Supernova in Our Galaxy: Impact on Earth and Frequency of Occurrence

[paulselhi]

I read in various places that a supernova can briefly outshine a galaxy, given the number of stars in our galaxy would it be fair to say that there have been a number of SN in our galaxy since mankind evolved ?

If so what would be the effect on our planet of a SN in the galaxy ? Would the radiation not adversely effect us ?

 

[mgb_phys]

There is a supernova in our galaxy approx every 50years. There is about a 1:10 chance of this being visible to us (most of the other side of the galaxy is hidden by dust) so we observe a supernova about every 3-500 years, this fits in with historical observations.
The crab nebula was around 1000years ago, there was one in 1600 seen by kepler.

If a supernova was close enough the radiation would be a problem but it has to be very close in galactic terms < 100 light years.

 

[paulselhi]

But why do so many sources state that a SN can outshine a galaxy and yet you say that most are hidden by dust and would cause little or no radiation problem

If we can see SN outshining distant galaxies then would not a SN in our galaxy simply swamp it with light ?

 

[mgb_phys]

There is quite a lot of dust - you can't see the 10s of billions of stars in the core because of dust. If a SN went off at the other side of the galaxy any light heading our way would be absorbed by the dust.
Remember that in space there is nothing for the light to bounce off - so we only see the light in a straight line toward us.

Also the light and radiation spread out into a sphere so the intensity decreases by a factor of 4 for each doubling in distance. This is why you have to be so close for the electromagnetic radiation to have any effect.
We did get a large umber of neutrinos passing through Earth following the 1987 supernova but these have very little effect.

A gamma ray burst is much more powerful - I think a GRB going off anywhere in the galaxy would be bad.

 

[marcus]

A gamma ray burst is much more powerful - I think a GRB going off anywhere in the galaxy would be bad.

any opinion as to the mechanism causing GRB?
or some links you would recommend?

interesting topic, maybe should have separate thread: "GRB in our galaxy"

GRB are observed on a daily basis---several per day----but they are so rare that I guess we have no reason to expect a GRB to happen in our own galaxy over human history timespans

they are very brief----at most several minutes duration IIRC---so I suppose in the unlikely event that one occurs in our galaxy the harmful effect would be experienced mainly on one side of the earth, plus I guess major damage to the atmosphere. I haven't thought about this. Would you like to comment on "GRB in our galaxy"?

I think it would be in the spirit (if not the letter) of the original post.

 

[mgb_phys]

I think pairs of neutron stars falling into each other is he current theory of the month.
10 years ago I think I took the first infrared image of a GRB, right instrument on right telescope at the right time - but I don't know anything about them.

I did find this - http://www.pbs.org/wgbh/nova/gamma/milkyway.html

 

[marcus]

can you give me a notion of the effect on Earth (possible damage to atmosphere or biosphere) of a GRB that occurred within say 1000 or 10,000 parsecs?

I never thought about this, but the original poster's question made me wonder.

 

[mgb_phys]

I don't know how correct it is, but the PBS link above suggests that a GRB at 3000 lightyears would appear as bright as the sun and completely destroy the ozone layer - which wouldn't be pleasant.

 

[SpaceTiger]

I'm not a GRB expert, but the last I checked there were two models that were being considered and there was fairly direct evidence for both. One was the hypernova -- basically a supernova from an extremely massive star, and the other was what mgb already mentioned. Evidence for the first was in the form of a supergiant star being observed in the position of a subsequent GRB. I've forgotten the evidence for the second, but they think it explains the shorter GRBs.

Anyway, in both cases, the emission is not thought to be isotropic, so it's not just a question of whether a GRB occurs in our galaxy, but also whether or not it's pointed at us. The results would be pretty devastating if it were.