StarXiv: a podcast discussing the latest astronomy papers
Aug 18, 2026 · 31 min · 8 segments
Michelle and Nicole sit down to discuss the latest papers from the arXiv, including the discovery of a globular cluster stream outside the Milky Way, how disk clumps migrate to the centres of…
Michelle CollinsHostSo, um, my first paper is called Clump Migration in Disk Galaxies: Revisiting Chandrasekhar's Dynamical Friction, and this is authored by Pushpak Pandey and Kanak Saha from the Inter-University Centre for Astronomy and Astrophysics in India.
And this was... is going to be submitted to A&A, I believe.
And yeah, so basically right into it, the, the context here is that, you know, with our, you know, high-resolution observations that we get with HST, you know, JWST, have revealed that galaxies at kind of redshifts from about naught .5 to three are frequently kind of irregular and lumpy rather than nice and smooth, um, and can be dominated by these kind of kiloparsec-scale star-forming clumps-
... that can, you know, carry anywhere from 10 million to, like, a billion solar masses, so quite significant.
Yes.
And, and what we're finding is that smaller versions of the same structures turn up in nearby spirals as well.
And so this kind of says that disk fragmentation is this kind of recurring process rather than, like, a one-off feature kind of in the early universe.
So, you know, we need to care about it.
[laughs]
And so how these clumps form is kind of mostly understood, so from gravitational instability in a turbulent self-gravitating disk.
Uh, but the question is, is what happens with these clumps and kind of how important that is for galaxy evolution, and this is much less settled.
So the kind of standard picture has them spiraling inward, so there'll be, like, a radial migration merging into the center, and the idea is, is that it helps build the, the bulge, uh, helping to drive nuclear star formation and also possibly helping to feed the central black hole.
So a clump moving through the surrounding stars and dark matter will have kind of a drag, uh, caused by, like, this trailing overdensity behind it.
And so the gravity of that weight kind of acts as like this brake, which bleeds off your orbital energy and your angular momentum.
And the formula for this is Chandrasekhar's, which is from 1943, and it assumes a point mass perturber on this kind of circular orbit moving through, uh, an infinite homogenous stationary background with this kind of isotropic Maxwellian velocity distribution.
So this is very much like simple idealized scenario, and it kind of seems to work well for satellite galaxies and globular clusters.
But when you kind of have more of a galactic disk, um, it kind of satisfies none of these assumptions that we-
... would simplistically make.
So, um, my first paper is called Clump Migration in Disk Galaxies: Revisiting Chandrasekhar's Dynamical Friction, and this is authored by Pushpak Pandey and Kanak Saha from the Inter-University Centre for Astronomy and Astrophysics in India.
And this was... is going to be submitted to A&A, I believe.
And yeah, so basically right into it, the, the context here is that, you know, with our, you know, high-resolution observations that we get with HST, you know, JWST, have revealed that galaxies at kind of redshifts from about naught .5 to three are frequently kind of irregular and lumpy rather than nice and smooth, um, and can be dominated by these kind of kiloparsec-scale star-forming clumps-
... that can, you know, carry anywhere from 10 million to, like, a billion solar masses, so quite significant.
Yes.
And, and what we're finding is that smaller versions of the same structures turn up in nearby spirals as well.
And so this kind of says that disk fragmentation is this kind of recurring process rather than, like, a one-off feature kind of in the early universe.
So, you know, we need to care about it.
[laughs]
And so how these clumps form is kind of mostly understood, so from gravitational instability in a turbulent self-gravitating disk.
Uh, but the question is, is what happens with these clumps and kind of how important that is for galaxy evolution, and this is much less settled.
So the kind of standard picture has them spiraling inward, so there'll be, like, a radial migration merging into the center, and the idea is, is that it helps build the, the bulge, uh, helping to drive nuclear star formation and also possibly helping to feed the central black hole.
So a clump moving through the surrounding stars and dark matter will have kind of a drag, uh, caused by, like, this trailing overdensity behind it.
And so the gravity of that weight kind of acts as like this brake, which bleeds off your orbital energy and your angular momentum.
And the formula for this is Chandrasekhar's, which is from 1943, and it assumes a point mass perturber on this kind of circular orbit moving through, uh, an infinite homogenous stationary background with this kind of isotropic Maxwellian velocity distribution.
So this is very much like simple idealized scenario, and it kind of seems to work well for satellite galaxies and globular clusters.
But when you kind of have more of a galactic disk, um, it kind of satisfies none of these assumptions that we-
... would simplistically make.
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