New photos of a cosmic cloud rich with young stars offer
tantalizing clues about how those stars came to be.
Scientists recently combined images from the Chandra X-ray
Observatory and the Spitzer Space Telescope to zoom in on the cosmic cloud
Cepheus B, located in our galaxy about 2,400 light years from Earth.
This cloud of mostly hydrogen gas and dust contains a host
of bright young stars whose birth could have been triggered by a nearby massive
star outside the cloud. This star, called HD 217086, is bombarding the region
with strong radiation. While this energetic flow is likely to have evaporated
the cloud's outer layers, it also could have pushed a compression wave into
the cloud that may have driven
star formation by increasing the density of gas in the cloud's interior.
The new observations, which help astronomers estimate the
ages of many of the young stars, support this model of star formation.
In the inner layer of Cepheus B, the scientists found most
of the stars are about 1 million years old, and about 70 or 80 percent of them
have "protoplanetary disks" of matter expected to be on their way to forming
planets - another sign of a young star. In the middle and outer layers of the
cloud, stars are older (between 2 million to 5 million years old) and much less
likely to have protoplanetary disks.
If the massive star outside Cepheus B really did trigger
star formation inside
the cloud, scientists would expect just such an increase in stars' ages
moving farther away from the center of the cloud. The newborn stars resulting
from the hot star's compression wave would be located in the cloud's center,
but only aged stars would be likely near the outskirts, where the compression
wave passed long ago and the big star's strong radiation has squashed more
recent star formation.
This trigger mechanism is just one example of how stars can
come to be. In other situations, stars commonly arise when gas cools and
condenses under its own gravity.
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