archive: RE: SETI Why would anyone look forward to sharing this galaxy?

RE: SETI Why would anyone look forward to sharing this galaxy?

jerry and judy ( )
Fri, 9 Oct 1998 11:20:26 -0600

>Precedence: bulk
>I have wondered if one reason we are not being inundated with
>ETI signals, radio or optical, is that our area of space has suffered
>natural cosmic catastrophes in the relatively recent past, such as
>a supernova, which we on Earth managed to avoid, which other
>planets may not have been so lucky about?

According to THE GUIDE TO THE GALAXY by Nigel Henbest & Heather Couper
(Cambridge University Press 1994, ISBN 0-521-45882-X) which I highly
recommend for its estimated depictions of this side of the Galaxy, there
are 5 loops in our stellar neighborhood that are discernible from the earth
that might be the remnants of ancient supernovas. We find ourselves in the
center of a small one called the Local Bubble. For reference, Antares and
Hadar are located in Loop I, Polaris and the Owl Nebula in Loop II,
Rastaban (Draco) and Enif (Pegasus) in Loop III. Rigel and Arneb (Alpha
Leporis) are in a much larger, older, less prominent loop, centered 300 LYs
past Rigel, encircling the famous, smaller but brighter Barnard's Loop.
Loops within loops! a complicated history of nearby and ancient supernovas.
Since our star is very old compared to these massive stars that come and go
(supernova) within a 100 million years or less, AND because our system is
moving a little faster (12 Kps) than the local standard of rest, it's
difficult to guess whether any of these violent expansions had any effect
on Earth's history. We're pretty well 'insulated'.

See the list below for some very recent supernovas, which thankfully, were
very much farther away.

>I know I always wonder whenever I see an image of a supernova in
>some distant galaxy who might have been in that neighborhood and
>if they could have escaped in time?
>Here is one such article on the subject:
>And related ones:

Eta Carinae (9000 LYs away) has been found to be spewing nitrogen from its
core, a sign of instability? The Hubble has shown us that the star is
cocooned in dust ejected from the 1843 outburst, when it flared up to
become the second
brightest star in the sky! If the dust wasn't there it would probably be
confirmed to be 5 million times brighter than the sun. And because the
dust cocoon is trapping its heat, Eta Carina is the brightest infrared
source in the heavens! 'Looks like it will be a humdinger!, we're lucky
that it's not as close to us as some recent supernovas.

Not to worry though, supernovas in 1006 AD and December of 185 AD (now
called RCW 86) have recently been found to have exploded only 3500 and
4500 LYs away!, respectively. And more comfort, the one in Scorpio,
SN1006, is considered to be the brightest SN in the last 2000 years, as
seen from earth (based on records of its duration and estimated light curve
etc.), and we're still here! (grin).

Tycho's (11 November 1572), Cass A (probably 16 August 1680) and 3c58
(1181 AD) were all (coincidentally?) 8000 to 9000 LYs away behind the
stars of Cassiopeia.

Kepler's SN went off in 1604 AD (13000 LYs away, just this side of the
galaxy's nucleus and except for a huge shock to the Church, 'fixed stars'
and all that rot, no lasting effects have resulted. (grinning) Two
supernovas within a working lifetime!, as if to mock those who still clung
to the old ideas!

In another part of the Perseus Arm, 7000 LYs away, the supernova that became
the Crab Nebula (pulsar) blew in 1054, but only 2000 years earlier, about
1000 BC, IC 443 popped in the same neighborhood, and it was 1000 LYs
closer to Earth.

Not to end this listing on a scary note but, there is some agreement that
NGC 6164-65, right next door to the whopper of 1006 AD, will probably go
supernova shortly (and it's just in front and to the side of the Lagoon
Nebula - so it's less than 5200 LYs away!). If it's as big as its
neighbor was, it will probably be quite impressive for us! (hopefully no
more than that).