Paradigm shift in understanding the Galactic eROSITA Bubbles
  The magnificent bubbles at the Galactic center provide a great channel to
understand the effects of feedback on galaxy evolution. The newly discovered
eROSITA bubbles show enhanced X-ray emission from the shells around bubbles.
Previous works assumed that the X-ray emitting gas in the shells has a single
temperature component and that they trace the shock-heated lower-temperature
Galactic halo gas. Here we show that the thermal structure of the eROSITA
bubble shells is more complex. Using Suzaku observations we find with high
confidence that the X-ray emission from the shells is best described by a
two-temperature thermal model, one near Galaxy's virial temperature at $\rm kT
\approx 0.2 ~keV$ and the other at super-virial temperatures ranging between
$\rm kT = 0.4-1.1 ~keV$. Furthermore, we show that temperatures of the virial
and super-virial components are similar in the shells and in the ambient
medium, although the emission measures are significantly higher in the shells.
We argue that the X-ray bright eROSITA bubble shells are the signature of
compressed isothermal radiative shocks. The age of the bubbles is constrained
to $70$--$\rm 130~Myr$. This expansion timescale, as well as the observed
non-solar Ne/O and Mg/O ratios, favor the stellar feedback models for the
formation of the Galactic bubbles, settling a long-standing debate on the
origin of the Galactic bubbles.
