What Would a Supernova Look like from Earth?

[starshelle]

If a supernova happened to one of our closer red giants like Antares and Betelgeuse, I'm very curious how that would appear to us on earth. <br /><br />Would the night sky be serene and normal, only to suddenly have the star grow larger before our eyes? Or would the star gradually grow brighter and brighter until it was so bright it would be available for days at a time before gradually fading?<br /><br />I know the Chinese recorded at least one "guest star" that became four times brigher than Venus and could be seen in daylight for 23 days, but I can't help but wonder if the star just SUDDENLY became brighter, or if it would become brighter over a period of time. I'm unclear how quickly this event would occur before our eyes. Thanks for indulging my curousity. <img src="/images/icons/smile.gif" />

 

[Maddad]

http://www-supernova.lbl.gov/public/figures/snvideo.html<br />I'm not sure what you mean by suddenly. They reach full brightness in several days. The light curve at the page above is probably a couple of months long from beginning to end, with full brightness showing up pretty near the beginning.<br /><br />Supernova 1987A was 160,000 light-years away from us. Had it been as close as Sirius, a very close star, at maximum it would have been 100 times brighter than our full moon.

 

[thalion]

Unfortunately, we've never observed the *exact* beginning of a supernova, so that question has no precise answer. In all likelihood, the rise would be rapid, but by no means instantaneous.

 

[thalion]

The situation isn't quite that pessimistic. If I remember correctly, the neutrino burst immediately precedes the increase in brightness; theoretically, if we could pinpoint the origin of the neutrino burst, we could find the culprit and observe the SN from the very beginning.

 

[nexium]

My guess is the nuetrinos would arrive about a millisecond ahead of the visablle light. If I recall correctly it was estimated 4 seconds before the light for the 1987 super nova which was 10,000? times farther than Sirus. Neil

 

[Maddad]

Yup, pretty close. Sirius is 8.6 light-years away, and SN1987A was about 170,000, or 20,000 times as far.<br /><br />It's something I still don't understand about supernova neutrinos. Why do we see them first, and then the light? Is the light held up at the source, giving the neutrinos time to get out first?

 

[Maddad]

Do you have a figure for the mass of the neutrino relative to the electron? Something like 1 part in 10,000?

 

[starshelle]

I want to apologize for my delay in getting back to this. I wrote this shortly before my Christmas vacation and the holidays turned out to be much more hectic than I had anticipated. I wanted to thank those who responded. I found some of the information to be very useful. I wish I hadn't used the word "suddenly" though. I should have tried to have been more specific. <br /><br />The scenario I've always been very curious about is how a supernova would appear to the naked eye. Could someone be looking out of his bedroom window at night and within minutes a star that was shining normally become noticeably brighter right before his eyes? I always wondered if a supernova appeared in a nearby star, if the star would become brighter before the naked eye within minutes, or if the process of a star growing brighter would take hours, or maybe it wouldn't be even noticeable for days? <br /><br />Thanks to the responses I understand now that it does indeed appear that the supernova would take several days to reach the full brightness. So most likely if a supernova did take place nearby the results wouldn't be instantaneous, but it does sound as though it would still be visibly noticeable to the naked eye fairly soon. I just want to make sure I understand the information correctly, so I’m going to attempt to summarize the information that was presented.<br /><br />If a nearby star went supernova it would take several days for it to reach full brightness. So someone looking at the stars from their bedroom window might notice a particular star seems much brighter than it had been the previous night. The person wouldn’t be able to see the star grow instantaneously brighter though but it would look noticeably brighter. Then over the next few days the star would become increasingly brighter, until the supernova reached its zenith and be could even be seen in the daylight. Then over the next couple of months the supernova would gradually fade. Does that this sound correct?<br />

 

[Maddad]

http://www.supernovae.net/light98s.jpg<br />Well, you got me curious enough to go look up some more light curves like the one above. This one appears to have taken ten days to reach maximum brightness.<br /><br />http://www.npl.washington.edu/AV/altvw23.html<br />Interesting. The energy of a supernova is mostly escaping neutrinos. What we see when we look at it has only one part in 10,000 of the total energy.<br /><br />http://www.astro.uu.nl/~strous/AA/en/antwoorden/sterren.html<br />Finally! The magnitude increase for a supernova is 15. I seem to remember 17 from somewhere, but am unable to confirm it.<br /><br />http://www.badastronomy.com/phpBB/viewtopic.php?t=11101&start=50<br />Jerry Jensen on the Bad Astronomy forum pegs supernovae brightness at neg 14 to neg 21 with an average of neg 19.5. I was ballpark correct. Trouble is that we don't know the brightness of the progenitor, so we don't know the absolute change in brightness.