I have a bit of time on my hands, so let's do another 24h round of #AskAnAstrophysicist, but this time it's a thematic one.
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I have a bit of time on my hands, so let's do another 24h round of #AskAnAstrophysicist, but this time it's a thematic one.
What do you want to ask an astrophysicist about stars? (I am a professional astrophysicist, part of whose work concerns itself with high mass stars & their winds and I've also taught a variety of astro university courses)
Boosts welcome. I may not be able to reply to all in case of many questions.
@vicgrinberg I've always thought the ability of gas & plasma to sustain shockwaves means they can actually carry sound.
one of the more spectacular examples would be the "bounce" of core collapse in a supernova. but years and years after that, the shockwave is still travelling and the gas density is very thin.
does that mean these thin clouds of gas can carry sound? are the remnants dense enough to carry it? your work is with stellar winds, does it have sound? does a corona carry sound? the gas "leak" from a cataclysmic variable, what about that...
(I am not a professional astrophysicist, but I sure wanted to be one.)
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I have a bit of time on my hands, so let's do another 24h round of #AskAnAstrophysicist, but this time it's a thematic one.
What do you want to ask an astrophysicist about stars? (I am a professional astrophysicist, part of whose work concerns itself with high mass stars & their winds and I've also taught a variety of astro university courses)
Boosts welcome. I may not be able to reply to all in case of many questions.
@vicgrinberg I know this may go unnoticed. Which is fine. Totally fine. At least I'm willing to try. Anyways, this is how I describe the physics of the Milky Way galaxy in the natural Universe. Is this:
Galaxies hold shape and rotation due to the Tropic Field Extremum's gravitational entrainment upon the stellar mass that is stabilized by the angular momentum trajectory of the host galaxy.
**Tropic Field Extremum**: is the gravitational "bowl" (not) a singularity. Like a skate bowl at a park. -
@Enema_Cowboy likely yes - but it's not that simple, eg NASA's Juno found that Jupiter core is rather "fuzzy" and not just a ball of heavy elements https://science.nasa.gov/jupiter/jupiter-facts/
@vicgrinberg Wow, I'm amazed that the structure of core could be detected.
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I have a bit of time on my hands, so let's do another 24h round of #AskAnAstrophysicist, but this time it's a thematic one.
What do you want to ask an astrophysicist about stars? (I am a professional astrophysicist, part of whose work concerns itself with high mass stars & their winds and I've also taught a variety of astro university courses)
Boosts welcome. I may not be able to reply to all in case of many questions.
I heard Brian Cox talk about “escape velocity” in relation to density. What are the densest objects discovered and how dense are they?
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I have a bit of time on my hands, so let's do another 24h round of #AskAnAstrophysicist, but this time it's a thematic one.
What do you want to ask an astrophysicist about stars? (I am a professional astrophysicist, part of whose work concerns itself with high mass stars & their winds and I've also taught a variety of astro university courses)
Boosts welcome. I may not be able to reply to all in case of many questions.
@vicgrinberg Perhaps more a quantum physics question than astrophysics, but: I never understood why fusion stops releasing energy at iron, and you start to need more energy than you get out if you fuse nuclei together above that weight.
The star lifecycle explanations I've run across in the past don't go deeper than "it just does", but is there a deeper reason?
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I have a bit of time on my hands, so let's do another 24h round of #AskAnAstrophysicist, but this time it's a thematic one.
What do you want to ask an astrophysicist about stars? (I am a professional astrophysicist, part of whose work concerns itself with high mass stars & their winds and I've also taught a variety of astro university courses)
Boosts welcome. I may not be able to reply to all in case of many questions.
@vicgrinberg
Bussard ramjets still impossible?
Solar sails possible? -
I have a bit of time on my hands, so let's do another 24h round of #AskAnAstrophysicist, but this time it's a thematic one.
What do you want to ask an astrophysicist about stars? (I am a professional astrophysicist, part of whose work concerns itself with high mass stars & their winds and I've also taught a variety of astro university courses)
Boosts welcome. I may not be able to reply to all in case of many questions.
@vicgrinberg
This could be a question specific to stars (or even specific to massive stars) or it could be a question for all of astrophysics, I guess. Are we collecting data about the universe and its. contents faster than we (meaning you astrophysicists primarily) can analyze it? I know there are citizen science projects that help to classify galaxies and whatnot (Galaxy Zoo? I don't remember) but I imagine the flood of data far outstrips the ability of humans to parse it all. True? Are we getting ever further behind? -
@vicgrinberg Perhaps more a quantum physics question than astrophysics, but: I never understood why fusion stops releasing energy at iron, and you start to need more energy than you get out if you fuse nuclei together above that weight.
The star lifecycle explanations I've run across in the past don't go deeper than "it just does", but is there a deeper reason?
@Two9A to be honest, I don't know what you mean by a deeper reason here. There is no reason why things are the way they are - except that we would not exist as we are if they weren't.
For atoms, you can roughly imagine that the more (positivly charged) protons there are, the harder it is to squeeze them together. So the larger the atom, the less energy is left over to be released when it is created, until at some point you need go add energy to make them instewd of releasing.
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I heard Brian Cox talk about “escape velocity” in relation to density. What are the densest objects discovered and how dense are they?
@DaveNelson it's not a about stars, but I'll answer (I like neutron stars & black holes): the densest objects of normal matter are neutron stars - pretty much the density of an atomic nucleus but as a star or the mass of 1.4 suns squeezed into a ball of 10 km radius. Denser doesn't work - if we pile up more than 3 sun masses together at neutron star density or squeeze the neutron star further, we end up with a black hole, where things collapse to endless density in a singularity in the middle.
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@vicgrinberg I've always thought the ability of gas & plasma to sustain shockwaves means they can actually carry sound.
one of the more spectacular examples would be the "bounce" of core collapse in a supernova. but years and years after that, the shockwave is still travelling and the gas density is very thin.
does that mean these thin clouds of gas can carry sound? are the remnants dense enough to carry it? your work is with stellar winds, does it have sound? does a corona carry sound? the gas "leak" from a cataclysmic variable, what about that...
(I am not a professional astrophysicist, but I sure wanted to be one.)
@draNgNon this is not a question about stats, so very short answer: gas clouds are far too thin to carry sound in the meaning of the sound on Earth - the densest gas clouds are as dense as some of the most extreme vacuums we can create on Earth. The Universe is very, very empty.
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I have a bit of time on my hands, so let's do another 24h round of #AskAnAstrophysicist, but this time it's a thematic one.
What do you want to ask an astrophysicist about stars? (I am a professional astrophysicist, part of whose work concerns itself with high mass stars & their winds and I've also taught a variety of astro university courses)
Boosts welcome. I may not be able to reply to all in case of many questions.
@vicgrinberg Do you think it is possible to verify models in theoretical physics using publicly available data from repositories such as https://researchguides.gonzaga.edu/physics/data only ? Just order this data around some N real world physical experiments and check your theoretical physics model for each of the N experiments. My idea is developing new models in theoretical physics using AI (new geometries in general relativity for example) and check them against the public data repos.
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@Two9A to be honest, I don't know what you mean by a deeper reason here. There is no reason why things are the way they are - except that we would not exist as we are if they weren't.
For atoms, you can roughly imagine that the more (positivly charged) protons there are, the harder it is to squeeze them together. So the larger the atom, the less energy is left over to be released when it is created, until at some point you need go add energy to make them instewd of releasing.
@vicgrinberg Fair, I guess it's a question along the lines of "what if G had a different value": not something one can answer except with "in this universe it doesn't".
Thanks for taking the time!
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Since I have not seen the question already: What are those winds you mentioned? How can I imagine them? I suspect stars don't have an atmosphere like planets do.
I am so confused.
@palaress ah, thanks for the question! Stellar wind (our Sun also has a wind, called solar wind) is not something that happens in an atmosphere, but rather a thin stream of particles blown away from the star from its uppermost layers. Stellar wind is what makes Aurorae (when there is an especially strong bit of it) and that makes comets have nice tails (the tail is pretty mucbtan interaction result of the comet with the wind).
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@vicgrinberg Do you think it is possible to verify models in theoretical physics using publicly available data from repositories such as https://researchguides.gonzaga.edu/physics/data only ? Just order this data around some N real world physical experiments and check your theoretical physics model for each of the N experiments. My idea is developing new models in theoretical physics using AI (new geometries in general relativity for example) and check them against the public data repos.
@liklyhood not a question about stars and no. Physics is not something done by single with help of AI. And you need to really understand you data to compare it with models, just getting it from online repos isn't enough. I know you will not listen, but I want others to read this. No.
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@coleenwalter it's a very cool question actually! The stars move relative to the solar system and the solar system itself moves through our galaxy, so overall the position of stars changes. The timescales are very large, though, so "just" a few thousand years ago things would not look too different, possibly not even noticeable with the nakes eye. But the further in the past you go (to pre homo sapiens time), the more different it would look - same for far away future!
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I have a bit of time on my hands, so let's do another 24h round of #AskAnAstrophysicist, but this time it's a thematic one.
What do you want to ask an astrophysicist about stars? (I am a professional astrophysicist, part of whose work concerns itself with high mass stars & their winds and I've also taught a variety of astro university courses)
Boosts welcome. I may not be able to reply to all in case of many questions.
@vicgrinberg So on 12 May 2026 at around 2000 hours to 2100 hours (GMT+5), I observed a star/celestial object in the sky which was way too on low down the horizon line and I think it was somewhere in the West (cos it was in the opposite direction where the sun rise). The geographical co-ordinates of my city are 24.860966° N and the longitude is 66.990501° E.
From where can I learn more about what it is/was ?! I don't know if this might sound like a stupid noob question but it's been bugging me
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@vicgrinberg @johnnythan This XKCD is more accurate than one might think. I've been guilty of it too.
@internic @johnnythan ah yes, xkcd forever
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@vicgrinberg @bkahn Interesting! So how do we know that these black holes were caused by single supermassive stars rather than having grown over time?
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@vicgrinberg Thanks Dr. Grinberg. Enjoy your vacation.
@GranVegas thank you
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@glc xkcd always wins
