Birth of a star- ever captured?

[DJDD]

Hi all,

[qualifying comment- please forgive me if this is a stupid question]


I have been working my way through the Astronomy 162 podcast and reading this forum (lately the discovery of a nova) and was wondering if anyone has captured the "birth" of a star, i.e. when the effects of nuclear fusion are first noticeable at the star's surface?

I imagine that the event would generate an increase in IR, as well as visible light, as compared to the pre-fusion state. Or is the process gradual- that is, it takes time for fusion to really get going?

Although it would be a bit like looking for a needle in a haystack- it seems that needles are found all of the time...

cheers.

[renormalised]

Not that I know of. Actually, the only way you can tell that fusion has begun in the core of a star is to measure the neutrino flux from the core. Normally, it takes light (photons) several million years to reach the surface of a star and any that were produced by nuclear reactions are no exception. For awhile, the light coming from the star would be that generated by it's pre-main sequence state. However, if there was a large and sudden flux of neutrinos from the star, it would indicate that nuclear reactions had begun in the core.

Eventually the light coming from reactions in the core would breach the surface and then it could be said to be shining by the light of nuclear reactions.

[Jazza]

Besides which a star forming is contained within a disk from which the entire solar system forms. This'll obscure the star (protostar) till well after it starts glowin ;)

[Alchemy]

images of the pillars of creation in infrared show newer star forming areas, and i saw one recently in orion of disks forming, .... both hubble shots and would be viewable on the hubble website, but the actual light up?, i havent got to listening to the 162 series yet (have them though) Does professor pogge suggest a light up or a gradual burn so to speak ?

[DJDD]

Thanks for the replies, everyone.



yes, the time delay in getting photos to the surface is there but i imagine it would be quite a sight when a sun begins to really shine.

i imagine that it would be nearly impossible to capture those neutrinos so really it would be limited to the IR/visible mainly.




yes, about this- i wonder how long it takes before the star is less obsucured, liek in other nebulae we observe.

Alchemy, there is not really any mention about how rapidly the fusion reaction proceeds within a star at its birth. It is those details that always leave me wondering.

thanks, again, for the replies.

[renormalised]

Actually, there's not much you can tell from a star about what it's luminosity will be in the time just preceding and proceeding it finally settling down to ZAMS...w.r.t. how it generates it's energy. Actually, the star will most likely be a bit brighter in the pre-main sequence stage as it will be larger than it is when it's core ignites. Both will have some period of variability as the energy generation in the core at either stage is a bit "choppy". The only way you can tell if it's from gravitational collapse or nuclear reactions is if there is a flux of neutrinos, as already mentioned.

The time it would take to drive off it's cocoon of dust and such depends a lot on how big and bright the star is, the density of it's birth cloud etc. Each star is different, but it could take anywhere from a few decades to a few million years.

Nuclear reaction occur at varying rates within the core. Simple (first stage) PP reactions, like the ones occurring in the Sun don't take very long at all, a few milliseconds for some parts of the reaction. However the general conversion of hydrogen into helium can take sometime, several million years. Some parts of the PP reaction are quite slow.

[DJDD]

Thanks for the detailed reply, renormailsed. yet another example of the value of this forum.
Perhaps I was being overly romantic, hoping to see a star "light up"...:)

i always thought the fusion reaction would be very quick but after reading your response I looked up PP reactions on wikipedia for some further light reading...

cheers,
DJDD

[renormalised]

That's good to see you look up the PP reaction on the net. Learn as much as you can :-). The reason why so much hydrogen is converted into helium every second in the Sun's core, is that there are so many reactions going on...when you consider how much hydrogen there is in the core, it's no wonder!!!.

600 million tons of hydrogen are fused into helium every second, with 4 million tons converted into energy every second

[Alchemy]

lecture 14 revealed the details for me ... brief synopsis,

nuclear fusion takes place at 10,000,000 degrees ( in the core) therefore object will glow ( black body radiation) long before the fusion process takes place, depending on size of star the reaction can take a long time to reach the surface ( convection and a couple other processes), 1,000,000 years for our sun. gravity is the driving force till the fusion begins.
Neutrinos give away the process but EXTREMELY hard to capture, for a star way off in a nebula just firing up is outside our technological limit at the moment.

Listen to the supernova lecture ..... fantastic.