How close does a supernova has to be to be lethal?

  • Context: Graduate 
  • Thread starter Thread starter SubTachyon
  • Start date Start date
  • Tags Tags
    Supernova
Click For Summary

Discussion Overview

The discussion revolves around the potential lethal effects of supernovae on Earth, specifically examining how close a supernova would need to be to pose a threat to life. Participants explore various factors such as the type of supernova, the energy emitted, and the implications of radiation exposure, with a focus on theoretical calculations and assumptions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant argues that a supernova 50 light years away could be dangerous, citing a need for calculations to assess radiation exposure, but notes several unknowns such as the duration of energy expulsion and the type of radiation emitted.
  • Another participant suggests that the distance at which a supernova poses a threat depends on its energy and type, referencing a specific supernova (2006gy) to illustrate the flux calculations.
  • A claim is made that a typical type Ia or II supernova would need to be less than 30 light years away to be lethal, while gamma-ray bursts (GRBs) could pose a threat from a distance of a couple thousand light years.
  • It is noted that interstellar matter, such as hydrogen, could attenuate harmful radiation through Compton scattering, affecting the potential threat level.
  • One participant introduces the concept of starquakes as another potential threat to life, suggesting that supernovae are not the only cosmic events to consider.
  • A later reply mentions a consensus from a lunch conversation that the lethal distance is in the tens of light years, emphasizing that gamma rays would primarily destroy the ozone layer rather than direct radiation being the main threat.
  • Participants discuss rough calculations regarding energy absorption and the impact on ozone, suggesting a range of 10% to 50% of high UV radiation could be significant.

Areas of Agreement / Disagreement

Participants express differing views on the lethal distance of supernovae, with some suggesting it could be as close as 30 light years, while others propose varying distances based on different factors. There is no clear consensus on the exact distance or the mechanisms involved.

Contextual Notes

Participants acknowledge several uncertainties, including the duration of radiation exposure, the specific types of radiation emitted, and the effects of interstellar matter on radiation attenuation. The calculations and assumptions presented are not universally agreed upon.

SubTachyon
Messages
19
Reaction score
0
So one guy comes to me and says that he doesn't believe that a supernova 50ly away would be dangerous enough to pose a lethal threat to us. I contradicted him because based on my general reading supernovas (depending on their magnitude) between at least a 100 to 3000 light years away would expose us and our atmosphere to overwhelming levels of radiation. However then I thought of going further and actually doing some calculations myself to prove my point but I soon discovered the task is much more difficult than I would like it to be:

I start with the assumption that the supernova is 50ly away and radiates the energy worth of 1 Foe (10^44j). This gives me the value of 36Mj per metre squared at our distance. However here come the unknowns:
- Over what duration is this energy expelled? Are we looking at most of it shining through in 100 seconds or a month or the whole year?
- What % of that is short-wavelength radiation? Because unless we get kilowats worth of infrared radiation we are really mainly concerned with the harmful stuff right?
- How much can our atmosphere take? How many wats worth of gamma and x-rays do we have to be exposed to in order to deplete our ozone layer and kill us?

I am assuming there will be people here who dealt with a similar issue at some point and can perhaps at least talk from experience if not maths?
 
Astronomy news on Phys.org
A typical [type Ia or II] supernova would need to be less than 30 light years distant to pose any threat to life on earth. GRB's, on the other hand, could be a threat over a couple thousand light years. Another factor is what lies between Earth and a supernova. A significant quantity of interstellar hydrogen would cause compton scattering, further attenuating the deadlier wavelengths. For some recreational math, see here:
http://www.tass-survey.org/richmond/answers/snrisks.txt
 
Last edited by a moderator:
Astronuc said:
Distance would obviously depend on the energy/type of SN.

And in case of an anisotropic supernova (e.g. due to bipolar jets) it will depend on its orientation.
 
This was a topic of a lunch conversation and the consensus was that the lethal distance was in the tens of light years. It wouldn't be the direct radiation that would kill us but the gamma rays would destroy the ozone layer.

To do a rough calculations

1) it really doesn't matter since you are looking at total energy absorbed
2) you can put in order 10% to 50% in high UV
3) for this you calculate the number of ozone atoms and compare to the number of photons that get generated

If you are impatient, here is someone that has already worked it out... :-) :-) :-)

http://iopscience.iop.org/0004-637X/585/2/1169/56170.text.html
 

Similar threads

Undergrad Abundant water from primordial supernovae at cosmic dawn
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Supernova 7000 ly Away: Impact on Earth and Light Visibility
  • · Replies 15 ·
Replies
15
Views
5K
Undergrad How Can We Measure Properties of Distant Planets and Stars?
  • · Replies 12 ·
Replies
12
Views
3K
Graduate NASA's DART spaceship has hit the Dimorphos asteroid: what now?
  • · Replies 4 ·
Replies
4
Views
3K
Writing: Input Wanted How Close Can Spaceships Safely Approach Black Holes?
  • · Replies 10 ·
Replies
10
Views
4K
Undergrad How does the solar wind affect Earth's atmosphere?
  • · Replies 3 ·
Replies
3
Views
2K
How Does Relativity Affect the Perception of Time Between Supernovae?
  • · Replies 1 ·
Replies
1
Views
2K
Stargazing How do space telescopes detect non-visible light?
  • · Replies 4 ·
Replies
4
Views
6K
High School Clarification on how old the Universe is
  • · Replies 11 ·
Replies
11
Views
3K
Undergrad How Does Quantum Measurement Influence Reality Splitting in Many Worlds Theory?
  • · Replies 30 ·
2
Replies
30
Views
4K