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Review: AAS Hangout — The Black Hole in the Center of our Galaxy

Jessica Lu (from the Institute for Astronomy, University of Hawaii) talks about the black hole at the center of our galaxy in a Hangout from the American Astronomical Society with Alberto Conti, Jason Kalirai, & Tony Darnell. Woot :) Earth is in the suburbs of the galaxy and the center is very different. It has a supermassive black hole, massive clusters of stars that are being born in great, great quantities, far more than stars out here close to the earth. So it is the place to look to understand star formation, black hole formation, and how supermassive black holes affect their environment. JWST will give us a very sharp view. Most black holes are a few times the mass of the sun and born from a big star, but the black hole in the center is a supermassive black hole, 4 million times the mass of our sun and unlike anything else in our galaxy. We don’t know how such big black holes form, but we think they’re at the center of every galaxy. It’s the only supermassive black hole where we can see stars whizzing around it. No theory said that every galaxy would have a supermassive black hole in the center, but that’s what the data from Hubble says. Only after we found very active supermassive black holes in other galaxies did we look for one in our own quiet galaxy. The center of the galaxy is hard to see unless you can see through dust — which you can in infrared. The future of astronomy is in the infrared! And stars in the center of the galaxy are mostly older, redder stars, and accreting material on the supermassive black hole emits more brightly at infrared wavelengths. Stars are so densely packed you could put a million stars in a sphere with the radius of the distance between us and Alpha Centauri. The night sky would be bright as day, filled with stars. Very young and very old stars — almost 10 billion years old. Why the gap? We don’t know. Jets are not always perpendicular to accretion discs or the galaxy — those are just the ones we can see. Their orientation is determined by magnetic fields. Our black hole isn’t launching a jet. Ground-based telescopes with adaptive optics are NOT better than space-based telescopes. How do we know if black holes are spinning? It takes a very long experiment. Orbits of nearby stars will change very slightly if the black hole is spinning. The spin of the galaxy isn’t caused by the spin of the black hole.

Bonus #1: how to become an astronomer. From ballerina to MIT to software engineer to astronomer. (Hanging out with astronomers makes you a worse software engineer).

Bonus #2: “Hubble hugger” John Grunsfeld stops by to talk about sun worshiping.

[this post originally appeared as a post on Wayne's Facebook wall]
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