Far out cosmology: the unusual Milky Way (Introduction)

by David Turell , Wednesday, November 27, 2024, 18:48 (3 hours, 55 minutes ago) @ David Turell

A new study:

https://www.sciencealert.com/giant-study-confirms-the-milky-way-really-is-an-unusual-ga...

"...new research that examines 101 of the Milky Way's kin shows how it differs from them.

"One powerful way to understand things is to compare and contrast them with others in their class, a technique we learn in school. Surveys are an effective tool to compare and contrast things, and astronomical surveys have contributed an enormous amount of foundational data towards the effort.

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"The studies are all based on 101 galaxies similar in mass to the Milky Way, and each study tackles a different aspect of comparing those galaxies to ours.

"The SAGA Survey. III. A Census of 101 Satellite Systems around Milky Way–mass Galaxies
The SAGA Survey. IV. The Star Formation Properties of 101 Satellite Systems around Milky Way–mass Galaxies

The SAGA Survey. V. Modeling Satellite Systems around Milky Way–Mass Galaxies with Updated Universe Machine

"Research shows that galaxies form inside gigantic haloes of dark matter, the elusive substance that doesn't interact with light. 85% of the Universe's matter is mysterious dark matter, while only 15% is normal or baryonic matter, the type that makes up planets, stars, and galaxies.

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"The comparison between the Milky Way and the 101 others revealed some significant differences.

"'Our results show that we cannot constrain models of galaxy formation just to the Milky Way," said Wechsler, who is also professor of particle physics and astrophysics at the SLAC National Accelerator Laboratory.

"'We have to look at that full distribution of similar galaxies across the universe."

"The SAGA Survey's third data release includes 378 satellites found in 101 MW-mass systems, and the first paper focuses on the satellites.

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"SAGA found that the number of satellites per galaxy ranges from zero to 13. According to the first paper, the mass of the most massive satellite is a strong predictor of the abundance of satellites.

"One-third of the SAGA systems contain LMC-mass satellites, and they tend to have more satellites than the MW," the paper states. The Milky Way is an outlier in this regard, which is one reason it's atypical.

"The second study focuses on star formation in the satellites. The star formation rate (SFR) is an important metric in understanding galaxy evolution.

"The research shows that star formation is still active in the satellite galaxies, but the closer they are to the host, the slower their SFR. Is it possible that the greater pull of the dark matter halo close to the galaxy is quenching star formation?

"Our results suggest that lower-mass satellites and satellites inside 100 kpc are more efficiently quenched in a Milky Way–like environment, with these processes acting sufficiently slowly to preserve a population of star-forming satellites at all stellar masses and projected radii," the second paper states.

"However, in the Milky Way's satellites, only the Magellanic Clouds are still forming stars, with radial distance playing a role.

"'Now we have a puzzle," Wechsler said.

"'What in the Milky Way caused these small, lower-mass satellites to have their star formation quenched? Perhaps, unlike a typical host galaxy, the Milky Way has a unique combination of older satellites that have ceased star formation and newer, active ones – the LMC and SMC – that only recently fell into the Milky Way's dark matter halo.'"

"This is another reason that our galaxy is atypical."

Comment: this is another study showing the Milky Way is very unusual. I think it is because we are here protected by God.