A $1.9\,M_{\odot}$ neutron star candidate in a 2-year orbit
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| Format: | Preprint |
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2024
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| author | El-Badry, Kareem Simon, Joshua D. Reggiani, Henrique Rix, Hans-Walter Latham, David W. Bieryla, Allyson Buchhave, Lars A. Shahaf, Sahar Mazeh, Tsevi Chakrabarti, Sukanya Guhathakurta, Puragra Ilyin, Ilya V. Tauris, Thomas M. |
| author_facet | El-Badry, Kareem Simon, Joshua D. Reggiani, Henrique Rix, Hans-Walter Latham, David W. Bieryla, Allyson Buchhave, Lars A. Shahaf, Sahar Mazeh, Tsevi Chakrabarti, Sukanya Guhathakurta, Puragra Ilyin, Ilya V. Tauris, Thomas M. |
| contents | We report discovery and characterization of a main-sequence G star orbiting a dark object with mass $1.90\pm 0.04 M_{\odot}$. The system was discovered via Gaia astrometry and has an orbital period of 731 days. We obtained multi-epoch RV follow-up over a period of 639 days, allowing us to refine the Gaia orbital solution and precisely constrain the masses of both components. The luminous star is a $\gtrsim 12$ Gyr-old, low-metallicity halo star near the main-sequence turnoff ($T_{\rm eff}\approx 6000$ K; $\log(g/\left[{\rm cm\,s^{-2}}\right])\approx 4.0$; $\rm [Fe/H]\approx-1.25$; $M\approx0.79 M_{\odot}$) with a highly enhanced lithium abundance. The RV mass function sets a minimum companion mass for an edge-on orbit of $M_2 > 1.67 M_{\odot}$, well above the Chandrasekhar limit. The Gaia inclination constraint, $i=68.7\pm 1.4$ deg, then implies a companion mass of $M_2=1.90\pm0.04 M_{\odot}$. The companion is most likely a massive neutron star: the only viable alternative is two massive white dwarfs in a close binary, but this scenario is disfavored on evolutionary grounds. The system's low eccentricity ($e=0.122\pm 0.002$) disfavors dynamical formation channels and implies that the neutron star likely formed with little mass loss ($\lesssim1\,M_{\odot}$) and with a weak natal kick ($v_{\rm kick}\lesssim 20\,\rm km\,s^{-1}$). The current orbit is too small to have accommodated the neutron star progenitor as a red supergiant or super-AGB star. The simplest formation scenario -- isolated binary evolution -- requires the system to have survived unstable mass transfer and common envelope evolution with a donor-to-accretor mass ratio $>10$. The system, which we call Gaia NS1, is likely a progenitor of symbiotic X-ray binaries and long-period millisecond pulsars. Its discovery challenges binary evolution models and bodes well for Gaia's census of compact objects in wide binaries. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2402_06722 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | A $1.9\,M_{\odot}$ neutron star candidate in a 2-year orbit El-Badry, Kareem Simon, Joshua D. Reggiani, Henrique Rix, Hans-Walter Latham, David W. Bieryla, Allyson Buchhave, Lars A. Shahaf, Sahar Mazeh, Tsevi Chakrabarti, Sukanya Guhathakurta, Puragra Ilyin, Ilya V. Tauris, Thomas M. Solar and Stellar Astrophysics We report discovery and characterization of a main-sequence G star orbiting a dark object with mass $1.90\pm 0.04 M_{\odot}$. The system was discovered via Gaia astrometry and has an orbital period of 731 days. We obtained multi-epoch RV follow-up over a period of 639 days, allowing us to refine the Gaia orbital solution and precisely constrain the masses of both components. The luminous star is a $\gtrsim 12$ Gyr-old, low-metallicity halo star near the main-sequence turnoff ($T_{\rm eff}\approx 6000$ K; $\log(g/\left[{\rm cm\,s^{-2}}\right])\approx 4.0$; $\rm [Fe/H]\approx-1.25$; $M\approx0.79 M_{\odot}$) with a highly enhanced lithium abundance. The RV mass function sets a minimum companion mass for an edge-on orbit of $M_2 > 1.67 M_{\odot}$, well above the Chandrasekhar limit. The Gaia inclination constraint, $i=68.7\pm 1.4$ deg, then implies a companion mass of $M_2=1.90\pm0.04 M_{\odot}$. The companion is most likely a massive neutron star: the only viable alternative is two massive white dwarfs in a close binary, but this scenario is disfavored on evolutionary grounds. The system's low eccentricity ($e=0.122\pm 0.002$) disfavors dynamical formation channels and implies that the neutron star likely formed with little mass loss ($\lesssim1\,M_{\odot}$) and with a weak natal kick ($v_{\rm kick}\lesssim 20\,\rm km\,s^{-1}$). The current orbit is too small to have accommodated the neutron star progenitor as a red supergiant or super-AGB star. The simplest formation scenario -- isolated binary evolution -- requires the system to have survived unstable mass transfer and common envelope evolution with a donor-to-accretor mass ratio $>10$. The system, which we call Gaia NS1, is likely a progenitor of symbiotic X-ray binaries and long-period millisecond pulsars. Its discovery challenges binary evolution models and bodes well for Gaia's census of compact objects in wide binaries. |
| title | A $1.9\,M_{\odot}$ neutron star candidate in a 2-year orbit |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2402.06722 |