A massive neutron star only 30 kilometers across but with a mass 2.17 times that of the Sun has been discovered 4,600 light years away from Earth. MSP J0740+6620 is therefore the most massive neutron star ever detected, beating the last record holder which had a mass equivalent to 2.01 sol.
The startling discovery was made by astronomers from the Green Bank Observatory in West Virginia, who said that its mass was close to limit after which it would be crushed into a black hole. Commenting upon the finding, Scott Ransom, an astronomer at the National Radio Astronomy Observatory (NRAO) who coauthored the paper published in the journal Nature, stated:
“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 and helping us to understand the physics of matter at these mind-boggling densities.”
Neutron Stars and Pulsars
After a massive star (10-29 sol) goes supernova, gravitational forces compress the remaining ultra-dense core of material past the white dwarf stage to form a neutron star. Those neutron stars which then rapidly-rotate are known as pulsars, and emit beams of radio waves from their two magnetic poles across space. The recently discovered MSP J0740+6620 also falls into the pulsar category, and is spinning at a rate of 289 times a second.
White Dwarf Companion and Shapiro Delay
MSP J0740+6620 is a binary system and has a white dwarf companion orbiting it. Scientists measuring the radio waves emitted by the pulsar subsequently noted a time delay in receiving the signal due to its companion passing in front of it. This effect known as “Shapiro Delay” has helped scientists to more accurately calculate the mass of MSP J0740+6620, as well as its white dwarf companion.
Tipping Point at which Black Hole Created?
Neutron stars are the densest ‘normal’ objects known to astrophysicists. Of course, black holes are even denser, but they are certainly far from normal. In fact, scientists believe that the strongest material in the Universe, referred to as “nuclear pasta,” can be found deep inside the crust of neutron stars.
The recent finding therefore helps scientists chip away at some of the big questions surrounding neutron stars. This in turn may help them discover the “tipping point” at which gravity deforms space-time sufficiently to creates a black hole.