- American Physical Society Sites
- Meetings & Events
- Policy & Advocacy
- Careers In Physics
- About APS
- Become a Member
The nature of ultraluminous X-ray sources remains controversial, but many astronomers think that some or most of these objects consist of an intermediate-mass black hole that accretes matter from a companion star. Recent evidence suggests that a ULX in the galaxy NGC 5408 has a black hole with about 2,000 solar masses.
See related news release: NASA scientists pioneer technique for 'weighing' black holes.