Simons: The Gaia Sausage -- Major Collision Changed the Milky Way Galaxy

[bystander]

The Gaia Sausage: The Major Collision that Changed the Milky Way Galaxy
Center for Computational Astrophysics | Simons Foundations | 2018 Jul 04

Sausage Galaxy: An impression of the encounter between the Milky Way galaxy and the smaller Sausage galaxy about 8 billion to 10 billion years ago. The record of this ancient encounter is still preserved in the velocities and chemistry of the stars. Credit: V. Belokurov (Cambridge, UK); based on image by ESO/Juan Carlos Muñoz

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An international team of astronomers has discovered an ancient and dramatic head-on collision between the Milky Way and a smaller object, dubbed the “Sausage” galaxy. The cosmic crash was a defining event in the early history of the Milky Way and reshaped the structure of our galaxy, fashioning both its inner bulge and its outer halo, the astronomers report in a series of new papers.

The astronomers propose that around 8 billion to 10 billion years ago, an unknown dwarf galaxy smashed into our own Milky Way. The dwarf did not survive the impact: It quickly fell apart, and the wreckage is now all around us.

“The collision ripped the dwarf to shreds, leaving its stars moving in very radial orbits” that are long and narrow like needles, said Vasily Belokurov of the University of Cambridge and the Center for Computational Astrophysics at the Flatiron Institute in New York City. The stars’ paths take them “very close to the center of our galaxy. This is a telltale sign that the dwarf galaxy came in on a really eccentric orbit and its fate was sealed.”

The new papers in the Monthly Notices of the Royal Astronomical Society, The Astrophysical Journal Letters and arXiv.org outline the salient features of this extraordinary event. Several of the papers were led by Cambridge graduate student GyuChul Myeong. He and colleagues used data from the European Space Agency’s Gaia satellite. This spacecraft has been mapping the stellar content of our galaxy, recording the journeys of stars as they travel through the Milky Way. Thanks to Gaia, astronomers now know the positions and trajectories of our celestial neighbors with unprecedented accuracy. ...

Co-Formation of the Galactic Disc and the Stellar Halo - V. Belokurov et al

• Monthly Notices of the RAS 478(1):611 (July 2018) DOI: 10.1093/mnras/sty982
  arXiv.org > astro-ph > arXiv:1802.03414 > 09 Feb 2018

Apocenter Pile-Up: Origin of the Stellar Halo Density Break - Alis J. Deason et al

• arXiv.org > astro-ph > arXiv:1805.10288 > 25 May 2018 (v1), 03 Jul 2018 (v2)

The Sausage Globular Clusters - G. C. Myeong et al

• arXiv.org > astro-ph > arXiv:1805.00453 > 01 May 2018 (v1), 02 Jul 2018 (v2)

The Milky Way Halo in Action Space - G. C. Myeong et al

• Astrophysical Journal Letters 856(2):L26 (2018 Apr 01) DOI: 10.3847/2041-8213/aab613
  arXiv.org > astro-ph > arXiv:1802.03351 > 09 Feb 2018 (v1), 28 Mar 2018 (v2)

Discovery of New Retrograde Substructures: The Shards of ω Centauri? - G. C. Myeong et al

• Monthly Notices of the RAS 478(4):5449 (Aug 2018) DOI: 10.1093/mnras/sty1403
  arXiv.org > astro-ph > arXiv:1804.07050 > 19 Apr 2018 (v1), 02 Jul 2018 (v3)