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dtilque
2010-May-19, 08:04 AM
Besides SN1987A and the various historical supernovae seen in our galaxy, how many have been observed in the Local Group of galaxies?

Nereid
2010-May-19, 08:29 AM
Besides SN1987A and the various historical supernovae seen in our galaxy, how many have been observed in the Local Group of galaxies?
The first non-MW supernova observed was SN1885, or S Andromedae (http://seds.org/messier/more/m031_sAnd.html), the one and only SN observed in M31 (the Andromeda galaxy), to date.

According to this 1980 Sidney van den Bergh paper (http://adsabs.harvard.edu/abs/1983PASP...95..388V), it was the only Local Group SN observed in the previous 100 years (the next nearest SN I could find, doing a quick search, is SN1993J, in M81).

Now the Local Group of 1980 certainly had fewer galaxies than the Local Group of today! But, AFAIK, none of the new additions have been graced by a SN in the last 100 years.

If you expand your definition of "observed" somewhat, to include light echoes, then several have been observed in the LMC (http://www.nature.com/nature/journal/v438/n7071/full/nature04365.html) (and maybe other Local Group galaxies too).

dtilque
2010-May-20, 05:17 AM
Just one? Supposedly there are an average of two per century for large spirals such as Andromeda. I'd have expected about 3 or 4 in that period in M31 and M33. Combined with the dearth of them in our own galaxy, this is looking suspicious...

M31 is tilted in our view. Could some be hiding in the dust/gas clouds? M33 is nearly face on, so we should see any sn there. I sense a conspiracy...

Hornblower
2010-May-20, 08:23 AM
Just one? Supposedly there are an average of two per century for large spirals such as Andromeda. I'd have expected about 3 or 4 in that period in M31 and M33. Combined with the dearth of them in our own galaxy, this is looking suspicious...

M31 is tilted in our view. Could some be hiding in the dust/gas clouds? M33 is nearly face on, so we should see any sn there. I sense a conspiracy...

I sense only an artifact of the irregular nature of a series of random events. Dry spells lasting two or three times the long-term average interval, along with bursts of above-average frequency, are not uncommon. For all we know, prior centuries could have had several supernovae in M31 that went undetected, but could have been detected if today's observing capability and practices been in place.

Based on published total magnitudes, I estimate that M33 has about 1/6 as many stars as M31. I would expect a correspondingly lower incidence of supernovae.

Romanus
2010-May-21, 12:49 AM
Yes, there is no real pattern to SN occurrence--that said, I sincerely hope we're overdue for a good SN in either M33 or M31. It wouldn't be SN 1987A--a little back-of-the-envelope math suggests a likely peak magnitude of about 7 mag for a Type II--but with a suite of new tools to investigate one from surface and orbit the windfall could be proportionately greater.

That said, I'm optimistic enough to think that the odds of seeing one in my lifetime are better than even. :)

dtilque
2010-May-21, 06:52 AM
I sense only an artifact of the irregular nature of a series of random events. Dry spells lasting two or three times the long-term average interval, along with bursts of above-average frequency, are not uncommon.
Yeah, I knew that. I was just joking. The Illuminati ain't that powerful yet (I hope).



Based on published total magnitudes, I estimate that M33 has about 1/6 as many stars as M31. I would expect a correspondingly lower incidence of supernovae.
I hadn't realized M33 was that small.

Messier Tidy Upper
2010-May-21, 11:57 AM
Some galaxies in the local group are well hidden behind our own Milky Way (eg. Maffei I & II - http://en.wikipedia.org/wiki/Maffei_1 , Saggittarius dwarf ; http://en.wikipedia.org/wiki/Sagittarius_Dwarf_Irregular_Galaxy) and others such as M82 (the cigar galaxy : http://en.wikipedia.org/wiki/Messier_82 ) are very dusty with lots of material that may potentially obscure and redden any supernovae that take place in them - now or in the past. So it seems to me we could be missing a few that have occurred sadly.

ngc3314
2010-May-21, 12:50 PM
... others such as M82 (the cigar galaxy : http://en.wikipedia.org/wiki/Messier_82 ) are very dusty with lots of material that may potentially obscure and redden any supernovae that take place in them - now or in the past. So it seems to me we could be missing a few that have occurred sadly.

Like this one (http://berkeley.edu/news/media/releases/2009/05/27_radioSN.shtml) in M82.

Looking at the past record, I don't think we have any reliable information on possible Local Group SN outside our own galaxy before SN1885 in Andromeda, and things could be pretty spotty up to the start of the Harvard sky patrol photography (around 1920). M31 and the Milky Way have between them by far the lion's share of potential progenitors for either kind of supernova; the faint dwarfs don't add significantly to the pool. (This means that a whole generation of astronomers, and neutrino folks who were astrophysicists even if they had trouble admitting it, were pretty lucky seeing SN1987A in the LMC).

chornedsnorkack
2010-May-21, 03:19 PM
Based on published total magnitudes, I estimate that M33 has about 1/6 as many stars as M31. I would expect a correspondingly lower incidence of supernovae.

I would not. M33 has relatively active star formation, and contains NGC604, slightly bigger though slightly dimmer than Tarantula. By contrast, while Andromeda Nebula does have young stars and supernovae, it is much quieter relative to the mass of old stars, resembling more a lenticular galaxy than Milky Way.

In terms of star formation rate, how would you compare the size of young populations of Milky Way, Andromeda, Triangulum and Large Magellanic Cloud?