A neutron star with 2.17 times the mass of our Sun crammed into a sphere 18.6 miles across has been observed 4,600 light years from Earth by astronomers using the Green Bank Telescope in Pocahontas County.
The high-density neutron star is the most massive ever detected, and approaches the theoretical maximum mass possible for a neutron star, according to the researchers who discovered it.
Neutron stars, the compressed remains of massive stars that have collapsed and exploded, are among the densest objects in the universe. A single chunk of neutron star the size of a sugar cube would weigh about 100 million tons on Earth, according to a release on the discovery by the Green Bank Observatory.
Neutron stars that emit radio waves from their magnetic poles, like the record-setting one detected with the Green Bank Telescope, are also known as pulsars. Some pulsars, like JO740+6620, the record-setter detected at Green Bank, spin with such phenomenal speed and regularity that astronomers can use them as the cosmic equivalent of an atomic clock.
Such precise timekeeping helps astronomers study the nature of space/time, measure the masses of stellar objects and advance the understanding of general relativity.
JO740+6620 orbits in a binary system, accompanied by a white dwarf — a collapsed low-mass star much smaller than the giant suns that produce neutron stars.
As the radio wave-emitting pulsar passes behind the white dwarf, a tiny delay in the arrival time of the radio pulses takes place, caused by gravity from the white dwarf slightly warping the space surrounding it, in accordance with Albert Einstein’s general theory of relativity.
Astronomers can use the amount of that delay to calculate the mass of the white dwarf. Once that mass is determined, a relatively straightforward process is used to identify the mass of the pulsar.
“The orientation of this binary star system created a fantastic cosmic laboratory,’” said Scott Ransom, an astronomer at NRAO and a co-author of a paper accepted for publication in Nature Astronomy. “Neutron stars have this tipping point where their interior densities get so extreme that the force of gravity overwhelms even the ability of neutrons to resist further collapse. Each ‘most massive’ neutron star we find brings us closer to identifying that tipping point, helping us understand the physics of matter at these mind-boggling densities.”
“Neutron stars are as mysterious as they are fascinating,” said Thankful Cromartie, a graduate student at the University of Virginia, a pre-doctoral fellow at the National Radio Astronomy Observatory in Charlottesville and the principal author of the paper. “These city-sized objects are essentially ginormous atomic nuclei. They are so massive that their interiors take on weird properties. Finding the maximum mass that physics and nature will allow can teach us a great deal about this otherwise inaccessible realm in astrophysics.”
In 2010, the Green Bank Telescope was used to identify what was then the largest neutron star ever observed — J1614-2230, located about 3,000 light years from Earth, and calculated to contain about twice the mass of our Sun.
The Green Bank observations were part of the research used in Cromartie’s doctoral thesis, which proposed observing the binary system at two key points in their mutual orbits to accurately measure the mass of JO740+6620.
Those observations also were part of a larger observing campaign known as NANOGrav, short for the North American Nanohertz Observatory for Gravitational Waves.
The Green Bank Observatory is supported by the National Science Foundation and is operated under cooperative agreement by Associated Universities Inc.