Stars form out of the gravitational collapse of large clouds of
interstellar gas and dust. Originally very tenuous, the density of
these clouds increases as they contract and a central star
builds-up. As a consequence, the temperature at the center also
increases as pressure goes up. After a while, many thousands of years
actually, the temperature in the central protostar gets high enough
that the "baby star" starts shining by itself. This is pretty much like
a metal rod that "glows" red after being heated enough. At that stage,
the original cloud of material as also dissipated, it becomes
transparent. Most of it has been accreted by the star itself and the
central object finally becomes visible to our telescopes. A
star is born.
The first young stars were identified by Alfred Joy in 1945. He
classified 11 objects into a new class he called the "T-Tauri Stars",
after the brightest of the 11 peculiar stars he had just found, T
Tauri. Since then, the name T Tauri stars has always been associated
with newborn stars. We now know that these objects are very similar to
what our own sun must have looked like when it was a few million years
old only. By comparison our sun, in its midlife today, is about 5
billion years old, a thousand times older. A few thousands of T Tauri
stars have been discovered to date.
This week's image provides a close view of T Tauri itself. As can be
seen, T Tauri and its close environment are much more
complicated than what is expected from the simplified scenario
described above. First of all T Tauri is not single, it is a binary
system. Two stars can be seen on the image, they are indicated more
clearly here. The companion, T
Tauri South, was detected in the near infrared J-band for the first
time by the authors. It is the discovery image we present this week.
Circumstellar material, dust particles close to the stars that
scatter light, is also visible as the extended Halo. It is a mixture
of material leftover from the original cloud that gave birth to T
Tauri (at large scale) and from material ejected by the stars as they
formed (at small scales). The latter process is known as mass-loss, or
"stellar winds". Our Sun looses material too, but at a much lower rate than
the T Tauri stars do. It is this "wind" from the Sun that is responsible
for the Northern light for example.
This week's images show us that T Tauri, and by analogy the whole
star formation process, is very complicated. There is still a number of
issues we just don't understand yet. Because our Sun and planetary system
are most likely the outcome of the same process, it is mandatory that
studies like the one presented this week be carried out if we hope to
understand our origins one day.
This week's image is part of a series of images obtained at the
Canada-France-Hawaii Telescope with adaptive optics since 1993 to
monitor the evolution of the complicated T Tauri system. Different AO
systems developed by the University of Hawaii adaptive optics
group were used. Images were obtained mostly in the near-infrared,
at 1.25, 1.65 and 2.2 microns, the so-called J-, H- and K-bands
respectively. On all the images, North is up and East to the left, as
we see in the sky.
Technical description: