Some of the most massive galaxies contain predominantly old stars and form very few new ones, even when gas is available. Michael Blanton explains why feedback from accreting supermassive black holes is a leading explanation for suppressing that star formation. In conversation with Krishna Choudhary, he emphasizes that different simulations can reproduce the outcome through different mechanisms, leaving the detailed physical explanation unsettled.
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Gas must be able to cool and collect before it can form new stars.
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Energy associated with an active galactic nucleus can heat gas or drive it away, limiting the fuel available for star formation.
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Blanton distinguishes agreement with observed galaxy masses from establishing which feedback mechanism operates in nature.
435 words · auto-generated from the episode video
35:20Um and uh that problem, which existed in the '90s, is is still not, as far as I'm concerned, explained today. And that has consequences like those galaxies don't get as massive as your theoretical expectation would be. Now, there is a theory that is the that is sort of if there is a generally accepted theory, it would be this, which is that somehow the supermassive black holes that are accreting ma- matter at the centers of these very massive galaxies are preventing star formation from
36:02happening. >> Okay. >> And somehow >> Somehow. >> Somehow. And so so there are like you know at least half a dozen different numerical simulation methods where people incorporate this and successfully stop the stars from forming in these more most massive galaxies. All of the models work. >> Okay. they're all different. >> Okay, yeah, got it. >> So, they all start with there's a black hole at the center of the galaxy and and it's doing something and then they all do different things and then the end result is that they get the galaxies to have the right mass.
36:43>> Okay. >> Uh and but but the the the ways in which they do that in detail are all different. Okay. And uh and that to me is you know, I would like to know which of those answers is correct. >> Yeah. That's so interesting. Uh so, that seems counterintuitive. I mean, big galaxies should just have Yeah, cuz the Milky Way is forming stars, right? The Milky Way is not one of these. >> The Milky Way is probably is maybe 10 times less massive than >> Okay, than this size. Yeah. >> than than this happens, depending on exactly how you count. >> Um but uh but yeah, so the Milky Way is in this
37:24mass range where some some galaxies aren't forming stars, some are, and Milky Way's actually kind of in the middle. >> Mhm. >> Um but these guys it's like no one is forming stars in this >> It's very rare for for for them to be forming stars and and again you know, you need a lot of energy to stop the gas from flowing in and it's forming stars. You need to like heat it up or blow it out. You need a lot of energy. So, like people are like, these black holes, they can generate a lot of energy, which is a really good argument, but the exact way in which that happens is >> still a mystery. >> is still a mystery.
AstronomyAstrophysicsOpen DataCosmology