The gravitational waltz of the Milky Way’s satellites

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I’ve started contributing to the Forbes Science page again! This is my first new contribution, relating to the second data release from the Gaia survey telescope. (And if I can be shameless: Forbes pays according to traffic, so the more of you who share and visit and read my stuff, the better they pay me. Ahem.)

Plotting The Three-Dimensional Dance Of Galaxies

A map of the Milky Way’s satellite galaxies, globular clusters, and other objects in orbit. [Credit: ESA/Gaia]

For Forbes:

The European Space Agency’s Gaia telescope is designed to map the position and speed of a billion stars in the Milky Way and its neighboring galaxies. In fact, some of those galaxies are satellites, which whirl around our home galaxy in a complicated dance. Part of Gaia’s mission is to help us understand that dance.

Many of these satellite galaxies actually orbit inside the halo of the mysterious, invisible dark matter that makes up most of the Milky Way’s mass. For that reason, the dance of the satellites tells us about the structure of the Milky Way, along with the shared history and evolution of all the galaxies involved. The Gaia space telescope’s second data release from last week allowed astronomers to map out the positions and motion of stars inside eleven satellite galaxies, along with other star clusters. The result: new estimate on the mass of the Milky Way, and a fully three-dimensional map of nearly 90 objects in orbit around our galaxy.

[Read the rest at Forbes]


Do newer stars in globular clusters die before they get old?

According to theories of star life cycles, when a typical star exhausts its hydrogen fuel, it goes through a set of end-life stages before expiring, expanding and contracting over time. However, a new analysis of a globular cluster orbiting the Milky Way found that the younger generation of stars didn’t seem to reach the later stage of life known as the asymptotic giant branch phase. The astronomers conducting the study discovered this by looking for emission from sodium atoms in stellar atmospheres; since the older generation of stars has far less sodium than the younger generation, its presence is a marker of when a given star formed. None of the asymptotic giant stars in the globular cluster had the expected sodium emission, meaning that something weird was happening.

However, a new observation of one of the Milky Way’s globular clusters turned up a problem: the younger generation of stars in the cluster didn’t seem to be passing through the asymptotic giant phase. Simon W. Campbell and colleagues found that while the red giant star population included stars from both older and younger populations, the asymptotic giant stars only represented the older generation. That’s in strong contradiction to theory: the era of a star’s formation shouldn’t affect its life cycle. The reason for this deviation is mysterious. [Read more…]

The headline to the Ars Technica story, alas, is misleading. There’s no reason to think the younger stars are living longer; in fact, it’s likely those stars are burning out sooner than expected for some unknown reason, unless there’s a way they’ve found to destroy or mask the sodium in their atmospheres.