Craig, many thanks for going to all that trouble for me, I'm very grateful. I see now why I was having so much trouble finding this answer - I didn't know what T-Tauri stars were about.
I have the Cambridge Encyclopedia of Stars which is a very comprehensive book, but as educational as it is, right now at this stage, it is far too advanced for me in many areas. But I will slowly come to understand the info in it in time to come no doubt. Thanks to your help, the last couple of days I have been reading up on Protostars and T-Tauri stars. I'm glad you added that clarification at the end of your post, as the biggest part of my question was after how long do they "turn on their light". So, another thank you.
What I'm understanding so far is this (say, a star the same size as ours):
- A prostar spends 10-15 million years at this stage.
Quote:
from Wikki:
When the protostellar cloud has approximately reached the stable condition of hydrostatic equilibrium, a protostar forms at the core.[56] These pre-main sequence stars are often surrounded by a protoplanetary disk. The period of gravitational contraction lasts for about 10–15 million years.
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Then, the star goes on to be a T Tauri star, which spends around 100 million years in this stage before it goes on to be a main sequence star.
Quote:
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from Wikki: T Tauri stars are pre-main sequence stars – the youngest visible F, G, K, M spectral type stars (<2 Solar mass). Their surface temperatures are similar to those of main sequence stars of the same mass, but they are significantly more luminous because their radii are larger. Their central temperatures are too low for hydrogen fusion. Instead, they are powered by gravitational energy released as the stars contract towards the main sequence, which they reach after about 100 million years.
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Then, once on the main sequence, they stay there for around 10 billion years.
Quote:
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from Wikki: Stars spend about 90% of their lifetime fusing hydrogen to produce helium in high-temperature and high-pressure reactions near the core. Such stars are said to be on the main sequence and are called dwarf stars
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Like you, I had to source the information on these different stages from different sources
(with thanks to you giving me what to search for).
So, am I on the right track?
