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Astron. Astrophys. 331, L29-L32 (1998)

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Letter to the Editor

On the initial progenitor masses of stellar mass black holes and neutron stars

small.htm E. Ergma * 1, 2 and E.P.J. van den Heuvel 2, 3

1 Physics Department, Tartu University, Ulikooli 18, EE-2400 Tartu, Estonia
2 Astronomical Institute "Anton Pannekoek" Kruislaan 403, 1098, SJ Amsterdam, The Netherlands
3 Institute for Theoretical Physics UCSB, Santa Barbara, California 93106-4030, USA

Received 14 September 1997 / Accepted 21 November 1997


We examine the information on the progenitor masses of stellar black holes that can be derived from the seven known black hole X-ray binaries with low- mass donor stars (Soft X-ray Transients- SXRs) in combination with stellar evolution considerations and observed properties of High Mass X-ray Binaries (HMXBs). It appears that several independent lines of evidence indicate that a considerable fraction of the stars more massive than 20 - 25 [FORMULA] leave black holes as remnants while, on the other hand, t e neutron star in at least one HMXB had a progenitor more massive than 50 [FORMULA]. We argue that the only plausible explanation of these apparently contradicting facts is that in a certain mass range, probably between 20 and 50 [FORMULA], the outcome of core collapse can either be a neutron star or the black hole, depending on additional stellar parameters, for example rotation and magnetic fields.

The high masses of the black holes in three soft X-ray Transients (6 - 13 [FORMULA]) and Cygnus X-1 (16 [FORMULA]) exclude the alternative explanation that in a limited mass range (e.g.20 - 40 [FORMULA]) stars leave black holes, and, due to very heavy stellar wind mass loss, stars more massive than about 40 [FORMULA] leave neutron stars, just as stars between 8 and 20 [FORMULA].

Key words: Black holes - neutron stars - stellar evolution - Black Hole mass limit - X-ray Binaries - Soft X-ray Transients

* Correspondence and requests for materials to ene@physic.ut.ee

© European Southern Observatory (ESO) 1998

Online publication: February 16, 1998