Feast your eyes, my friends, on this — by far the most detailed image ever of a young star and its protoplanetary disk. Here you can see the young star HL Tau, which is only about one million years old, as dust and gas swirl around it, gradually forming into planets and asteroids. Believe it or not, a few billion years ago, this is what our very own Solar System would’ve looked like.
This photo was captured by ALMA, the Atacama Large Millimeter/submillimeter Array — a giant telescope consisting of 66 individual antennas, located high up in the Atacama desert in northern Chile. According to the European Southern Observatory (ESO) which operates ALMA, this image comes from some of the telescopes first observations in its “new and most powerful mode” (ALMA has been under construction for years, but only recently have they installed enough antennas and moved them into the right position for high-res deep-space imaging).
In the middle of the image is HL Tau, a young star about 450 light years distant in the constellation Taurus. Previous observations had told us that there was a dust cloud around HL Tau, but it wasn’t until ALMA gazed upon the star that the nature of the dust cloud became apparent. Seeing a protoplanetary disk in such detail is groundbreaking — and seeing such a disk around a star that’s just one million years old is astounding. We had previously thought that it took a lot longer for a star’s cloud of dust and gas to accrete, through gravity, into planets and asteroids.
Hubble image of the region around HL Tau
This image compares the size of the Solar System with HL Tauri and its surrounding protoplanetary disc. Although the star is much smaller than the Sun, the disc around HL Tauri stretches out to almost three times as far from the star as Neptune is from the Sun.
ALMA, high up in the Atacama desert in Chile, is a rather large telescope
The gaps between the rings of the disk, incidentally, are the telltale sign that planets and asteroids are currently being assembled. As gravity causes larger and larger accretions of rock and gas, they sweep up more dust and gas — effectively snowballing and carving out gaps in the disk as they continue to orbit the star. This is the same process by which the rings of Saturn were formed.
Back here on Earth, this high-resolution observation of HL Tau’s protoplanetary disk will hopefully tell us a lot about how our own Solar System formed, some four billion years ago. Previously, we could only make educated guess and simulate the formation of planets and stars — but now, thanks to ALMA, we can actually watch it happen in the real world, in almost real time. Science is pretty awesome.
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