A huge reservoir of ionized gas around the Milky Way: Accounting for the Missing Mass?

TL;DR

This study reveals a massive, hot ionized gas reservoir around the Milky Way, potentially accounting for the galaxy's missing baryonic mass, through X-ray observations of the circumgalactic medium.

Contribution

It provides the first direct measurement of the hot, ionized gas phase of the Milky Way's circumgalactic medium using X-ray data, highlighting its significant mass.

Findings

The hot gas extends over 100 kpc around the Milky Way.

The mass of this hot gas exceeds ten billion solar masses.

This hot phase likely accounts for the galaxy's missing baryonic mass.

Abstract

Most of the baryons from galaxies have been "missing" and several studies have attempted to map the circumgalactic medium (CGM) of galaxies in their quest. Recent studies with the Hubble Space Telescope have shown that many galaxies contain a large reservoir of ionized gas with temperatures of about 10^5 K. Here we report on X-ray observations made with the Chandra X-ray Observatory probing an even hotter phase of the CGM of our Milky Way at about 10^6 K. We show that this phase of the CGM is massive, extending over a large region around the Milky Way, with a radius of over 100 kpc. The mass content of this phase is over ten billion solar masses, many times more than that in cooler gas phases and comparable to the total baryonic mass in the disk of the Galaxy. The missing mass of the Galaxy appears to be in this warm-hot gas phase.