ALMA image of young star HL Tau and its planet-forming disk. Notice the multiple rings and gaps. This means planets are now emerging in the disk, and they are in the process of sweeping their orbits clear of dust and gas. Image via ALMA (NRAO/ESO/NAOJ); C. Brogan, B. Saxton (NRAO/AUI/NSF)
Even for most astronomy enthusiasts, it can be tricky sometimes to distinguish between artist’s illustrations and real images, in part because the artist’s illustrations have gotten so good and so plentiful in recent years. And so one question we’re frequently asked: “Is this a real image?” The image at the top of this post may look at first glance like an artist’s illustration. But it’s not. It’s a real image of a planet-forming disk around the infant star, in this case a sunlike star approximately 450 light-years from Earth, known to astronomers as HL Tau. The Atacama Large Millimeter/submillimeter Array (ALMA) in Chile has recently been upgraded to obtain such sharp images. Its North American managers at the National Radio Astronomy Observatory (NRAO) say this image is:
… the best image ever of planet formation around an infant star…
It is impressive. It reveals in great detail what astronomers just a few decades ago were only theorizing about, and that is that all stars are believed to form within slow-spinning clouds of gas and dust. As the clouds spin, they flatten out into these disks. Over time, the dust particles in the cloud begin to stick together by a process known as acretion, and that process is what ultimately forms the planets like our Earth, and moons like our moon, plus the asteroids, all of which mostly still move (as they did in the original cloud) in this flat space – this disk-like space – encircling the parent star.