Time-resolved 2M-year-old supernova activity found in Earth’s microfossil record | Hacker News Reader

Time-resolved 2M-year-old supernova activity found in Earth’s microfossil record

pnas.org

103 pointsghosh27 comments

For those curious, this supernova is unfortunately too old to find the supernova remnant that was left behind. The most famous SNRs are Cas A [1] and M1/the Crab Nebula [2].

When the core of a massive star collapses, the resulting explosion launches the rest of the star surrounding the core outwards. Near to the star, this explosion proceeds as an unimpeded free expansion for a few hundred years, but the ejecta eventually impacts the gas between the stars, the interstellar medium. The ejecta then goes through two phases, an adiabatic phase (ie can't efficiently radiate away the heat) and radiative phase (ie can efficiently radiate away the heat). The adiabatic phase ends after around a couple ten thousand years, and the radiative phase ends after a few hundred thousand. As the remnant evolves, the gas becomes cooler and less dense, until eventually it's indistinguishable from the rest of the interstellar medium. So, if this supernova occurred around 2 million years ago, we shouldn't be able to observe the remnant. A shame!

[1] https://apod.nasa.gov/apod/ap050615.html [2] https://apod.nasa.gov/apod/ap150816.html

I understand it is possible to observe reflections of large supernova level events. A possibility?

Our Galaxy is 100K light years across, the light would already have dissipated.

I didn't know about this. Googled and found the Wikipedia about light echoes. Very neat.

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

Seems like black holes could have this same effect on light from supernovas due to gravitational lensing. In fact, there should be some part of the area around a black hole in which the lensing effect bends light 180 degrees. With a big enough telescope we could observe our own solar system as it was thousands of years ago.

Just to add one thing because it's neato: the core collapses the moment when the star begins doing fusion on iron, which is the first fusion in the chain of successive fusions to absorb energy instead of produce it.

This process is weaponized in the novel Iron Sunrise by Charlie Stross.

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

FYI: Supernova link to ancient extinction [2002] http://physicsworld.com/cws/article/news/2002/feb/13/superno...

So that article also mentions this Fe60, and the same time window. What did the recent article add? Is it "just" a confirmation of the hypothesis?

> What did the recent article add?

Yes. This is my question as well.

The 2002 article mentions that the radioisotope was found in the crust. The new article mentions that the radioisotope was found in a biologically-produced magnetite crystal. I think that the general thesis is that -- yes, we are made of star stuff (that the supernova material deposited on Earth has seen verified biological uptake).

Here is a link to the full html article [1] and the pdf [2] The links are a bit hard to find from the abstract page. The html version has some messed up formatting but the pdf is fine. The DOI is: 10.1073/pnas.1601040113

[1] http://www.pnas.org/content/113/33/9232.full [2] http://www.pnas.org/content/113/33/9232.full.pdf

What does time resolved mean here?

I believe it means dated, meaning they were able to determine roughly how old those atoms are, presumably based on the age of the sediment in which it was found.

Here time resolved means not just dated, but having a definitive "shape" through time (the temporal analog to "resolving" an astronomical object to more than just a single pixel). As others have pointed out, supernova derived Fe-60 merely 'dating' to 2 million years ago was already known.[1]

Supporting quote from the abstract:

>Our results show that the (60)Fe signal onset occurs around 2.6 Ma to 2.8 Ma, near the lower Pleistocene boundary, terminates around 1.7 Ma, and peaks at about 2.2 Ma.

[1] http://physicsworld.com/cws/article/news/2002/feb/13/superno...

Could someone describe what it's like to live on earth during a (close) supernova ? Why can this event trigger an extinction ?

Related what-if: https://what-if.xkcd.com/73/

But it wouldn't help answering the question, because a supernova doesn't just eject the neutrinos, it's the intentionally "illogical" question for what-if that is answered there.

For the answer to the question "what it's like to live on earth during a (close) supernova" the starting point is here:

https://en.wikipedia.org/wiki/Near-Earth_supernova

If it's "roughly less than 10 to 300 parsecs (30 to 1000 light-years) away" it will "have noticeable effects on its biosphere."

"It is estimated that a Type II supernova closer than eight parsecs (26 light-years) would destroy more than half of the Earth's ozone layer."

"Type Ia supernovae are thought to be potentially the most dangerous if they occur close enough to the Earth. Because Type Ia supernovae arise from dim, common white dwarf stars, it is likely that a supernova that could affect the Earth will occur unpredictably and take place in a star system that is not well studied."

And, for an idea of how many such stars we see, the list of visible stars not farther than 50 light years:

http://www.atlasoftheuniverse.com/50lys.html

"This is a map of every star within 50 light years visible with the naked eye from Earth. There are 133 stars marked on this map." "There are roughly 1400 star systems within this volume of space containing 2000 stars, so this map only shows the brightest 10% of all the star systems, but most of the fainter stars are red dwarfs."

Is there a comprehensive list of ALL stars within 50/100/200/etc light years?

http://heasarc.gsfc.nasa.gov/W3Browse/star-catalog/cns3.html

"Gliese Catalog of Nearby Stars, 3rd Edition, contains all known stars as of 1991 that are within 25 parsecs of the Sun."

(25 pc == 81 ly) Only 213 KB gzipped, I count less than 4000 lines total.

Since then there were new satellites which collected much more total stars, and the coming will collect even more, but I don't know how the near stars are affected (probably less).

Just like in classic sci-fi Dragon's Egg. Supernova happens at the same time hominims begin to become human.

If this is what killed the dinosaurs this seems like really bad news. Being on Mars won't really be putting our eggs in multiple baskets then.

Wasn't that much earlier?

Dinosaurs died out 65-ish million years ago

The signal is about 800 Million Years Long, it shows a slow seeding of Earth with Fe60. It has nothing to do with dinosaurs.

It's too soon to worry about natural events with a timescale of millions of years.

A single million years from now, we'll be either extinct or unimaginably different from today.

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