Appearance of supernova burst

How exactly does a supernova burst look like?

I gather that in 1987, no one notived until some half a day
afterwards. They found a pair of old photos with one hour interval,
one before and one after burst. They did not hae spectra.

But what is the light curve and spectrum of a supernova like if you
happen to stare at it right when it explodes? The first minutes, first
seconds, first parts of second?

Especially funny would be the burst of a supernova of a first kind.
For a presupernova of the first kind is a white dwarf with radius of
just a few thousands km. This means that at some moment it would begin
collapsing with speeds of around 10 000 km/s. Th initial developments
of magnitude and spectrum would occur over the timescale of tenths of
second after it exceeds the Chandrasekhar limit. Ad then, the collapse
would be stopped over a few kilometres at a speed of around 100 000
km/s. This means that the luminosity would increase by orders of
magnitude ofer tens of microseconds!

I have heard that while the Crab exploded in 1054 to magnitude -4 or
-6 and is of second kind, there is supposed to have been another
supernova slightly earlier, like 1004 or 1018 or something, with
magnitude of -10 and supposedly of first kind.

How would it look? Given that the whole starlit sky has magnitude of
-5 while full moon is -12,7, the supernova would be 100 times brighter
than the rest of stars and just 10 times dimmer than the Moon. Would
the supernova have instantly cast shadows of the landscape provided it
burst at night without moonlight? And would it have produced an
instant difference in a heavily overcast night?

(Crown-Horned Snorkack) wrote in message
om:

How exactly does a supernova burst look like?

I gather that in 1987, no one notived until some half a day
afterwards. They found a pair of old photos with one hour interval,
one before and one after burst. They did not hae spectra.

But what is the light curve and spectrum of a supernova like if you
happen to stare at it right when it explodes? The first minutes, first
seconds, first parts of second?

Especially funny would be the burst of a supernova of a first kind.
For a presupernova of the first kind is a white dwarf with radius of
just a few thousands km. This means that at some moment it would begin
collapsing with speeds of around 10 000 km/s. Th initial developments
of magnitude and spectrum would occur over the timescale of tenths of
second after it exceeds the Chandrasekhar limit. Ad then, the collapse
would be stopped over a few kilometres at a speed of around 100 000
km/s. This means that the luminosity would increase by orders of
magnitude ofer tens of microseconds!

The luminosity could also increase for hours, maybe days as the hot gas
cloud expands.


I have heard that while the Crab exploded in 1054 to magnitude -4 or
-6 and is of second kind, there is supposed to have been another
supernova slightly earlier, like 1004 or 1018 or something, with
magnitude of -10 and supposedly of first kind.

How would it look? Given that the whole starlit sky has magnitude of
-5 while full moon is -12,7, the supernova would be 100 times brighter
than the rest of stars and just 10 times dimmer than the Moon. Would
the supernova have instantly cast shadows of the landscape provided it
burst at night without moonlight?

Definitely. Shadows may even be noticeable with the Moon visible, if it's
at a very different angle.

And would it have produced an
instant difference in a heavily overcast night?

Very likely, unless the Moon is visible.

In article ,
Crown-Horned Snorkack wrote:
I gather that in 1987, no one notived until some half a day
afterwards. They found a pair of old photos with one hour interval,
one before and one after burst. They did not hae spectra.

The first "observation" of SN 1987 was from neutrino counting
experiments which saw an increased flux of neutrinos some hours before
the light came out. But it would have taken a number of hours for the
shock waves from the core collapse/ explosion to propagate to the star's
surface, so the question of "when a SN explosion takes place is rather
moot. In theory, it is when the core collapses, but unless your
spacecraft has dragged along a few 10s of thousand tonnes of
dry-cleaning fluid as a neutrino detector, then the first thing you'll
see in orbit around the star is the surface going BOOM.

or a presupernova of the first kind is a white dwarf with radius of
just a few thousands km. This means that at some moment it would begin
collapsing with speeds of around 10 000 km/s.

You seem to be mixing type I and type II supernovae. Type I are
when material accumulates on the surface of a white dwarf, and then
undergoes (reasonably) conventional fusion; type II are caused by the
collapse of the core of a massive star. But this core-collapse will take
place *under* the superstructure of a star, and be effectively masked
from view for a number of hours.

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

Aidan Karley wrote:

In article ,
Crown-Horned Snorkack wrote:
I gather that in 1987, no one notived until some half a day
afterwards. They found a pair of old photos with one hour interval,
one before and one after burst. They did not hae spectra.

The first "observation" of SN 1987 was from neutrino counting
experiments which saw an increased flux of neutrinos some hours before
the light came out. But it would have taken a number of hours for the
shock waves from the core collapse/ explosion to propagate to the star's
surface, so the question of "when a SN explosion takes place is rather
moot.

Wouldn't there be a UV flash when the neutrinos break the surface ?
I can imagine circumstances where a UV flash would - partly - "spill
over" to the visible part of the spectrum.

or a presupernova of the first kind is a white dwarf with radius of
just a few thousands km. This means that at some moment it would begin
collapsing with speeds of around 10 000 km/s.

You seem to be mixing type I and type II supernovae. Type I are
when material accumulates on the surface of a white dwarf, and then
undergoes (reasonably) conventional fusion;

Right so, but the fusion is *triggered* by the collapse of the white
dwarf when it reaches the Chandrasekhar limit.
But don't ask me about the speed if the collapsing matter.

--
I recommend Macs to my friends, and Intel machines
to those whom I don't mind billing by the hour

In article , Anders Eklöf
wrote:
Right so, but the fusion is *triggered* by the collapse of the white
dwarf when it reaches the Chandrasekhar limit.

I'd have to check, but IIRC one type of type I SN is the result
of a white dwarf being taken over the Chandrasekhar limit by accretion,
but a different type is when the accretion puts sufficient fusible
matter onto the surface of the white dwarf to undergo fusion without
substantially disrupting the white dwarf itself. One is a type Ia, one
is a type Ib; I can't remember which is which.

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

Aidan Karley wrote:

I'd have to check, but IIRC one type of type I SN is the result
of a white dwarf being taken over the Chandrasekhar limit by accretion,
but a different type is when the accretion puts sufficient fusible
matter onto the surface of the white dwarf to undergo fusion without
substantially disrupting the white dwarf itself.

You better check - the latter is not a supernova, rather a regular or
recurrent nova, which is about 10 magnitudes fainter.

Eventually such a star may go supernova at a later stage if there is
enough matter to accrete, e.g. in the form an unevolved binary
companion. I've read somewhere that U Sco may be going that way.


--
I recommend Macs to my friends, and Intel machines
to those whom I don't mind billing by the hour