ALMA telescope spies a planetary system in process of being born


With amazing clarity, astronomers have spied a solar system in the act of being born.

At the center is HL Tau, an infant star that is believed to be no more than 1 million years old. It is surrounded by hazy, concentric rings of material that scientists say will coalesce into planets.

The remarkable image was captured by ALMA, the Atacama Large Millimeter/submillimeter Array. ALMA is a network of 66 radio telescopes in Chile’s Atacama desert that is a joint project of the U.S. National Science Foundation’s National Radio Astronomy Observatory (NRAO) and partners in Canada, Europe, Asia and Chile.


“The fact that we can see planets being born will help us understand not only how planets form around other stars but also the origin of our own solar system,” Crystal Brogan, an associate astronomer at NRAO’s headquarters in Charlottesville, Va., said in a statement.

Sitting more than 3 miles above sea level, the massive ALMA antennas don’t see visible light like we do. Instead, they capture longer wavelengths in the radio portion of the light spectrum.

That’s lucky for astronomers. In the visible light spectrum, HL Tau is blocked by a massive cloud of gas and dust.

The sun-like star lies in the constellation Taurus and is about 450 light years away. NRAO astronomers were pointing their antennas toward it as they were testing a new configuration designed to improve the observatory’s capabilities. (With the antennas spaced about 15 kilometers apart, they are able to see well enough to spot a penny that’s more than 110 kilometers away.)

With the array trained on HL Tau, the telescopes got a clear shot of a protoplanetary disk. Such disks are made of dust and ice particles that over tens of millions of years combine into planets and other solar system denizens such as asteroids and comets.

In the new image, the clear gaps between the concentric rings of dust are a sign that the planet-forming process has begun, astronomers said. Until now, only computer models could produce images with this level of precision.

“The first time I saw this image I thought it was actually probably a simulation. It was just way too good,” NRAO Director Tony Beasley said in a video.

The scientists expressed surprise that the planet-forming process around HL Tau could be so far along since the star is so young. Nevertheless, the dark lanes between the concentric circles of bright orange matter are a sign that the proto-planets around the young star are already big enough to assemble dust and larger objects with the force of their own gravity.

“We see gaps in the radio emission in this disk that’s orbiting the star,” Beasley said. “Quite likely those gaps are being caused by planetesimals – young planets which are forming around the star.”

Someday, astronomers might be see these nascent proto-planets directly by observing the system at higher frequencies, he said.

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