This is an artist's rendition of the one-million-year-old star system
called UX Tau A, located approximately 450 light-years away.
Observations from NASA's Spitzer Space Telescope showed a gap
in the dusty planet-forming disk swirling around the system's central
sun-like star.
Spitzer saw a gap in UX Tau A's disk that extends from 0.2 to 56 astronomical
units (an astronomical unit is the distance between the sun and Earth).
The gap extends from the equivalent of Mercury to Pluto in our solar
system, and is sandwiched between thick inner and outer disks on either
side. Astronomers suspect that the gap was carved out by one or more
forming planets.
Such dusty disks are where planets are thought to be born. Dust grains clump
together like snowballs to form larger rocks, and then the bigger rocks collide
to form the cores of planets. When rocks revolve around their central star,
they act like cosmic vacuum cleaners, picking up all the gas and dust in their
path and creating gaps.
Although gaps have been detected in disks swirling around young stars before,
UX Tau A is special because the gap is sandwiched between two thick disks of
dust. An inner thick dusty disk hugs the central star, then, moving outward, there
is a gap, followed by another thick doughnut-shaped disk. Other systems with
gaps contain very little to no dust near the central star. In other words, those gaps
are more like big holes in the centers of disks.
Some scientists suspect that these holes could have been carved out by a
process called photoevaporation. Photoevaporation occurs when radiation from
the central star heats up the gas and dust around it to the point where it
evaporates away. The fact that there is thick disk swirling extremely close to
UX Tau A's central star rules out the photoevaporation scenario. If
photoevaporation from the star played a role, then large amounts of dust would
not be floating so close to the star.
