title: A millisecond pulsar in a stellar triple system.
abstract: Gravitationally bound three-body systems have been studied for hundreds of years and are common in our Galaxy. They show complex orbital interactions, which can constrain the compositions, masses and interior structures of the bodies and test theories of gravity, if sufficiently precise measurements are available. A triple system containing a radio pulsar could provide such measurements, but the only previously known such system, PSR B1620-26 (refs 7, 8; with a millisecond pulsar, a white dwarf, and a planetary-mass object in an orbit of several decades), shows only weak interactions. Here we report precision timing and multiwavelength observations of PSR J0337+1715, a millisecond pulsar in a hierarchical triple system with two other stars. Strong gravitational interactions are apparent and provide the masses of the pulsar M[Symbol: see text](1.4378(13), where M[Symbol: see text]is the solar mass and the parentheses contain the uncertainty in the final decimal places) and the two white dwarf companions (0.19751(15)M[Symbol: see text] and 0.4101(3))M[Symbol: see text], as well as the inclinations of the orbits (both about 39.2°). The unexpectedly coplanar and nearly circular orbits indicate a complex and exotic evolutionary past that differs from those of known stellar systems. The gravitational field of the outer white dwarf strongly accelerates the inner binary containing the neutron star, and the system will thus provide an ideal laboratory in which to test the strong equivalence principle of general relativity.
authors.affiliation: National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, Virginia 22903-2475, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Ransom
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia V6T 1Z1, Canada.
authors.forename: I H
authors.initials: IH
authors.lastname: Stairs
authors.affiliation: 1] Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands [2] Department of Physics, McGill University, 3600 University Street, Montreal, Quebec H3A 2T8, Canada.
authors.forename: A M
authors.initials: AM
authors.lastname: Archibald
authors.affiliation: 1] Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands [2] Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: J W T
authors.initials: JW
authors.lastname: Hessels
authors.affiliation: 1] Physics Department, University of Wisconsin-Milwaukee, PO Box 413, Milwaukee, Wisconsin 53201, USA [2] Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, Wisconsin 53706-1582, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Kaplan
authors.affiliation: Department of Astronomy and Astrophysics, University of Toronto, 50 St George Street, Toronto, Ontario M5S 3H4, Canada.
authors.forename: M H
authors.initials: MH
authors.lastname: van Kerkwijk
authors.affiliation: 1] Department of Physics and Astronomy, West Virginia University, White Hall, Box 6315, Morgantown, West Virginia 26506-6315, USA [2] Physics and Astronomy Department, Western Kentucky University, 1906 College Heights Boulevard, Bowling Green, Kentucky 42101-1077, USA.
authors.forename: J
authors.initials: J
authors.lastname: Boyles
authors.affiliation: Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands.
authors.forename: A T
authors.initials: AT
authors.lastname: Deller
authors.affiliation: Center for Radiophysics and Space Research, Cornell University, 524 Space Sciences Building, Ithaca, New York 14853, USA.
authors.forename: S
authors.initials: S
authors.lastname: Chatterjee
authors.affiliation: Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, Wisconsin 53706-1582, USA.
authors.forename: A
authors.initials: A
authors.lastname: Schechtman-Rook
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia V6T 1Z1, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Berndsen
authors.affiliation: Department of Physics, McGill University, 3600 University Street, Montreal, Quebec H3A 2T8, Canada.
authors.forename: R S
authors.initials: RS
authors.lastname: Lynch
authors.affiliation: Department of Physics and Astronomy, West Virginia University, White Hall, Box 6315, Morgantown, West Virginia 26506-6315, USA.
authors.forename: D R
authors.initials: DR
authors.lastname: Lorimer
authors.affiliation: Department of Physics, McGill University, 3600 University Street, Montreal, Quebec H3A 2T8, Canada.
authors.forename: C
authors.initials: C
authors.lastname: Karako-Argaman
authors.affiliation: Department of Physics, McGill University, 3600 University Street, Montreal, Quebec H3A 2T8, Canada.
authors.forename: V M
authors.initials: VM
authors.lastname: Kaspi
authors.affiliation: 1] Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands [2] Astro Space Center of the Lebedev Physical Institute, 53 Leninskij Prospekt, Moscow 119991, Russia.
authors.forename: V I
authors.initials: VI
authors.lastname: Kondratiev
authors.affiliation: Department of Physics and Astronomy, West Virginia University, White Hall, Box 6315, Morgantown, West Virginia 26506-6315, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: McLaughlin
authors.affiliation: 1] Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands [2] Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: van Leeuwen
authors.affiliation: 1] National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, Virginia 22903-2475, USA [2] Department of Physics and Astronomy, West Virginia University, White Hall, Box 6315, Morgantown, West Virginia 26506-6315, USA.
authors.forename: R
authors.initials: R
authors.lastname: Rosen
authors.affiliation: 1] Eureka Scientific Inc., 2452 Delmer Street, Suite 100, Oakland, California 94602-3017, USA [2] Physics Department, New York University at Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates.
authors.forename: M S E
authors.initials: MS
authors.lastname: Roberts
authors.affiliation: 1] Department of Physics and Astronomy, University of Texas at Brownsville, One West University Boulevard, Brownsville, Texas 78520, USA [2] Physics and Astronomy Department, University of New Mexico, 1919 Lomas Boulevard NE, Albuquerque, New Mexico 87131-0001, USA.
authors.forename: K
authors.initials: K
authors.lastname: Stovall