T Tauri Stars (taken from CSIRO: Australia Telescope National facility)
T Tauri stars are young, irregular, variable stars. They are protostars of 3 solar masses or less, still collapsing and
undergoing mass-loss. This material is ejected into space at speeds up to 500,000 km h -1 at a rate of 10-7 to 10-8 solar
masses per year. The T Tauri phase may last 10 million years during which a mass equal to the Sun is ejected. Spectral
analysis shows that these stars rotate rapidly and have high abundances of lithium, an element that is consumed early in
a star's life. They are located just to the right of the main sequence on an HR diagram.
Credit: NASA, John Krist (Space Telescope Science Institute), Karl Stapelfeldt (Jet
Propulsion Laboratory), Jeff Hester (Arizona State University), Chris Burrows
(European Space Agency/Space Telescope Science Institute)
HST images of hot gas being ejected from XZ Tauri, a T Tauri-type star. The
gas bubble is channeled by the strong magnetic field of the binary system and
ejected at speeds up to 540,000 km h-1. The bubble extends almost 100 billion
km into space.
The early phases of a star's formation end when the temperature within
its core is high enough for hydrogen nuclei (protons) to fuse together. This initiation of so-called hydrogen-burning marks
the star's transition onto the main sequence, the next stage of its existence.
from http://www.kcvs.ca/martin/astro/au/unit4/92/chp9_2.htm
When does a protostar cease being a protostar and become a "real" star? To answer this question
recall a number of ideas developed earlier:
1. As a protostar collapses its core temperature and density increase. This is a critical step
because it tells you that the frequency of collisions between the atoms in the star (primarily
hydrogen) goes up rapidly. As well, the increasing temperature means that the collisions are
becoming increasingly violent.
2. There is a direct link between the temperature of a gas and velocity with which the particles in
the gas move. The hotter the gas, the faster the particles move.
3. Because the atoms in the interior of a star are ionized and positively charged - they repel each
other. Another name for this is Coulomb repulsion. Normally Coulomb repulsion pushes
protons away from each other. However, if two protons are brought to within about 10 -15 m of
each other a new force - The Strong Nuclear Force takes over. This force only operates at very
close range but when it does it is about one thousand times stronger than the Coulomb force
and is attractive. The protons fuse together.
4. When light elements such as Hydrogen and Helium fuse they release energy
Nuclear Fusion: Average stars like our sun produce energy through nuclear fusion by the proton
proton chain reaction. In the core of the sun, temperatures are so high that the positive hydrogen
nuclei are moving fast enough that they can overcome their positive charges and combine
together. In Hydrogen fusion, four hydrogen nuclei join to produce one helium nucleus. One
Helium nucleus has a mass that is 0.7 percent less than the four hydrogen nuclei so it appears that
there is some missing mass. It turns out that the missing mass is converted into energy by the
equation e=mc squared. In this equation, e represents energy, m represents the missing mass,
and c squared is the speed of light squared.