Astronomers have used the recently-upgraded ALMA (Atacama Large Millimeter/submillimeter Array) telescope to capture an astoundingly-detailed image of planets forming around a young star - an image that is being dubbed ALMA’s “Best Image Ever”.
Asteroids, comets and planets are thought to be formed in protoplanetary disks: large, rotating disks surrounding new stars, made up of leftover materials from the formation of the stars themselves. ALMA's revolutionary image reveals a protoplanetary disk around HL Tau, a sun-like star about 450 light years from Earth. Not only that, but the image reveals multiple concentric rings, separated by clearly defined gaps; these structures indicate the presence of multiple young, planet-like bodies ‘sweeping’ their orbits clear of debris in the disk.
Images with this level of detail were previously only seen in computer models and artists’ concept sketches of planet formation - this image provides reassuring proof that nature and theory are very much in agreement! What was surprising to astronomers, however, is that planet formation appears to be underway around such a very young star; this was not previously expected, and means planet formation theories may need a bit of a rethink.
It is worth noting that HL Tau is hidden in visible light, since it is obscured by a massive envelope of dust and gas. But ALMA observes at longer wavelengths than the human eye can see, and it is able to peer right through the dust to study what’s going on at the core of the dust cloud. And ALMA’s resolution is impressive: 35 milliarcseconds, which is ten times better than the Hubble Space Telescope’s resolution, and equivalent to being able to see a penny seen from more than a hundred kilometres away!
I think it’s really amazing that barely 20 years ago, we didn’t really know whether there were any planets in the universe other than those in our own Solar System. Now we have reason to believe there are hundreds of billions of planets in our own galaxy alone - many of them similar to the Earth - and we’re learning more and more about them every day. What an exciting time to be an astronomer!
This new image from the Atacama Large Millimeter/submillimeter Array (ALMA) reveals extraordinarily fine detail that has never been seen before in the planet-forming disk around a young star. These are the first observations that have used ALMA in its near-final configuration and the sharpest pictures ever made at submillimeter wavelengths. The new results are an enormous step forward in the observation of how protoplanetary disks develop and how planets form.