Shredding and Stitching Stars with u/Andromeda321 (Yvette Cendes)

If a black hole shreds a star and nobody is around to hear it, does it make a sound? To find out, Dr. Charles Liu and co-host Allen Liu welcome Professor Yvette Cendes, (aka u/Andromeda321 on Reddit), a Radio Astronomer studying transient radio signals from space.

As always, though, we start off with the day’s joyfully cool cosmic thing, a report by the Dark Energy Survey that seems to show that the amount of dark energy originally described as the cosmological constant by Albert Einstein might in fact be variable. As Prof. Cendes explains, the data indicates that universal expansion is still accelerating but the rate might be changing.

After Yvette explains what she does, and how radio astronomy works in concert with optical astronomy to deliver a more complete understanding, Chuck asks her to explain Tidal Disruption Events, or TDEs, about which she’s a world expert. A TDE is when a star wanders too close to a supermassive black hole and ends up getting shredded. Yvette prefers to call them “Shredders.”

Our first audience question comes from Nachama, who asks, “When will the black hole in the Milky Way eat the Sun?” The good news, according to Yvette, is that will never happen. As she explains, black holes actually don’t suck any more than anything that massive would, and we’re 25-30,000 light years away from Sagittarius A* – too far away to worry about.

Next, Chuck asks Yvette about one of the most famous transient signals we’ve ever found, the so called “Wow!” signal detected in 1977 by Jerry Ehman at the now-defunct Xavier Observatory in Ohio. Because the signal looked exactly like what might be expected if it were of extraterrestrial origin, Ehman circled it on the printout and wrote, “Wow!” Unfortunately, it never repeated. The most likely explanation, according to Dr. Cendes, is that it was some sort of manmade interference, although the signal is currently being reinvestigated.

Yvette recounts how she ended up ended up as a first-term professor at the University of Oregon after studying in the Netherlands and Toronto and working at Harvard. Then she answers an audience question from Yan Min, who asks, “Where is the best place in the world to study astronomy? I live in New York – Is it New York?” Unfortunately for Yankees fans, Yvette says it would most likely be Cambridge, Massachusetts thanks to Harvard, which has the biggest number of astronomers under one roof and operates the Chandra X-Ray Observatory, and M.I.T. on the other side of town if you get bored.

Chuck asks Yvette what happens after a black hole shreds a star. Shredders, she explains, are rare. In our own Milky Way, they probably happen once every million years. Once a TDE is classified by optical astronomers, Yvette and her team point their radio telescopes at the tidal radius outside of the event horizon to discern the outflows weeks, months and even years after the initial event.

He also asks Yvette if she has any hobbies to help her decompress from thinking about violent events in the universe. She likes to cross stitch, the “original pixel art.” Yvette shows us a cross stitch she made of the James Webb Space Telescope complex mirror, another featuring an 8-bit Mario screen with the words “What doesn’t kill me makes me smaller,” and a third with objects in the Solar System. She also embroiders and shows us a hoop featuring the constellations visible in the northern hemisphere night sky.

We end with Yvette and Allen schooling Chuck about Reddit’s immense reach and value in scientific discourse. One subreddit, called r/Space, has “27 million intelligent lifeforms” subscribed to it. On Reddit, Yvette’s username is u/Andromeda321, and she’s one of the top users on the platform over 1 million karma points. She’s known for starting her posts that explain or comment on recent discoveries with the phrase, “Astronomer here!”

If you’d like to follow Dr. Yvette Cendes, you can find her on Reddit,