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]


Cosmology—the study of the Universe as a whole—requires accurate measurements of the distances to galaxies and other objects billions of light-years away. However, the reliability of those estimates depends on how accurately we know the distance to closer objects, such as the Milky Way’s satellite galaxy known as the Large Magellanic Cloud (LMC). A new study has obtained the most accurate distance to the LMC yet, which in turn leads to better cosmological measurements. The key to the new distance measure: binary systems in the LMC consisting of two aging stars in relatively large orbits.

The researchers used data from the Optical Gravitational Lensing Experiment (yes, it’s nicknamed OGLE), which was designed to look for fluctuations in dark matter density by observing stars in the LMC. While OGLE hasn’t succeeded in its primary goal of spotting clumps of dark matter, it has amassed a lot of data from 35 million stars, going back as far as 1992.

From those 35 million stars, the astronomers identified 12 eclipsing binary stars; of those, they analyzed data from eight pairs for a period of eight years. These pairs they chose are rare, consisting of stars in the helium-burning stage, which occurs after they have exhausted their core’s hydrogen fuel. Aging stars of this type have well-known intrinsic brightness in relation to their color. [Read more…]

Aging binaries provide new calibration for cosmic distances