X-Ray Emission from the Arches Cluster
Friday, May 24, 2019
Science Update - A look at CfA discoveries from recent journals

The Arches cluster is a massive star cluster located in the Galactic Center region of our galaxy, about one hundred light-years from the galaxy's supermassive blackhole, SgrA*, and about twenty-five thousand light-years away from us. The cluster is the densest known star cluster in our galaxy: in a volume spanned by a radius equal to that between the Sun and its nearest neighbor star, the Arches would have about one hundred thousand stars. The cluster contains more than 160 hot young ("O-type") stars whose initial masses were more than twenty solar masses.

The first X-ray observation of the region around the Arches cluster with Chandra revealed it to have strong bright X-ray emission, characterized by a strong emission line of highly ionized iron. The hot emission around the cluster's core was attributed to the multiple collisions between the strong winds of its massive stars. Non-stellar emission from the rest of the cluster was thought to come from the gas being excited by external X-ray emission, perhaps from SgrA* itself, or else possibly from bombardment by cosmic rays. Between 2000 and 2013, X-ray observations of the Arches with the XMM-Newton X-ray satellite revealed a dramatic decline in the intensity of the X-ray emission by about 30%. The scientists argue that drop in the cluster X-ray emission was so abrupt that it is more likely have to resulted from a drop in reflection of a bright X-ray flare in Sgr A* rather than from in some abrupt change in the local conditions. CfA astronomer JaeSub Hong was a member of a team that used the NuSTAR and XMM-Newton X-ray satellites to understand the origin of the cluster's changing X-ray emission. Their spectral analysis of the iron emission leads them to conclude that the emission had two separate components and they suggest that two separate, bright flares of SgrA* were responsible for the emission peaks.


"Investigating the Origin of the Faint Non-Thermal Emission of the Arches Cluster Using the 2015–2016 NuSTAR and XMM–Newton X-ray Observations," Ekaterina Kuznetsova, Roman Krivonos, Maïca Clavel, Alexander Lutovinov, Dmitry Chernyshov, JaeSub Hong, Kaya Mori, Gabriele Ponti, John Tomsick, and Shuo Zhang, MNRAS 484, 1627, 2019.