Question

When do we say that a star is born?

when the interstellar cloud collapses
when the interstellar matter achieves the Jeans instability
when fusion of hydrogen atoms into helium atoms starts
when the star leaves the main sequence

Answer 1

A star is born when the interstellar cloud collapses and fusion of hydrogen atoms into helium atoms begins, which occurs when the core temperature exceeds 10 to 12 million K.

Step-by-step explanation:

A star is considered to be born when the interstellar cloud collapses and reaches a point of high enough density to initiate the fusion of hydrogen atoms into helium atoms. This process occurs when the core temperature of the star exceeds 10 to 12 million K. At this point, the star is in equilibrium and is considered to have reached the main sequence.