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An unusually massive stellar black hole in the Galaxy
The X-ray source known as GRS1915+105 belongs to a group dubbed`microquasars'. These objects are binary systems which sporadicallyeject matter at speeds that appear superluminal, as is the case for somequasars. GRS1915+105 is also one of only two known binary sourcesthought to contain a maximally spinning black hole. Determining thebasic parameters of GRS195+105, such as the masses of the components,will help us to understand jet formation in this system, as well asproviding links to other objects which exhibit jets. Using X-ray data,indirect methods have previously been used to infer a variety of massesfor the accreting compact object in the range 10-30 solar masses(Mȯ). Here we report a direct measurement of theorbital period and mass function of GRS1915+105, which allow us todeduce a mass of 14 +/- 4Mȯ for the black hole. Blackholes with masses >5-7Mȯ challenge theconventional picture of black-hole formation in binary systems. Based onthe mass estimate, we interpret the distinct X-ray variability ofGRS1915+105 as arising from instabilities in an accretion disk that isdominated by radiation pressure, and radiating near the Eddington limit(the point where radiation pressure supports matter against gravity).Also, the mass estimate constrains most models which relate observableX-ray properties to the spin of black holes in microquasars.
| Identification of the donor in GRS 1915+105
We report on medium-resolution H and K band spectroscopy of GRS 1915+105using the 8m VLT at ESO. We clearly identify absorption bandheads from^12CO/^13CO. Together with other features we classify the donor as a K-MIII star.
| Identification of the donor in the X-ray binary GRS 1915+105
We report on the results of medium-resolution spectroscopy of GRS1915+105 in the near-infrared H and K band using the 8 m VLT at ESO. Weclearly identify absorption bandheads from 12CO and13CO. Together with other features this results in aclassification of the mass-donating star in this binary as a K-M IIIstar, clearly indicating that GRS 1915+105 belongs to the class oflow-mass X-ray binaries (LMXB). Based on observations collected at theEuropean Southern Observatory, Chile under proposals ESO Nos. 63.H-0465and 65.H-0422.
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