Abstract
A newly born star can be thought of as having been born when the core temperature of the protostar reaches about 10 million K. At this temperature, hydrogen fusion can occur efficiently by the so-called proton-proton chain. This moment, when ignition of the fusion process occurs, will halt any further gravitational collapse of the protostar. The star’s interior structure stabilizes, with the thermal energy created by nuclear fusion maintaining a balance between gravity and pressure. This important balancing act is called gravitational equilibrium. It is also sometimes referred to as hydrostatic equilibrium. The star is now a hydrogen-burning main sequence star.
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Notes
- 1.
We will discuss the proton-proton chain in much greater detail in the following sections on the Sun and the main sequence.
- 2.
See the section on the Sun for a full discussion on gravitational equilibrium.
- 3.
When astronomers refer to a star’s following a specific evolutionary track, or moving on an H-R diagram, what they really mean is the star’s luminosity and/or temperature changes. Thus, the position of the star on the H-R diagram will change.
- 4.
The theoretical calculations were developed by the Japanese astrophysicist C. Hayashi, and the phase a protostar undergoes before it reaches the main sequence is called the Hayashi phase.
- 5.
There are a few examples of nebulae in which protostars are currently forming and which are observable in the section on emission nebulae. You will not, however, see protostars, just the region within which they reside.
- 6.
We shall see in a later section why the Sun is opaque.
- 7.
Recall from an earlier section that the luminosity is proportional to the square of the radius and to the fourth power of the surface temperature.
- 8.
There is no mass-luminosity relationship for white dwarfs, giant stars and supergiant stars.
- 9.
Not surprisingly, there are been recent reports of stars with masses in excess of 200 M☉
, as large as 250 M☉
. How these stars can exist is a matter of much research and fierce debate. - 10.
This figure of 0.08
M☉ is about 80 times the mass of Jupiter. - 11.
By “ordinary” we mean matter composed of atoms, to distinguish it from “dark matter,” whatever that may be!
- 12.
Yes, we have seen this before, but it is such a magnificent, and important, object that it warrants a second look.
- 13.
Stars named after the FU Orionis prototype are also worth observing. It is now believed that the activity of FU Orionis (and similar stars) is related to the T Tauri variables. T Tauri variations may result from instabilities within and interactions with the surrounding accretion disk. FU Orionis activity is caused by a dramatic increase in instability due to the dumping of large amounts of material onto an accompanying star. Many astronomers believe that all T Tauri stars probably go through FU Orionis-type behavior at least once in their development.
- 14.
Eventually an amateur astronomer will image a protostar. It’s only a matter of time and money.
- 15.
We are talking about spiral galaxies here, not elliptical. Elliptical galaxies are believed to be the result of mergers between spiral galaxies where the rate of star formation is very high initially—a starburst galaxy—and then falls. We shall cover this topic in a later chapter.
- 16.
Pronounced “aitch 2.”
- 17.
It isn’t a cloud at all; this is just the name ancient astronomers gave the galaxy before they knew what it really was!
, as large as 250 M☉
. How these stars can exist is a matter of much research and fierce debate.
M☉ is about 80 times the mass of Jupiter.Author information
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Inglis, M. (2015). Star Birth. In: Astrophysics Is Easy!. The Patrick Moore Practical Astronomy Series. Springer, Cham. https://doi.org/10.1007/978-3-319-11644-0_6
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DOI: https://doi.org/10.1007/978-3-319-11644-0_6
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