8 highlights of radio astronomy in 2021

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8 highlights of radio astronomy in 2021

From the Moon to the farthest quasar, the big radio astronomy stories of 2021.

Artwork depicting the accretion disk around a supermassive black hole in a quasar, creating a jet of matter blowing outwards. Credit: NOIRLab/NSF/AURA/J. da Silva

The human eye is an amazing piece of equipment. It's so useful it likely evolved dozens of time independently — as my friend Julia Sweeney says (paraphrased), "What good is half an eye? Probably about half as good as an eye." — and allows us a way to sense the world and Universe around us with decent precision.

But... it's only sensitive to a very narrow range of light. It took a long time for humans to figure this out, but what we call visible light is only thin slice of the kind of light that's out there. Gamma rays, X-rays, ultraviolet, infrared, microwaves... these are all forms of light with wavelengths too short or too long for the human eye to register.

If we only look to the heavens so see the visible light it sends us, we're missing out on well over 99.9% of what's out there.

Radio and millimeter waves are profoundly important things to be able to detect. So many objects emit them, from the Sun and planets to dust clouds forming stars and electrons whizzing around magnetic field lines around black holes and supernovae. By studying this form of light we get much more information about the Universe, and keen insight into the engines that drive it.

Every year there are incredible new discoveries made because astronomers and engineers built the Atacama Large Millimeter/submillimeter Array, the immense Greenbank Radio Telescope, the Very Large Array, and more; huge dishes or multiple combined dishes to scan the sky and, well, see what we can see, even if we can't see them per se.

So it was my pleasure to work with my friends at the National Radio Astronomy Observatory (NRAO) to present some amazing long-wavelength astronomical highlights from 2021. We combed through the year's research, found eight wonderful stories, and I wrote and did the voice-over for beautiful animations that NRAO created to explain these phenomena. Fasten your seatbelts! We're going to travel from the nearest astronomical object in the Universe out to its most distant reaches.

The Moon gets some radar love

Radio telescopes don't just receive long-wavelength light from objects; some can transmit it to bounce off nearby solar system bodies like the Moon. This technique, called synthetic aperture radar, can be used to map the Moon to an incredible resolution of just 5 meters. The initial tests have been so successful that NRAO received a multi-million dollar NSF grant to expand its efforts.

Galaxies running out of gas

Our Milky Way galaxy is actively making stars, and many galaxies we see are fecund indeed. But others appear to have their star formation being quenched, where star birth is suppressed or even stagnant. To learn why, astronomers turned to ALMA to find out.

The DNA of a galactic jet

The nearby galaxy M87 has an enormous central supermassive black hole, famous for posing for the first ever high-resolution image of such a beast, which is blasting out a powerful beam of matter and energy that stretches for thousands of light years. Detailed observations using the Very Large Array show that along some its length the jet is actually a pair of entwined corkscrew spirals, a double helix much like DNA.

Massive star birth

We see stars in the process of formation in nearby gas clouds with quite a bit of detail, but finding massive stars — ones with many times the mass of the Sun — in the throes of formation is more difficult. However, looking at the nebula W51, astronomers found three such monsters being created, helping them understand what's different for them than for more modest stars.

Massive planet formation

One of the more amazing recent advances in astronomy is being able to see planets forming around other stars in huge swirling disks of gas and dust. Elias-2-27 is nearby still-forming star where a massive planet is also collecting itself. ALMA observations show the chaos that such an event sows.

Black hole chews up a star and detonates it

This is one of my favorites stories from 2021: A star went supernova in a galaxy 500 million light years from Earth. Routine, right? Yeah, well, they also found evidence that the reason this supernova occurred is because a black hole collided with the star, fell to the center, and made such a mess in the star's core that it exploded. Holy wow!

Star formation in the Milky Way

How do stars in our galaxy form? In a huge survey of the sky, astronomers used the Very Large Array to map hydrogen gas, as well as complex molecules like methanol and formaldehyde, and saw star factories churning them out, as well as the expanding debris from stars that exploded long ago.

Quasar distance record

In 2021, a type of active galaxy called a quasar was found so far away its light took over 13 billion years to reach us — a distance record. At its heart is a huge black hole powering its energetic emission... which is actually a problem, since we're not sure how it could've grown to such a large size so quickly after the formation of the Universe itself.


Pretty cool, the things we can do when we open our eyes past what our eyes alone can see! And if you think these are nifty, then check out the lists we did for 2020 and for 2019.

When I was in graduate school at the University of Virginia working toward my degree, we would often walk up the street to the NRAO HQ to attend talks by local and visiting radio astronomers (and also to play volleyball, since they had a great court there). It was a lot of fun to listen to people talk about their observations using instruments totally different than what I used, and to hear about new discoveries as they happened. It is a huge honor and pleasure to be able to work with NRAO now to create these annual highlights. I hope you like them too.

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