Supernova 7000 ly Away: Impact on Earth and Light Visibility

[Ronhrin]

I've read in several news and science sites that a star roughly 7000 ly away from the sun is going to become a supernova in a very short time.

Most science websites say that due to the distance of the star and Earth's protective atmosphere this supernova will not pose any risk to life on earth.

but now comes my question that I can't find no answer for, even though life on Earth is perfectly safe when the radiation of this supernova arrives here, what will happen to the light. I mean everyone knows that when a supernova goes off, it shines more than it's entire host galaxy for a period between 30 to 80 days, if in a faraway galaxy the light of a supernova becomes more bright than an entire galaxy, what will we see when this nova goes off, I mean, 7000 ly is damn close from the sun, if this supernova is visible during the night time will it's light shine stronger than our sun and during those 30 to 80 days of supernova will the night become day?

 

[chroot]

I suspect you're talking about Eta Carinae.

Consider for a moment that the entirety of our Milky Way Galaxy, when both the Sun and Moon are below the horizon, doesn't even produce enough light to read a newspaper headline by.

If Eta Carinae goes supernova, it will likely be one of the brightest objects in the night sky for years, and perhaps even brighter than the moon, but it will be no contest at all for the Sun.

Personally, I hope it happens in my lifetime!

- Warren

 

[Ronhrin]

I suspect you're talking about Eta Carinae.

Consider for a moment that the entirety of our Milky Way Galaxy, when both the Sun and Moon are below the horizon, doesn't even produce enough light to read a newspaper headline by.

If Eta Carinae goes supernova, it will likely be one of the brightest objects in the night sky for years, and perhaps even brighter than the moon, but it will be no contest at all for the Sun.

Personally, I hope it happens in my lifetime!

- Warren

Yes, I'm referring to Eta Carinae, I have seen many pictures about supernovas in several galaxys, and in each one of them the light of the supernova almost offuscate the entire host galaxy.

our milky way has 100.000 ly of size from one side to the other, 7000 ly is almost "around the corner", after all the pictures I've seen of supernovas it's very difficult to imagine the brightness that this particular nova will have to a Earth observer.

I also hope this one will happen during my lifetime, I think supernovas are one of the most beaiutiful events in the universe.

 

[chroot]

You can look up at Sagittarius at night and see our Galaxy's core. It's about 25,000 light years away. Now consider an object (Eta Carinae, gone supernova) with the same luminosity as the entire core, but at only 7,000 light-years distance. That's roughly one-quarter the distance, so it would impart sixteen times the energy on the Earth as the Galactic core.

Now, vision is complex and its sensitivity is logarithmic. Also, the Galactic core is rather spread out, while the Eta Carinae would be essentially a point source. If you factor in these facts, it seems reasonable that Eta Carinae would be somewhere between 1 and probably 1,000 times as bright (subjectively) as the Galactic core.

Since the Galactic core is so dim you need a decently dark sky to see it at all (something that's becoming rare these days...) it's not terribly likely that Eta Carinae's supernova will be much brighter than some nearby stars. It would be utterly spectacular if it were competition for the Moon, but there's just no way at all it could possibly compete with good ol' Sol.

- Warren

 

[Chronos]

A useful comparion would be supernova 1006, which had an estimated apparent magnitude of -7.5. The star believed to be its remnant is virtually at the same distance from Earth as eta carinae - 7000 light years. This translates into an absolute magnitude of -19.2. The brightest observed supernova to date is SN2006gy with an absolute magnitude of -22. At a distance of 7000 light years this star would have had an apparent magnitude of about -10.4. The full moon has an apparent magnitude of -12.6. SN2006gy is also thought to be a freakishly bright and unusua beast called a pair instability supernova, so it was probably brighter than eta carinae would be were it to core collapse for our viewing pleasure. Typical supernovas do not maintain their peak brightness very long and generally fade back into obscurity within a few months. There is nothing to suggest eta c would behave any differently.

 

[Brad_Ad23]

You can look up at Sagittarius at night and see our Galaxy's core. It's about 25,000 light years away. Now consider an object (Eta Carinae, gone supernova) with the same luminosity as the entire core, but at only 7,000 light-years distance. That's roughly one-quarter the distance, so it would impart sixteen times the energy on the Earth as the Galactic core.

Now, vision is complex and its sensitivity is logarithmic. Also, the Galactic core is rather spread out, while the Eta Carinae would be essentially a point source. If you factor in these facts, it seems reasonable that Eta Carinae would be somewhere between 1 and probably 1,000 times as bright (subjectively) as the Galactic core.

Since the Galactic core is so dim you need a decently dark sky to see it at all (something that's becoming rare these days...) it's not terribly likely that Eta Carinae's supernova will be much brighter than some nearby stars. It would be utterly spectacular if it were competition for the Moon, but there's just no way at all it could possibly compete with good ol' Sol.

- Warren

Yes, but are you not forgetting to take into account several aspects when you say this:
a)Extinction effects that block out a lot of light from the galactic core
b)Even though we can see towards the core, that still isn't the full galaxy.


At any rate, Chronos is pretty much right. At 7500 light years away, good ol' Eta would have a bright apparent magnitude of -10.2.

This is bright enough probably to be seen in the day time (assuming the sun is not nearby), but is still 1000 times dimmer than a full moon.

 

[Chronos]

One magnitude equals the 5th root of 100 [~2.5119], so the relative luminosity formula is:
M/m = 2.5119^(M - m), where M is the magnitude of the brighter object and m the dimmer, making the full moon about 9x brighter than a magnitude -10.2 object.

 

[Brad_Ad23]

One magnitude equals the 5th root of 100 [~2.5119], so the relative luminosity formula is:
M/m = 2.5119^(M - m), where M is the magnitude of the brighter object and m the dimmer, making the full moon about 9x brighter than a magnitude -10.2 object.

Yes, I stand corrected on that error (two too many zeros )

 

[OSalcido]

-10.4? :
That's amazing!

I suspect that Eta Carinae being a binary could possibly alter those numbers a bit, though. Maybe as bright as a full moon?

 

[Chronos]

Possibly, but, not enough to rival the full moon IMO. Brad's oversight was nothing more than that, and irrelevant to the issue. Take out the numbers and you get the same substance.

 

[cepheid]

I just heard an astronomer on CBC radio's Quirks and Quarks corroborate what some of you have been saying...Eta Carinae wouldn't appear as bright as the full moon if it went supernova, but it would be brighter than Venus and easily visible in the daytime. He didn't quote an apparent visual magnitude, since few people know what that means.

 

[Brad_Ad23]

I just heard an astronomer on CBC radio's Quirks and Quarks corroborate what some of you have been saying...Eta Carinae wouldn't appear as bright as the full moon if it went supernova, but it would be brighter than Venus and easily visible in the daytime. He didn't quote an apparent visual magnitude, since few people know what that means.

I should hope it corroborates.

As an issue, if Eta were a binary system, then when one of the partners went supernova it would be a lot less bright than what it would be in the above examples.

 

[dimensionless]

Does anyone know what the odds are that this will occur in our life times?

 

[Chronos]

Not good, but perhaps within 100,000 years.

 

[magnetar]

Eta Carinae is about 100 times bigger than our sun!

So I wonder if it will collapse into a black hole directly? instead of going
supernova??

Thank you !

 

[George Jones]

Eta Carinae is about 100 times bigger than our sun!

So I wonder if it will collapse into a black hole directly? instead of going
supernova??

Thank you !

When Eta Carinae goes supernova, it might be big enough to blow itself to smithereens, with no neutron star or black hole left behind.

Recently, there has a been a lot of stuff in the media about http://www.berkeley.edu/news/media/releases/2007/05/07_supernova.shtml" , the brightest (in absolute terms) supernova ever seen. SN 2006gy may be the first observed occurence of a pair-instability supernova, and Eta Carinae may go supernova in the same way.

Massive stars produce high energy radiation, and this radiation supplies part of the pressure necessary to keep the star from collapsing. If the radiation has high enough energy, collisions of photons can produce electron-antielectron pairs. After such collisions, the photons no longer exist, so this process reduces the radiation pressure. If the pressure is reduced enough, the star collapses, producing a very violent explostion that leaves little behind, i.e., no black hole.

Nathan Smith http://www.cbc.ca/quirks/media/2006-2007/mp3/qq-2007-05-12a.mp3" on the Quirks and Quarks programme mentioned by cepheid.