Spiral Galaxy NGC 2403 in Subaru (APOD 5 Jul 2006)

orin stepanek · Post by **orin stepanek** » Wed Jul 05, 2006 2:35 pm

http://antwrp.gsfc.nasa.gov/apod/ap060705.html

This galaxy; home of one of the largest supernova; appears to be rather small as far as galaxies go. I couldn't find any references as to it's size that I could understand. Is it small as galaxies go or is it an optical illusion? How many light years from a supernova would a planet have to be to be safe from ill effects from such a happening? That may really be a tough

to answer. Just a curiosity thing.
Orin

Galactic Groove · Post by **Galactic Groove** » Wed Jul 05, 2006 3:21 pm

Hi Orin,
I don't know, I think it looks pretty big and rather spectacular as well! It looks to be a rather..... (I'm not sure of the word so I'll use) "diverse" galaxy in respect to what you can see in it.

As for being safe from a supernova.....
Throughout Earth's history there have been many mass extinctions, somewhere between 7 and 11 I believe. Each one of these mass extinctions can be traced back to radiation released from individual stars that went supernova long long long ago. As our solar system rotated around the galaxy, we passed through these radiation zones, ultimately ending life during that time period (but luckily for us, life managed to hold on by a thread). I know this doesn't exactly answer your question about how far away you'd have to be to be safe but it is rather interesting

BMAONE23 · Post by **BMAONE23** » Wed Jul 05, 2006 4:44 pm

Looking at the image at the numerous red emission nebula, it appears that some of them stretch for thousands of light years. maybe tens of thousands (depending on the actual size of the galaxy.).

Qev · Post by **Qev** » Thu Jul 06, 2006 6:21 am

Actually, I believe the reference on that page was to it being one of the brightest supernovae of recent times, not the biggest. Meaning it had one of the highest apparent magnitudes (ie. brightness against the sky) of modern supernova.

NGC 2403, at roughly 10 million light years, spans less than half a degree on the sky, approximately 23.4 arc minutes. A bit of math and this comes out to 70000 light years in diameter, more or less. So it's smaller than spirals like the Milky Way or Andromeda, but those two are big spirals.

As for supernova danger to Earth, a 'normal' supernova would have to be very close for it to have any deleterious effects on the planet. The most recent estimation that I've seen gives a distance of 25-30 light years as the minimum safe distance. Mathematically, we could expect to see a supernova within that distance of Earth every billion years or so. Hypernovae / gamma ray bursts are a different story, and could probably be dangerous out to a couple thousand light years.

harry · Post by **harry** » Thu Jul 06, 2006 7:56 am

Hello all

Qev you may be right.
But!

I read this last week,,,,,,,,,,,,,there is a link indicating 150 light years for a safe distance.

But! this is not the problem.

Our solar system, and I have read it somewhere had gone through a nebula a few hundred million years ago.

Its not just the supernova coming to us, its us heading towards the unknown.

I will go and look for the link.

harry · Post by **harry** » Thu Jul 06, 2006 9:57 am

Hello All

Supernova poised to go off near Earth

http://www.newscientist.com/article.ns?id=dn2311

Too close for comfort
But do not panic yet. "Very soon" could mean hundreds of millions of years in the future. And that is just as well, because we are only 150 light years away from HR 8210 at present - well short of the 160 to 200 light years thought to be the minimum safe distance from a supernova. If it did let fly, the high-energy electromagnetic radiation and cosmic rays it released would destroy Earth's ozone layer within minutes, giving life little chance of survival.

This would not be the first time a supernova has changed the course of life on Earth. In 2001, Jesus Maiz-Apellaniz and colleagues from the Space Telescope Science Institute in Baltimore, Maryland, found a "smoking gun" supernova remnant, in the group of stars known as the Scorpius- Centaurus association.

The timing of the supernova corresponds to an otherwise mysterious deposit of heavy isotopes in deep Earth cores and to a mass marine extinction two million years ago. At the time, Scorpius-Centaurus was around twice as far away from Earth as HR 8210 is now.

Fortunately, it will take time for HR 8210 to accumulate the mass it needs. Preliminary calculations by Rosanne di Stefano at the Harvard-Smithsonian Center suggest this may take hundreds of millions of years. By that time it will be much further away, she says, though she still needs to confirm exactly how far. "I want to be sure I'm right."

But will similar stars threaten us before then? "The fact that there's such a system so close to us suggests maybe these objects are not so rare," says Latham

Massive star may explode any day

http://www.abc.net.au/science/news/stories/s775452.htm

Smile and live another day

Qev · Post by **Qev** » Fri Jul 07, 2006 9:29 pm

harry wrote:Hello all

Qev you may be right.
But!

I read this last week,,,,,,,,,,,,,there is a link indicating 150 light years for a safe distance.

I believe the 25-30 lightyear estimates are somewhat more recent than the 150 lightyear distance you've quoted, judging by the article dates and the content of the articles themselves. But hey, this is science, and things are changing all the time, so I could be wrong.

harry · Post by **harry** » Sat Jul 08, 2006 3:14 am

Hello Qev

25 light years you would think it would be a safe distance.

Time will come that the solar system will be placed in chaos way before our sun gives up.