![Click here for poster version
of PIA12073](https://webarchive.library.unt.edu/eot2008/20090827094308im_/http://photojournal.jpl.nasa.gov/figures/PIA12073_fig1_thumb.jpg)
Poster Version
Here we see two different views of the spiral galaxy, Messier 81. On the
left is an image taken in blue light, while on the right is a
specially-processed version of an image taken with the Spitzer Space
Telescope's infrared array camera (IRAC) at 4.5 microns. The processed
image reveals myriads of tiny arclets, a representative sample of which
are arrowed. Each of these arclets represents a young star stream in the
disk of the galaxy.
Observing the galaxy in the infrared is the only way to directly see the
youngest stars, since the shroud of dust and gas that surrounds them is
opaque to visible light, but transparent in the IR. Even so, the
unprocessed infrared image was still dominated by the light from the
smooth, older disk of the galaxy rather than the faint tracks of young
stars. Further processing using a mathematical technique called Fourier
filtering allowed the team to pick out structures on the physical scale on
which star formation occurs, revealing these streams of young stars
flowing away from their stellar nurseries.
M81 is one of several galaxies that were observed in this way. Taken
together, this sample is the first time that young star streams have been
discovered in the disks of galaxies millions of light years distant,
filling in the "missing link" in the evolution of galaxy disks.