A team of astronomers has discovered through the Green Bank Telescope (GBT) in Virginia (USA) the most massive neutron star in the universe to date. This pulsar, called J0740 + 6620, is a collapsed core of a colossal star, which had a total mass of 10 to 29 solar masses before it collapsed. The typical mass of the remaining core is about 1.4 solar masses.
Despite their enormous mass, neutron stars are incredibly small when it comes to their physical size . In general, its radius is only about 10 kilometers. Just imagine for a moment that an object with a radius of only 10 kilometers has a mass greater than that of our Sun, we are already beginning to understand how fabulous and intense they are, since neutron stars are potentially the densest type of star. of the universe.
J0740 + 6620 is a rapidly rotating pulsar with 2.17 times the mass of the sun (which is 333,000 times the mass of the Earth) in a sphere of only 20-30 kilometers. This measurement approaches the limits of how massive and compact a single object can become without collapsing a black hole.
The star was detected approximately 4,600 light years distant from Earth.
These findings, from the NANOGrav Physics Frontiers Center, funded by the National Science Foundation, have been published in the journal Nature Astronomy.
The present discovery is one of many fortuitous in nature, said Maura McLaughlin, a co-author of the work, that emerged during routine observations taken as part of a search for gravitational waves.
Mysterious and fascinating
Astronomers measured the mass of this pulsar through a phenomenon known as “Shapiro’s Lag .” Basically, the gravity of the pulsar’s white dwarf companion, a small, dense star that co-orbits in orbit around the neutron star, warps the fabric of space and time around it by a degree proportional to the mass of the dwarf. White. These distortions in space-time delay the pulsar’s pulses by tens of millionths of a second as it passes behind the white dwarf from Earth’s point of view. Scientists can measure these delays to calculate the mass of the white dwarf. By analyzing how the pulsar and the white dwarf orbit each other, they can estimate the mass of the pulsar.
“At Green Bank, we are trying to detect gravitational waves from pulsars. To do that, we need to observe many millisecond pulsars, which are rapidly spinning neutron stars. This is not a gravitational wave detection document, but one of the many important results that have emerged from our observations, “says McLaughlin.
These types of objects have been studied for decades, but there are still many mysteries about their nature. For example, we do not know if they decompose into a soup of subatomic quarks or other exotic particles and when and how gravity defeats matter and forms a black hole …
“These stars are very exotic. We don’t know what they are made of and a really important question is, ‘ How massive can one of these stars get?’ It has implications for very exotic material that we simply cannot create in a laboratory on Earth, “McLaughlin explains.
Analyzing the pulsar measurement
A pulsar is a magnetized rotating neutron star or white dwarf that emits beams of electromagnetic radiation. These rays that pass through space are reminiscent of a lighthouse as it radiates its light in a circle. However, when it comes to how fast they spin, there is a little difference. Pulsars can spin hundreds of times per second. This spin is so regular that scientists can use it as something akin to an atomic clock. Time helps scientists study the mysterious features of space-time, measure the masses of stellar objects, and improve their understanding of general relativity.
Regarding “Shapiro’s time lag”
Shapiro’s time delay effect is a classic proof of general relativity. Basically, the gravity of the white dwarf star slightly warps the space around it, following Einstein’s general theory of relativity. This deformation means that the oscillations from the spinning neutron star have to travel a little further because they have to circumvent the space-time distortions created by the white dwarf. Scientists can use the significance of that delay to determine the mass of the white dwarf.
Scott Ranson, a co-author of the paper, claimed that the orientation of this binary star system created a fantastic cosmic laboratory . Each ‘more massive’ neutron star discovery will bring scientists closer to identifying the tipping point where gravity defeats the ability of neutron stars not to collapse into a black hole.
We live in exciting times when it comes to the field of astrophysics. This latest discovery only adds to our excitement and with the next giant ground-based telescopes and future advanced space telescopes, this is probably only just beginning.
Referencia: Relativistic Shapiro delay measurements of an extremely massive millisecond pulsar, Nature Astronomy (2019). DOI: 10.1038/s41550-019-0880-2 , https://nature.com/articles/s41550-019-0880-2
