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# G1.9+03 Supernova question?

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### #1 Gvs

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Posted 30 September 2019 - 03:38 PM

G1.9+03 is regarded as the youngest supernova in the Milky Way Galaxy.

Located at 25000ly away,  the event reached Earth 110-140 years ago.

If the second statement is true, than the Crab would nebula, located 6500ly away, actually would be a younger event, as it was recorded in 1054.

Cassiopeia A is still the youngest Nova is 11K ly away.

Can someone please corroborate these assumptions?

The Crab Nebula is currently:

420″ × 290" or 7 arcmin across (11ly moving at 0.5c in 900 years!)

Now G1.9+03 is 2.5 arcmin across, at 25K light years, that's a huge size!  In 140 years!!!!

Can someone please explain this, as it doesn't seem to make physical sense.

If a Galaxy like the Milky Way has an Supernova once every 100 years.  We are due for a fair amount of events during the past 1000 years.

Does anyone know of more events in the past 1000 years?

They will be interesting to watch, if they occur in our lifetime!

Will Eta Carinae be one of them?

Edited by Gvs, 30 September 2019 - 03:41 PM.

### #2 JamesMStephens

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Posted 30 September 2019 - 04:40 PM

Youngest in earth's time frame, so not corrected for light travel time.  I think.

### #3 robin_astro

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Posted 01 October 2019 - 08:50 AM

Re your 2nd question the approximate mean expansion rates for the two supernova remnants are

crab  radius =  6500*sin(3.5 arcmin) ~6.5lyr  in~900 years = ~0.007c or 2100km/s

(The current expansion rate is ~1500km/s)

G1.9+03 radius = 25000*sin(1.25 arcmin) = 9.1lyr in 140 years =~0.065c or 20000km/s

The crab expansion rate is reasonable given that the initial velocity of the material thrown out in a supernova explosion is typically 10-20000km/s.  The mean expansion rate for G1.9+03 is unusually high though as the article explains

"In the case of G1.9+0.3 the material is expanding outwards at almost 35 million miles per hour, or about 5% the speed of light, an unprecedented expansion speed for a supernova remnant."

Re your third question, yes there may be supernova in our galaxy that have "already exploded" but the first we can know about any event in the universe  is when the light (or other signals such as gravitational waves which also travel at light speed) reach us

Cheers

Robin

Edited by robin_astro, 01 October 2019 - 08:52 AM.

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