ago: https://en.wikipedia.org/wiki/Crab_Nebula

[yitchelle]

Surely these are occurring very frequently as there are trillions of stars out there. I imagine that space is so vast that the vastness makes these events difficult to observe. Am I wrong with this thought?

[NohatCoder]

It is only 2600 light years away. Our galaxy is a little under 100000 light years across, depending on how you measure. So it is a rare type of double star, and it is very close to Earth, the combination is what makes it special.

[widforss]

> This recurring nova is only one of five in our galaxy.

[SiempreViernes]

Just like how you can't see much of your body (without mirrors) because your body is in the way, we can't see much of the galaxy because there's galaxy in the way.

[kugelblitz]

> This could be a once-in-a-lifetime viewing opportunity as the nova ouburst [sic] only occurs about every 80 years.