StarXiv: a podcast discussing the latest astronomy papers
Apr 28, 2026 · 34 min · 17 segments
In this episode, Nicole and Payel discuss an accurate dating of the Gaia-Enceladus Sausage merger with the Milky Way, a new probe of matter clustering on small scales using Fast Radio Bursts, a new…
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Payel DasHostMichelle CollinsHostSo the first paper I'm going to talk about today is called The Last Galactic Firework: Timing the Last Significant Merger with Stars, Globular Clusters, and Omega Centauri.
And, uh, the authors of this were Sivan Mephite and Matthew Orkney from the Paris Observatory and the Universitat Barcelona.
And yeah, so jumping straight into this, judging by the, the title of Timing the Last Significant Merger, this is, of course, Gaia Enceladus for the Milky Way.
But, you know, obviously galaxies like the Milky Way form through hierarchical assembly, so the repeated mergers with small galaxies.
But observationally, when you look to the Milky Way's inner stellar halo, we find it to be dominated by debris from this one major event, which is Gaia Sausage Enceladus.
And previous work kind of looking at this system established that, A, it's the dominant contributor to the inner halo, and the timing of its merger is somewhere in the 8 to 12 gigayears range.
And so the core question of this paper is whether or not they can precisely date the Gaia Enceladus merger.
And so what's new about this paper, so it introduces a slightly new framework combining all of these different independent traces, so using stellar ages from subgiants to aged globular clusters, and also use dynamical signatures to try and build this single self-consistent timeline of when this merger took place.
And so what they did, as I said, they took these subgiant stars as their precise age traces.
So they used Milky Way subgiant stars using spectrophotometric ages, and this allowed them to create this tight age-metallicity relation which they could then measure.
And the idea here is that the youngest accreted stars from Gaia Enceladus can set the lower bound on your merger timeline.
And another thing is the authors identify a key feature in the Milky Way's kind of formation, which is the spin-up.
And so a lot of our listeners will kind of know this as the transition in stellar kinematics you see from having the halo-like random pressure-supported motion to disk-like, so having this ordered rotation, and this is kind of called the spin-up transition.
And previous studies imply that this spin-up is somewhat of a gradual formation of the galactic disk.
So the first paper I'm going to talk about today is called The Last Galactic Firework: Timing the Last Significant Merger with Stars, Globular Clusters, and Omega Centauri.
And, uh, the authors of this were Sivan Mephite and Matthew Orkney from the Paris Observatory and the Universitat Barcelona.
And yeah, so jumping straight into this, judging by the, the title of Timing the Last Significant Merger, this is, of course, Gaia Enceladus for the Milky Way.
But, you know, obviously galaxies like the Milky Way form through hierarchical assembly, so the repeated mergers with small galaxies.
But observationally, when you look to the Milky Way's inner stellar halo, we find it to be dominated by debris from this one major event, which is Gaia Sausage Enceladus.
And previous work kind of looking at this system established that, A, it's the dominant contributor to the inner halo, and the timing of its merger is somewhere in the 8 to 12 gigayears range.
And so the core question of this paper is whether or not they can precisely date the Gaia Enceladus merger.
And so what's new about this paper, so it introduces a slightly new framework combining all of these different independent traces, so using stellar ages from subgiants to aged globular clusters, and also use dynamical signatures to try and build this single self-consistent timeline of when this merger took place.
And so what they did, as I said, they took these subgiant stars as their precise age traces.
So they used Milky Way subgiant stars using spectrophotometric ages, and this allowed them to create this tight age-metallicity relation which they could then measure.
And the idea here is that the youngest accreted stars from Gaia Enceladus can set the lower bound on your merger timeline.
And another thing is the authors identify a key feature in the Milky Way's kind of formation, which is the spin-up.
And so a lot of our listeners will kind of know this as the transition in stellar kinematics you see from having the halo-like random pressure-supported motion to disk-like, so having this ordered rotation, and this is kind of called the spin-up transition.
And previous studies imply that this spin-up is somewhat of a gradual formation of the galactic disk.
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