Disk galaxies like the Milky Way form stars “inside-out” — starting from the center and working outwards through the disk. So, as a general rule, the farther out astronomers look, the younger the stars are.
Now, a team led by Karl Fiteni (then at University of Malta), carried out under the supervision of Joseph Caruana and Victor Debattista, has analyzed more than 100,000 giant stars. By coupling observations with advanced computer simulations, the astronomers show that this inside-out pattern reverses at between 35,000 and 40,000 light-years from the Milky Way’s center. Beyond this distance, the stars are older again.
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The analysis involves data from the LAMOST and APOGEE spectroscopic surveys, as well as measurements from the European Space Agency’s Gaia satellite. Fiteni’s team focused on red giant branch stars, whose ages can be estimated with relatively high precision. The results are published in Astronomy & Astrophysics.
The stars beyond this boundary probably weren’t formed in situ. But they didn’t come from infalling satellite galaxies either. Instead, they likely migrated outward over time. “A key point about the stars in the outer disk is that they are on close-to-circular orbits, meaning that they had to have formed in the disk,” says team member Victor Debattista (University of Lancashire, UK).
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Similar U-shaped age profiles have been seen in simulated disk galaxies and inferred in observations of other galaxies beyond our own. So the Milky Way is not unusual but merely following a common pattern of disk evolution, with the newly identified boundary marking a transition that may be a generic feature of spiral galaxies.
It is currently unclear what stymies star formation beyond this boundary. It is possible that the gravity of the Milky Way’s central bar corrals gas at preferred radii. Or it could be due to the bend of the galaxy, which warps towards the edge, disrupting star formation in the outer reaches.
New and future instruments could help paint a clearer picture. They include the 4MOST spectroscopic instrument at the European Southern Observatory in Chile, which saw first light last October, and the WEAVE spectrograph, attached to the William Herschel Telescope at La Palma in the Canary Islands.
I love science. I live my life based on science. But how can we really know how precise these estimates are? It's not like humanity has ever visited a "red giant branch star". I'd like to know the...
Fiteni’s team focused on red giant branch stars, whose ages can be estimated with relatively high precision
I love science. I live my life based on science. But how can we really know how precise these estimates are? It's not like humanity has ever visited a "red giant branch star". I'd like to know the precision of these estimates that are supposedly high precision.
They report an age uncertainty of 1.3 billion years for 66k stars and 1.1 billion years for another 36k, about a cool 10% of the age of the universe. If I'm skimming correctly, the juice here is...
They report an age uncertainty of 1.3 billion years for 66k stars and 1.1 billion years for another 36k, about a cool 10% of the age of the universe. If I'm skimming correctly, the juice here is using math for improving precision from a couple papers and applying it here to tease out this boundary. Figure 3 of the linked paper graphs age error distribution. Figure 6 has the age distributions. The pattern looks like one that could easily be lost in noisier data.
As for how we really know things... Well, we can do experiments here to learn the physics behind phenomena like light, we can do models to form a coherence between lab work, observations, and math, then apply that to situations where we can't directly observe and measure. But it isn't like a bridge -- get that wrong, it collapses, people get hurt. You can find the cause and either reinforce or improve the theory. That question, that difference, ate at me and was part of walking away from academia in planetary sciences, someone else surely has a more convincing answer.
My understanding is that relatively is a load-bearing word in that sentence. I assume that of all the different types of stars we’ve observed, some kinds we are more confident about estimating...
My understanding is that relatively is a load-bearing word in that sentence.
I assume that of all the different types of stars we’ve observed, some kinds we are more confident about estimating their age, and some kinds we are less confident. Therefore, if I was going to try to analyse lots of stars to build towards a conclusion like this, I would avoid using the star types that were less confident about, and instead use the stars that we’re more confident about.
And then if I was going to write this up in an article, I can see myself making the same shorthand of “relatively more precise”.
From the article:
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I love science. I live my life based on science. But how can we really know how precise these estimates are? It's not like humanity has ever visited a "red giant branch star". I'd like to know the precision of these estimates that are supposedly high precision.
They report an age uncertainty of 1.3 billion years for 66k stars and 1.1 billion years for another 36k, about a cool 10% of the age of the universe. If I'm skimming correctly, the juice here is using math for improving precision from a couple papers and applying it here to tease out this boundary. Figure 3 of the linked paper graphs age error distribution. Figure 6 has the age distributions. The pattern looks like one that could easily be lost in noisier data.
As for how we really know things... Well, we can do experiments here to learn the physics behind phenomena like light, we can do models to form a coherence between lab work, observations, and math, then apply that to situations where we can't directly observe and measure. But it isn't like a bridge -- get that wrong, it collapses, people get hurt. You can find the cause and either reinforce or improve the theory. That question, that difference, ate at me and was part of walking away from academia in planetary sciences, someone else surely has a more convincing answer.
My understanding is that relatively is a load-bearing word in that sentence.
I assume that of all the different types of stars we’ve observed, some kinds we are more confident about estimating their age, and some kinds we are less confident. Therefore, if I was going to try to analyse lots of stars to build towards a conclusion like this, I would avoid using the star types that were less confident about, and instead use the stars that we’re more confident about.
And then if I was going to write this up in an article, I can see myself making the same shorthand of “relatively more precise”.