Far out cosmology: bubbles surrounding the Milky way (Introduction)

by David Turell , Sunday, May 14, 2023, 16:08 (349 days ago) @ David Turell

Giant gas bubbles:

https://www.sciencealert.com/giant-bubbles-surrounding-the-milky-way-are-more-complex-t...

"Extending high above and below the Milky Way's galactic plane, a pair of huge, symmetrical blobs of gas stretch out like the lobes of a cosmic hourglass, glowing faintly with an X-ray radiance.

"They're known as eROSITA bubbles, named after the X-ray telescope that spotted them in 2020, and are located in the Milky Way's massive shell of gas, or 'circumgalactic medium', extending some 45,661 light-years either side of the galactic center.

"The energetic gasses making up the bubbles were assumed to have a fairly even, if somewhat high temperature throughout, caused by the shock of its passage through the medium. Though a surprising discovery now makes them seem more complex than first appears.

"Data from the Suzaku satellite, run by NASA and the Japanese Aerospace Exploration Agency (JAXA), suggests the X-ray glow of the bubbles isn't because they're hotter than their surrounds as assumed, but rather that the gasses simply have a higher density.

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"Previously, a temperature difference between the eROSITA bubbles and the surrounding galactic halo was assumed because of the relative brightness of the bubble shells. According to the newer method of analysis, that brightness is down to the higher density of the gas inside the bubbles and not heat.

"The research also sheds some light on how these bubbles formed: readings of non-solar ratios of neon-oxygen and magnesium-oxygen in the bubble shells suggest these bubbles were formed by nuclear star formation, or the injection of energy from other objects (like massive stars for example).

"It gives less credence to a previous hypothesis that a supermassive black hole and its associated activity – high-speed winds creating as objects are caught in the black hole's pull – are behind the creation of the eROSITA bubbles.

"'Our data supports the theory that these bubbles are most likely formed due to intense star formation activity at the galactic center, as opposed to black hole activity occurring at the galactic center," says astronomer Smita Mathur, from Ohio State University.

"It's thought that the eROSITA bubbles are connected to smaller but similarly shaped blobs of gas called Fermi bubbles, which were discovered in 2010 with NASA's gamma-ray telescope. Astronomers have suggested that the same events created all of these galactic bubbles, so the findings are relevant here too."

Comment: there is lots to learn about the Milky Way. We have no idea how much will apply to other spiral galaxies. Is the Milky Way ordinary or special?