When Does a Star Form & What's Best for Life?

[Stephenk53]

I have two questions, firstly, when a star first forms is there a most common type it starts its life as? Such as when it is first big enough to be classified as a star is it usually say a brown dwarf?

Secondly, Is there a type of star that is best for a planet to form life?

 

[newjerseyrunner]

I have two questions, firstly, when a star first forms is there a most common type it starts its life as? Such as when it is first big enough to be classified as a star is it usually say a brown dwarf?

Secondly, Is there a type of star that is best for a planet to form life?

A star is considered a star as soon as it’s large enough to initiate and sustain nuclear fusion in its core. There is a minimum mass for this.

And we only know for sure that yellow, medium sized stars can have life, but theoretically any type could. Ours is nice because it’s fairly stable for long periods of time. Big stars live fast and die young, likely exploding long before any complex life could evolve and small stars last longer but can be turblulent and throw out lots of damaging solar flares.

 

[stefan r]

I have two questions, firstly, when a star first forms is there a most common type it starts its life as? Such as when it is first big enough to be classified as a star is it usually say a brown dwarf?

Secondly, Is there a type of star that is best for a planet to form life?

You might be looking for t-tauri stars. Before that you can have propylids and bok globules,

...Such as when it is first big enough to be classified as a star is it usually say a brown dwarf?..

Once fusion starts the accretion stops. Radiation pushes material away. The collapsing cloud is always much more massive than the star that forms out of it.

Stars can merge. It is not very common.

...

Secondly, Is there a type of star that is best for a planet to form life?

As stated by newjersey runner that is not known for certain. Cannot do statistics with one sample.

"Life forming" is very different question from "advanced life forming". On Earth life appears quickly but Eukaryotes do not show up for over 2 billion years.

Planet systems similar to the Sun are most often found around stars with similar or higher metal content.

Small stars have habitable zones (where surface water is both liquid and ice year round) that are very close to the star. That adds a lot of radiation which will make survival more challenging for life. Large stars tend to blow away the material for planets. The stars also do not live for very long. If a planet did form life would have a very short window to start up before it died.

Advance life probably needs a stable environment. Fewer asteroid impacts after a billion years or so. Few close encounters with other stars that can change the planet's orbit. A moon might be important. Stars that are variable might cause problems too.