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Astronomers using the NSF's Green Bank telescope have identified a record neutron star with the highest mass ever known. The object, called MSP J0740 + 6620, is a fast-spinning millisecond pulsar that packs 2.14 solar masses in a sphere of only 15 km (24 km). This measurement approaches the limits of the mass and compactness of a single object without becoming crushed by a black hole.
MSP J0740 + 6620. Image credit: B. Saxton / NRAO / AUI / NSF.
"Neutron stars are as mysterious as they are fascinating. These objects are essentially huge atomic nuclei. They are so massive that their interiors occupy strange properties, "said Thankful Cromartie, a graduate student at the University of Virginia, and Grote Reber, a researcher at the National Observatory of Radio Astronomy.
"Finding the maximum mass allowed by physics and nature can teach us a lot about this otherwise unreachable area of ​​astrophysics."
"These stars are very exotic. We do not know what they are made of and a very important question is: how can you create one of these stars? This has implications for very exotic material that we simply can not create in a laboratory on Earth, "said Professor Maura McLaughlin of West Virginia University.
Pulsars bear their name because of the double beam of radio waves that they emit from their magnetic poles. These beams sweep the space like a lighthouse.
Some rotate hundreds of times every second. Pulsars rotating with phenomenal speed and regularity, astronomers can use them as the cosmic equivalent of atomic clocks.
This accurate timestamp helps astronomers study the nature of space-time, measure the masses of stellar objects and better understand general relativity.
In the case of the MSP J0740 + 6620, located some 4600 light-years away from the Earth and approaching the surface of our planet, this cosmic precision allowed astronomers to calculate the mass of the two stars.
When the ticking pulsar passes behind its white dwarf companion, there is a subtle delay in the time of arrival of the signals – a phenomenon known as Shapiro Delay.
In essence, the gravity of the white dwarf star slightly distorts the space around it, according to Einstein's theory of general relativity. This warping means that the pulses of the rotating neutron star must move a little further while they bypass the space-time distortions caused by the white dwarf.
Astronomers can use the amount of this delay to calculate the mass of the white dwarf. Once the mass of one of the co-orbiting bodies is known, the precise determination of the mass of the other is a relatively simple process.
"The focus of this binary star system has created a fantastic cosmic laboratory," said Dr. Scott Ransom, astronomer at the National Observatory of Radio Astronomy.
"Neutron stars have this tipping point where their inner densities become so extreme that the force of gravity exceeds even the neutrons' ability to resist a new collapse. Each "most massive" neutron star we find brings us closer to identifying this tipping point and helps us understand the physics of matter at these breathtaking densities. "
The research was published in the journal Nature Astronomy.
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H.T. Cromartie et al. Relatively relativistic, Shapiro delays the measurement of an extremely massive pulsar, millisecond. Nature Astronomy, published online September 16, 2019; doi: 10.1038 / s41550-019-0880-2
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