Definition: Given a passage and a query based on the passage, generate an unambiguous, concise and simple answer to the query from information in the passage. Note that the answer may not be present in exact form.
Input: Eventually, radiation pressure from the star blows away the envelope and the new star begins its evolution. The properties and lifetime of the new star depend on the amount of gas that remains trapped. A star like our sun has a lifetime of about 10 billion years and is just middle-aged, with another five billion years or so left. And once the fusion reactions begin, they exert an outward pressure. As long as the inward force of gravity and the outward force generated by the fusion reactions are equal, the star remains stable. Clouds of gas are common in our galaxy and in other galaxies like ours. These clouds are called nebulae. A typical nebula is many light-years across and contains enough mass to make several thousand stars the size of our sun. The majority of the gas in nebulae consists of molecules of hydrogen and helium--but most nebulae also contain atoms of other elements, as well as some surprisingly complex organic molecules. STAR BIRTHS are started when the interstellar matter in gas clouds, such as the Eagle Nebula shown here, compresses and fuses. Irregularities in the density of the gas causes a net gravitational force that pulls the gas molecules closer together. NGC 6326, a planetary nebula with glowing wisps of outpouring gas that are lit up by a binary central star. A planetary nebula, often abbreviated as PN or plural PNe, is a kind of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from old red giant stars late in their lives. A star is born when atoms of light elements are squeezed under enough pressure for their nuclei to undergo fusion. All stars are the result of a balance of forces: the force of gravity compresses atoms in interstellar gas until the fusion reactions begin. Most planetary nebulae form at the end of the star's life, during the red giant phase, when the outer layers of the star are expelled by strong stellar winds. After most of the red giant's atmosphere is dissipated, the ultraviolet radiation of the hot luminous core, called a planetary nebula nucleus (PNN), ionizes the ejected material. A planetary nebula, abbreviated as PN or plural PNe, is a kind of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The word nebula is Latin for mist or cloud, and the term planetary nebula is a misnomer that originated in the 1780s with astronomer William Herschel because, when viewed through his telescope, these objects resemble the rounded shapes of planets. Herschel's name for these objects was popularly adopted and A planetary nebula, often abbreviated as PN or plural PNe, is a kind of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from old red giant stars late in their lives.[2] The word nebula is Latin for mist or cloud, and the term planetary nebula is a misnomer that originated in the 1780s with astronomer William ... Theoretical models predict that planetary nebulae can form from main-sequence stars of between one and eight solar masses, which puts the progenitor star's age at greater than 40 million years. Although there are a few hundred known open clusters within that age range, a variety of reasons limit the chances of finding a planetary nebula within. Planetary nebula - Membership in clusters. 1  Planetary nebulae have been detected as members in four Galactic globular clusters: Messier 15, Messier 22, NGC 6441 and Palomar 6. Query: at what point does a star form from a nebula
Output:
A star is born when atoms of light elements are squeezed under enough pressure for their nuclei to undergo fusion.