The New Story of the Milky Way's Surprisingly Turbulent Past | Hacker News Reader

The New Story of the Milky Way's Surprisingly Turbulent Past

scientificamerican.com

35 pointspseudolus6 comments

For a good visualisation of the galactic evolution from the early universe, as well as the various intergalactic collisions described in this article, check out this video:

http://www.tng-project.org/movies/tng/tng50_single_galaxy_fo...

From the IllustrisTNG[1] cosmological simulation project:

> Formation of a single galaxy "g3", tracked through time from high redshift until the present day. This relatively "average" TNG50 galaxy will be just slightly less massive than our own Milky Way at z=0. We include a large-scale view (lower left), and zoomed in views of the central gas and stellar structures (lower right), while the main panel shows projected gas density. At z=1.5 we pause and rotate around the system, showing in order: gas metallicity, gas velocity field, and H-alpha luminosity, before continuing. What is a small dwarf at high redshift (108.3 solar masses in stars at z=4) transitions, at late times, into a large stable disk with a quasi-steady star formation rate of a few solar masses per year.

[1]: https://www.tng-project.org/about/

https://archive.ph/DOK5W

"Astronomers are making the first exact maps of the Milky Way: locations of stars in three dimensions..."

I thought that "standard candles" were required to estimate the distance to any region of space?

How can the distance to arbitrary stars be determined without these markers?

Gaia is orbiting around the L2 Lagrange point. As it traverses its orbit, the stars will appear to wiggle (relative to their previous recorded position) because of the stellar parallax effect. This (along with precisely knowing Gaia's orbit) enables scientists to accurately measure the distance to the star - if it wiggles more, it's closer. If it wiggles less, it's further away.

There is a limit to this method of measurement, based on the accuracy of the telescope. For Gaia:

> The European Space Agency's Gaia mission is expected to measure parallax angles to an accuracy of 10 microarcseconds for all moderately bright stars, thus mapping nearby stars (and potentially planets) up to a distance of tens of thousands of light-years from Earth.

The Milky Way is about 100,000 light-years wide. So it is able to accurately measure the distance for a _lot_ of stars around us in our galaxy.

This video probably explains it better: https://www.youtube.com/watch?v=Jdy09y0A4t0

To be clear (and the video isn't), the parallax is observed and calculated mostly from the diameter of Earth's orbit, with observations made six months apart. Gaia's L2 orbit is a much smaller factor, on the order of 1M km compared to Earth's orbital diameter of 300M km.

> Astronomers are making the first exact maps of the Milky Way: locations of stars in three dimensions

Maybe science fiction authors can stop making up locations entirely now.

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