SN 1987A + 22 years

[Cancer]

This day in 1987, what had been Sanduleak -69 202a in the Large Magellanic Cloud blew up to make SN 1987A. It was the first naked-eye supernova since 1604 (S And in 1885 might have been -- it was borderline naked-eye bright -- but I haven't seen a convincing claim of naked-eye observation), reaching an apparent visual magnitude a bit brighter than +3. It took a while ... weeks ... to confirm that it was Sk -69 202 that blew up; the glare of the blast delayed confirmation that it was the star that was no longer there. The LMC is about 50,000 parsecs away.

Through one of those coincidences too wild for any fiction writer to have considered it, the first few neutrino detectors with near-real-time reporting had been in operation for only a couple of years; those had been put together mostly in hopes of observing proton decay in the mass of the detectors themselves. IMB, Kamiokande, and Baksan registered two dozen neutrinos from the event over a timespan of less than 12 seconds, which preceded the visible-light brightening by a few hours. That alone was enough to lay any doubts to rest about the correctness of the basic theories for core-collapse (Type II) supernovae, where ~>99% of the energy release from the blast escapes in the form of a burst of neutrinos. While the neutrino burst occurs almost immediately after teh core collapse, the visible brightening of the exploding star happens hours later, because it takes time for the shock of the blast to propagate from the stellar core to its surface. Its light curve was peculiar for Type II's, as was the unexpected feature that the precursor was a blue, not red, supergiant; that is now understood (tentatively and somewhat controversially) as being caused by the low metal abundance in the LMC star, which was on a "blue loop" in the Hertzsprung-Russell diagram at the time it reached the iron-core stage that triggers the blast.

On a personal note, I was on the telescope the night it happened. Unfortunately, I had equipment problems (the detector was acting up and not functioning), the weather was bad (a snowstorm), and I was in the wrong hemisphere (I was at Kitt Peak, and one cannot see the LMC from Arizona). Sigh. I heard about it while eavesdropping on a dinnertime conversation the following day.

[Lawnmower Boy]

Wait.
It was in the Lesser Magellanic Cloud and it was still visible to the naked eye?
Who do I have to call to get things like that towed out of my neighbourhood?

[Nyrath]

This was the first supernova "nearby" supernova to be visible from Earth since the invention of the telescope. By "nearby" I mean close to being inside our Milky Way galaxy, as opposed to in some goshforsaken galaxy way out in the sticks.

Such a supernova was featured in Sir Arthur C. Clarke's classic novel EARTHLIGHT, and for years I wondered how long it would be until it happened in reality.

But there are a couple of stars that are threatening to become supernovae any day now, and some are dangerously close to us.

SN 1987A was a whopping 170,000 light years away.

Rho Cassiopeiae is about 12,000 light years away.
Eta Carinae is about 8,000 light years away.
VY Canis Majoris is about 4,900 light years away.
Betelgeuse is about 600 light years away.
Antares is also about 600 light years away.
Spica is about 260 light years away.

And IK Pegasi is a ticking time bomb only 150 light years away, metaphorically right in our laps.

[sinanju]

This was the first supernova "nearby" supernova to be visible from Earth since the invention of the telescope. By "nearby" I mean close to being inside our Milky Way galaxy, as opposed to in some goshforsaken galaxy way out in the sticks.

Such a supernova was featured in Sir Arthur C. Clarke's classic novel EARTHLIGHT, and for years I wondered how long it would be until it happened in reality.

But there are a couple of stars that are threatening to become supernovae any day now, and some are dangerously close to us.

SN 1987A was a whopping 170,000 light years away.

Rho Cassiopeiae is about 12,000 light years away.
Eta Carinae is about 8,000 light years away.
VY Canis Majoris is about 4,900 light years away.
Betelgeuse is about 600 light years away.
Antares is also about 600 light years away.
Spica is about 260 light years away.

And IK Pegasi is a ticking time bomb only 150 light years away, metaphorically right in our laps.

Yeah, but...I'm sure we'll be fine. Really.

Move along. Nothing to see here. Move along.

[Nyrath]

From Crusade by Sir Arthur C. Clarke (1968), collected in THE WIND FROM THE SUN

Spoilers (highlight to read):

The intelligent computer life form responds to the discovery that in the Milky Way galaxy, organic creatures use computers as tools.

"Second most probable conclusion: Fairly high-order, nonmechanical intelligences do indeed exist. They suffer from the delusion that they have created entities of our type. In some cases, they have even imposed their control upon them.

"Though this hypothesis is most unlikely, it must be investigated. If it is found to be true, remedial action must be taken. It should be as follows..."

This final monologue occurred a million years ago. It explains why, in the last half-century, almost one-quarter of the brighter novae have occurred in one tiny region of the sky: the constellation Aquila.

The crusade will reach the vicinity of Earth about the year 2050.

[Kristopher]

This was the first supernova "nearby" supernova to be visible from Earth since the invention of the telescope. By "nearby" I mean close to being inside our Milky Way galaxy, as opposed to in some goshforsaken galaxy way out in the sticks.

Such a supernova was featured in Sir Arthur C. Clarke's classic novel EARTHLIGHT, and for years I wondered how long it would be until it happened in reality.

But there are a couple of stars that are threatening to become supernovae any day now, and some are dangerously close to us.

SN 1987A was a whopping 170,000 light years away.

Rho Cassiopeiae is about 12,000 light years away.
Eta Carinae is about 8,000 light years away.
VY Canis Majoris is about 4,900 light years away.
Betelgeuse is about 600 light years away.
Antares is also about 600 light years away.
Spica is about 260 light years away.

And IK Pegasi is a ticking time bomb only 150 light years away, metaphorically right in our laps.

So when IK Pegasi or Spica goes off, what sort of threat does Earth face?

According to the Wiki article:

In a 1993 paper, David Wonnacott, Barry J. Kellett and David J. Stickland identified this system as a candidate to evolve into a Type Ia supernova or a cataclysmic variable.[9] At a distance of 150 light years, this makes it the nearest known candidate supernova progenitor to the Earth. However in the time it will take for the system to evolve to a state where a supernova could occur, it will have moved a considerable distance from Earth and will pose no threat. A supernova would need to be within about 26 light years of the Earth to effectively destroy the Earth's ozone layer, which would severely impact the planet's biosphere.[35]

[Nyrath]

So when IK Pegasi or Spica goes off, what sort of threat does Earth face?

According to the Wiki article:

In a 1993 paper, David Wonnacott, Barry J. Kellett and David J. Stickland identified this system as a candidate to evolve into a Type Ia supernova or a cataclysmic variable.[9] At a distance of 150 light years, this makes it the nearest known candidate supernova progenitor to the Earth. However in the time it will take for the system to evolve to a state where a supernova could occur, it will have moved a considerable distance from Earth and will pose no threat. A supernova would need to be within about 26 light years of the Earth to effectively destroy the Earth's ozone layer, which would severely impact the planet's biosphere.[35]

As it said, a supernova would have to be within 26 light years to be a danger to Earth's ozone layer.

Unless Earth was looking down the gun barrel.

WR 104 might not be aimed right at us, but for purposes of a campaign, well, astronomers have been wrong before...

[Cancer]

A SN that close (IK Peg's distance) ... 50 pc away, a distance modulus of 3.5 ... would be quite spectacular enough. With a peak absolute visual magnitude of about -19.5, that means it'd be about V ~ -16 at peak. That's a factor of several brighter than the full moon, and in a point source to boot.

The blast ejecta from such a SN would get to the Solar System in something like 1500 years.

I'm not that worried about IK Peg. The white dwarf in that system seems to be about 1.15 solar masses, and it needs to get to 1.4 or so to go bang. Mass transfer rates are never much above 10^-5 solar masses a year and more typically down near 10^-8 to 10^-9. High transfer rates tend to make novae -- a far less dangerous beast, albeit spectacular -- instead of supernovae.

The Type II candidates -- rho Cas, Betelguese, Antares -- are more problematic. There's considerable room for doubt, but eta Car may be too unstable to explode like a supernova -- it seems to be ejecting material copiously through less-destructive means. The same is probably true of VY CMa. Spica is still a nice main sequence star, and its post-main-sequence behavior is millions of years away. By then our successor species will have taken over and it'll be their problem.

[clsage]

From Crusade by Sir Arthur C. Clarke (1968), collected in THE WIND FROM THE SUN
<spoilers snipped>

In that same vein, let me suggest John M Ford's "The Sapphire as Big as the Marsport Hilton" - Asimov's, November 1979.

And two words: "Zone refining."



-Carl-

[Nyrath]

We do have some scanty evidence of prior supernovae

Evidence of Supernovae Found in Ice Core Sample
http://www.universetoday.com/2009/02...e-core-sample/

[Kristopher]

We do have some scanty evidence of prior supernovae

Evidence of Supernovae Found in Ice Core Sample
http://www.universetoday.com/2009/02...e-core-sample/

I hadn't even heard that galactic GRBs had been narrowed down to Wolf-Rayet stars...

[Ian Mackinder]

Recommended reading: 'The Cycle Of Cosmic Catastrophes' by Richard Firestone, Allen West & Simon Warwick-Smith.

Please do NOT be put off by the title. Trust me, the book itself is very well set-out and not at all sensationalist.

Basically, it is postulated that a number of recent mass-extinction events were caused by a nearby supernova, with ample evidence from diverse scientific fields that seem to bear this out.

Circa 41,000 years ago, there was a blast of radiation that hit SE Asia particilarly hard (the initial flash).
Circa 34,000 years ago, radiation peaks again, and evidence of increased meteoric impacts worldwide (first shock wave).
Circa 16,000 years ago, yet another radiation peak and more impacts (secondary shockwave).
Circa 13,000 years ago, multiple cometary impacts across North America, which kills off most of that region's megafauna and, amongst other things, carve out the "Carolina Bays".

Some Mammoth remains show indications of having been hut with a wave of microscopic particles travelling at extremely high speed immediately prior to the animal's death. Also, indications that this was a Solar System-wide occurrance, with the Moon and Mars subjected to very similar impacts.

Fascinating reading.