Astronomers First Discovered A Pair Of Neutron Stars With Very Different Masses
Astronomers have discovered an exotic pair of neutron stars with very different masses in the constellation of the eagle. They can be used to measure the rate of expansion of the Universe. The article with the results of the research is available in the scientific journal Nature.
"Most of the theories are based on the assumption that merging neutron stars have the same mass. Our discovery calls this into question," said one of the authors of the work, an astrophysicist from the University of East Anglia (UK), Robert Ferdman.
Neutron stars are the remnants of large burned-out stars. After a supernova explosion, their cores "collapse" into a small sphere that is comparable in size to a small city. The matter inside them is compressed so much that the result is a chain of reactions in which electrons and protons merge. After that, the entire former star turns into a ball of neutrons.
Due to their large mass and small size, neutron stars will interact very strongly with any neighbors that are very close to them in terms of gravity. Rotating around each other, both objects will lose energy, generating gravitational waves, and gradually come closer. Because of this, pairs of neutron stars and their combinations with other types of luminaries are very interesting for astrophysicists who study the nature of gravity.
For the first time, as noted by Ferdman and his colleagues, scientists were able to track a similar event in August 2017, when the LIGO and VIRGO gravitational observatories recorded gravitational waves from the merger of two neutron stars in the galaxy NGC 4993 for the first time in history. This process was accompanied by a flash of light, which was observed by about a third of all astronomers on Earth.
The first observations of the event GW170817, as scientists began to call it, unexpectedly indicated that the collision of neutron stars did not go according to the scenario predicted by theoretical models. In particular, due to their merging, an excessively large amount of matter was released and a relatively weak flash of almost all types of electromagnetic waves.
Weighing a star
This discrepancy, according to scientists, can be explained by the fact that the mass of one of the neutron stars was about 20% lower than that of the other. As a result, just before merging with the second neutron star, the first one collapsed. However, the theory held that this could not be. This has generated a lot of theoretical debate about the nature of GW170817.
By observing the pulsar PSR J1913+1102, Ferdman and his colleagues obtained the first evidence that the masses of neutron stars in close pairs of similar luminaries can really differ greatly. This pulsar is located in the constellation of the eagle at a distance of 23 thousand light-years from Earth and is a double neutron star with a combined mass of about 2.88 times that of the sun.
By measuring how much the signals from each neutron star" lag "or" rush," deviating from the typical frequency of their formation, scientists were able to calculate their mass very accurately.
These measurements showed that the PSR J1913+1102 system contains two neutron stars that are about 1.62 and 1.27 times heavier than the Sun. As scientists suggest, the larger pulsar appeared first, after which it began to capture the matter of the progenitor of a smaller neural star, which spun it and led to the death of the second star.
Now, these objects are located at a relatively large distance from each other, about 1.25 million km. The gravitational waves they produce are too weak to be detected by LIGO or other gravitational wave detectors. For the same reason, scientists assume that in the distant future, in about 470 million years, they will collide.
On the other hand, the discovery of this "non-equilibrium" pair of neutron stars in the immediate vicinity of the Earth suggests that such objects are quite common in space. Their existence explains the anomalous nature of the gw170817 flare, and also gives astronomers hope that subsequent discoveries of such mergers will help them learn how neutron stars work, as well as to measure the rate of expansion of the Universe and conduct new tests of the theory of relativity.