IGR J17091-3624

Lore & Background

IGR J17091-3624 was discovered by ESA's INTEGRAL satellite in April 2003. It is a stellar mass black hole with a mass between 3 and 10 M☉, though as of 2017 its mass was described as 'unknown'. It is part of a binary system where a star orbits the black hole, and its small size may make it a candidate for the smallest black hole discovered.

Observations by the Chandra X-ray Observatory in 2011 revealed that IGR J17091 produces the fastest winds ever coming from an accretion disk, at 3,218,688 km/h (2 million mph), about 0.3% of the speed of light. This is 10 times faster than the next-highest-measured wind speed. According to Ashley King from the University of Michigan, 'Contrary to the popular perception of black holes pulling in all of the material that gets close, we estimate up to 95 percent of the matter in the disk around IGR J17091 is expelled by the wind.'

IGR J17091 also exhibits peculiar X-ray variability patterns or 'heartbeats'—small, quasi-periodic outbursts repeated over a 5- to 70-second timescale. Similar variability has only been observed in the black hole GRS 1915+105; however, IGR J17091's outbursts are 20 times fainter.

Reader's Guide

IGR J17091-3624 holds significance as a stellar mass black hole that challenges common perceptions of black hole behavior. Its discovery by ESA's INTEGRAL satellite in 2003 added to the catalog of known black holes in the Milky Way. The 2011 Chandra X-ray Observatory observations revealed that it produces the fastest winds ever measured from an accretion disk, at 3,218,688 km/h, which is about 0.3% of the speed of light and 10 times faster than any previously recorded wind from such a disk. This finding, along with the estimate that up to 95% of the matter in its accretion disk is expelled by the wind, provides insight into how black holes can influence their surroundings by ejecting material rather than solely accreting it. Additionally, its 'heartbeat' X-ray variability patterns—quasi-periodic outbursts on a 5- to 70-second timescale—are rare, having only been observed in one other black hole, GRS 1915+105, though IGR J17091's outbursts are 20 times fainter. These characteristics make IGR J17091 a valuable object for studying accretion physics and the dynamics of black hole systems. Its potential status as the smallest black hole discovered, despite the uncertainty in its mass as of 2017, further underscores its importance in astrophysical research.