Silvestru Posted June 11, 2018 Posted June 11, 2018 Really interesting discovery. Article is easy to follow so please have a look. https://arxiv.org/pdf/1806.02751.pdf Quote We report the discovery of the first likely black hole in a non-interacting binary system with a field red giant. We identified the bright rapidly-rotating giant 2M05215658+4359220 as a binary system with a massive unseen companion. Subsequent radial velocity measurements reveal a system with an orbital period of ' 83 days and near-zero eccentricity. The photometric variability period of the giant is consistent with the orbital period, indicative of star spots and tidal synchronization. Constraints on the giant’s mass and radius from its luminosity, surface gravity, and temperature imply an unseen companion with mass of 2.5 − 5.8 M, indicating a low-mass black hole or an exceedingly massive neutron star. Measurement of the astrometric binary motion by Gaia will further characterize the system. This discovery demonstrates the potential of massive spectroscopic surveys like APOGEE and all-sky, highcadence photometric surveys like ASAS-SN to revolutionize our understanding of the compact object mass function, and to test theories of binary star evolution and the supernova mechanism.
T. McGrath Posted June 12, 2018 Posted June 12, 2018 (edited) All they know for certain is that the red giant is being orbited by an unseen companion with a mass between 2.5 − 5.8 M☉. They are simply guessing that this object may be a black-hole. This unseen mass is within the Tolman-Oppenheimer-Volkoff limit, although it has been recently suggested that the maximum mass for a neutron star can only be 2.16 M☉. Another possibility that they have not considered is that this unseen mass may be a rapidly rotating and/or highly magnetic white dwarf. Recent discoveries have placed the maximum mass of white dwarfs well beyond Chandrasekhar limit of 1.44 M☉. New estimates of rapidly rotating and/or highly magnetic white dwarfs places their maximum mass between 2.3 and 2.8 M☉. Sources:Using Gravitational-Wave Observations and Quasi-Universal Relations to Constrain the Maximum Mass of Neutron Stars - The Astrophysical Journal Letters, Volume 852, Number 2, January 2018. (free preprint)Nearby Supernova Factory Observation of SN 2007if: First Total Mass Measurement of a Super-Chandrasekhar-Mass Progenitor - The Astrophyisical Journal, Volume 713, Number 2, March 2010 (free issue)Significantly Super-Chandrasekhar Limiting Mass White Dwarfs as Progenitors for Peculiar Over-Luminous Type Ia Supernovae - arXiv : 1509.09008, September 2015 Edited June 12, 2018 by T. McGrath
beecee Posted June 12, 2018 Posted June 12, 2018 6 minutes ago, T. McGrath said: All they know for certain is that the red giant is being orbited by an unseen companion with a mass between 2.5 − 5.8 M☉. They are simply guessing that this object may be a black-hole. This unseen mass is within the Tolman-Oppenheimer-Volkoff limit, although it has been recently suggested that the maximum mass for a neutron star can only be 2.16 M☉. Hi T McGrath.... Which seems to suggest that the equations used to calculate these upper limits are faulty/wrong, and/or the equations as is, are neglecting some as yet unknown or unseen "property" of the degenerate mass ? Quote Another possibility that they have not considered is that this unseen mass may be a rapidly rotating and/or highly magnetic white dwarf. But how would that remain as unseen? On 6/11/2018 at 6:11 PM, Silvestru said: Really interesting discovery. Article is easy to follow so please have a look. https://arxiv.org/pdf/1806.02751.pdf Certainly is...thanks.
T. McGrath Posted June 12, 2018 Posted June 12, 2018 Just now, beecee said: Hi T McGrath.... Which seems to suggest that the equations used to calculate these upper limits are faulty/wrong, and/or the equations as is, are neglecting some as yet unknown or unseen "property" of the degenerate mass ? But how would that remain as unseen? I would not say that the limits established by Chandrasekhar and Tolman-Oppenheimer-Volkoff were "wrong." Just not complete. I have absolutely no doubt that the maximum mass of a non-rotating, non-magnetic white dwarf is precisely as Chandrasekhar calculated it to be. Chandrasekhar did not take into consideration a rapidly rotating or a highly magnetic white dwarf when calculating the maximum mass of a white dwarf. Therefore, his answer is not "wrong," it just does not include all the possibilities. Compared to its red giant companion, any neutron star or white dwarf in an ~83-day orbit will be virtually invisible to us. We can obviously detect the mass of the object from its gravitational effects on its companion, which is what they did, but there is no way we would be able to "see" it. 1
Silvestru Posted June 14, 2018 Author Posted June 14, 2018 Hello T. McGrath, beecee, I actually wrote to the main author of this paper, Todd A. Thompson telling him that we have some additional questions , and he took the time to answer the below question. (I edited the below question just not to seem to rude ) On 12/06/2018 at 10:36 PM, T. McGrath said: All they know for certain is that the red giant is being orbited by an unseen companion with a mass between 2.5 − 5.8 M☉. They are simply guessing that this object may be a black-hole. This unseen mass is within the Tolman-Oppenheimer-Volkoff limit, although it has been recently suggested that the maximum mass for a neutron star can only be 2.16 M☉. Another possibility that they have not considered is that this unseen mass may be a rapidly rotating and/or highly magnetic white dwarf. Recent discoveries have placed the maximum mass of white dwarfs well beyond Chandrasekhar limit of 1.44 M☉. New estimates of rapidly rotating and/or highly magnetic white dwarfs places their maximum mass between 2.3 and 2.8 M☉. He wrote: Quote Thank you for your interest. The unseen object may be a neutron star or a black hole. There is some possibility it could be a double white dwarf (a triple system). I am skeptical that white dwarfs can be stabilized by rotation or magnetic fields above the Chandrasekhar limit for times long compared to the dynamical time. Best regards, Todd Todd A. Thompson Professor and Vice Chair Department of Astronomy Ohio State University 2
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