Planets stake their claim around infant star

HL Tau dust disk

FINDING THEIR SPOT  A dense disk of gas and dust surrounds, HL Tau, a star located about 450 light-years away in the constellation Taurus. Grooves in the gas and dust hint at the growth of young planets.


As a baby, our solar system probably looked something like this.

At the center of this newly released telescope image is HL Tau, a star located about 450 light-years away in the constellation Taurus. A dense disk of gas and dust surrounds the star, which is a youthful million years old.

But the most striking features are the dark gaps, which astronomers suspect are carved out by developing planets that sweep up material as they loop around their sun. In only a million years or so, planetary embryos that began as pebbles have apparently grown massive enough to clear out their own orbital paths.

This unprecedented image of a nascent planetary system comes from the Atacama Large Millimeter/submillimeter Array, or ALMA, a network of several dozen radio dishes located in the high-elevation desert of northern Chile. The dishes detect wavelengths of light that are sensitive to cosmic dust grains; the spacing between dishes — as much as 16 kilometers — allows astronomers to capture incredibly fine detail such as the thin grooves. (For scale, the innermost ring is about 10 times as far from the star as Earth is from the sun.)

Hints of gaps around young stars have been seen before, but this is the sharpest image of them to date. Seeing rings around such a juvenile star probably means that planets can grow faster than theorists have predicted. Scientists hope to combine the observations of HL Tau with those of other nurseries to figure out how planetary systems like our own form.

Focus on a planetary baby picture




Estimated distance to HL Tau (over 4 quadrillion kilometers)



Distance from ALMA at which the array can detect a penny-sized object, providing the resolution needed to see gaps in the disk



The age of HL Tau compared with that of the sun

Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

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