The observational properties of ultraluminous X-ray sources

Ultraluminous X-ray sources (ULXs) are extragalactic sources found in the off-nuclear regions of nearby galaxies with luminosities that appear to exceed the Eddington limit for a stellar mass black hole (BH). Historically, their extreme luminosities was interpreted as evidence that they host a population of accreting intermediate mass black holes (IMBHs), which are crucial to understand the formation of supermassive black holes in the early universe. However, this picture has changed in the past decade with the availability of high quality X-ray observations from XMM-Newton, Chandra and NuSTAR, which instead suggest that a majority of the known ULXs contain regular stellar mass compact objects that appear to break the Eddington limit (although a few interesting IMBH candidates remain). This picture is also strengthened by the recent discoveries of a few pulsating ULXs suggesting such objects contain neutron stars (NSs), although it is currently unclear how they may overcome their Eddington limit and if they are predominant among ULXs in comparison to black holes. In this talk, I will provide an overview of the astrophysical properties of ULXs, discuss some key results that have emerged in the recent years, including my work on the recent discovery of an ultra luminous X-ray pulsar. 

Zoom session details:
Meeting ID: 850 4491 0172 
Passcode: 996691