Expert: Philip Stahl - 9/2/2008

Question
QUESTION: i swear i read somewhere that for in order a star to be a supernova candidate it has to be over 9 solar masses..is that true, or am i wrong?

but i was browsing some astronomy site and i came across this lifecycle picture that says stars over 1.5 solar masses could supernovae but that doesn't make any sense?

heres the picture----->http://www.enchantedlearning.com/sgifs/Starlifecycle.GIF

ANSWER: Hello,

There is a good deal of confusion mainly because there is a good deal of uncertainty. However, 1.5 M_s (M_s = solar masses) is certainly too low. 1.46 M_s is actually the limit for degenerate matter but that is most likely the Chandrasekhar limit for a white dwarf.

The excellent monograph 'Stellar Structure and Evolution' (a standard text in many astrophysics and stellar evolution courses) quotes a range of possible thresholds for supernova events, from 4M_s up to 10M_s for initiation (Chapter 34, p. 344)

Why so much range of uncertainty? The simple answer is because we have no idea how much mass is lost via strong stellar winds. Obviously if a star starts out at 4M_s but loses 2M_s or more to strong stellar winds it may well fall below the threshold for a supernova.

Alas, the event designated SN1987A has rendered the issues even murkier- since there is no existing developed theory to account for all the mechanisms pertaining to the observed phenomena.

The best approach therefore, is to realize these exotic astrophysical objects are still largely unknown in terms of limits of mass needed to cause a supernova, or even a black hole or neutron star.

Hopefully the insights will improve with further research but right now, all google sites aside, expect more uncertainty than certainty!

---------- FOLLOW-UP ----------

QUESTION: okay i think i confused my self...

for example i thought when they stated a figure such as 1.5 times the mass of the sun meant solar mass in general..but it was times the mass of the sun

how many times of the sun = 9 solar masses?  

Answer
Hello,

Nine solar masses is nine times the mass of the Sun. Again, I think your confusion stems largely from demanding rigid, exact answers from a subject which simply cannot yield them yet. I already explained why one must offer a range of masses (to obtain supernova conditions) and why one cannot have a single explicit and unique answer. The reason has to do with the large question mark of how much initial mass is loss via stellar winds.

Please understand that stellar astrophysics is not like chemistry, where a fixed amount of elements, compounds can always be combined to yield a fixed new compound, e.g.

2H2 + O2 ->  2H2O

Instead there is enormous uncertainty.

For this reason one cannot expect exact answers to many questions!