
Time-resolved 2M-year-old supernova activity found in Earth’s microfossil record - ghosh
http://www.pnas.org/content/113/33/9232.abstract
======
autocorr
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](https://apod.nasa.gov/apod/ap050615.html)
[2]
[https://apod.nasa.gov/apod/ap150816.html](https://apod.nasa.gov/apod/ap150816.html)

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

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

[https://en.wikipedia.org/wiki/Light_echo](https://en.wikipedia.org/wiki/Light_echo)

~~~
jcims
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.

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

~~~
vanderZwan
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?

~~~
iplaw
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).

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

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spectrum1234
What does time resolved mean here?

~~~
cstejerean
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.

~~~
schiffern
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...](http://physicsworld.com/cws/article/news/2002/feb/13/supernova-
link-to-ancient-extinction)

------
wiz21c
Could someone describe what it's like to live on earth during a (close)
supernova ? Why can this event trigger an extinction ?

~~~
pxndx
Related what-if: [https://what-if.xkcd.com/73/](https://what-if.xkcd.com/73/)

~~~
acqq
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](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."

~~~
acqq
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](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."

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

~~~
acqq
[http://heasarc.gsfc.nasa.gov/W3Browse/star-
catalog/cns3.html](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).

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

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spectrum1234
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.

~~~
tdy721
The signal is about 800 Million Years Long, it shows a slow seeding of Earth
with Fe60. It has nothing to do with dinosaurs.

