This year is rich in discoveries of unusual space objects. So we wrote recently that astronomers have discovered a planet that should not exist. Now, with the help of the Green Bank Telescope, scientists have found the most massive neutron star in the entire observation history. Neutron stars are quite strange – they are almost entirely neutrons and have an incredible density. The mass of the discovered star, which did not receive the most beautiful name J0740 + 6620, is 2.17 times the mass of the sun and its diameter is 30 kilometers. The study is published in the journal Nature Astronomy.
What are neutron stars?
Agree, the universe is a strange thing. It has galactic filaments, galaxy superclusters, dark matter, Fermi bubbles, black holes, neutron stars … the list goes on and on. And if we have recently told you something about the cosmic web, today we propose to pay attention to neutron stars.
First, the denser objects in the universe are only black holes next to the neutron stars. Researchers rightly believe that studying neutron stars can help them understand the extreme physics of the universe – after all, it is these stars that collapse into space monsters. In fact, a neutron star is a massive atomic nucleus that has very strange properties. J0740 + 6620 is thus the densest and strangest neutron star in the entire observation history.
As stars like you and me age and die, their final state depends on the mass. To understand how star stars emerge from dying stars, you must first understand how white dwarfs arise. The fact is that 97% of the stars in the universe are white dwarfs. They consist of electron-nuclear plasma and do not contain any thermonuclear energy sources. In addition, they are the densest compressed star types due to a kind of "built-in" cosmic stop sign after neutrons. Put simply, white dwarfs are so dense that the atomic bonds of their material are broken. As a result, they become a plasma of atomic nuclei and electrons. At the same time, it is quite difficult to achieve a higher density than white dwarfs – the electrons do not want to be in the same state with each other and resist compression to a point where this can happen. Physicists call this the degeneration of electrons.
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Stars whose mass does not exceed 10 solar masses tend to become white dwarfs. The mass limit of the White Dwarves is 1.44 solar masses. But a denser star with a mass of 10 to 29 solar masses can become a neutron star. The fact is, at this moment, the star density is so high that it overcomes the degeneration of the electrons: the electrons still do not want to occupy the same state, so they have to bond with protons, thereby forming neutrons and emitting neutrinos. Neutron stars thus consist almost exclusively of neutrons and are retained due to their degeneracy, which resembles the degeneration of electrons in white dwarfs.
At the same time, the co-author of the study, Scott Ransom, notes that neutron stars have a turning point when their internal density becomes so extreme that gravity inhibits the neutrons ability to withstand another collapse. So, if the mass of J074 + 6620 were larger, the star would simply fall into a black hole. Each "most massive" neutron star, which scientists are gradually discovering, brings experts closer to identifying the inflection point, which prevents the collapse of the neutron star.
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How do astronomers search for neutron stars?
There are at least 100 million neutron stars in the Milky Way, but most of them are old, cold stars, so they are very hard to spot. Fortunately, J0740 + 6620 is a pulsar. Remember, pulsars are the kind of fast-rotating neutron stars that emit radio waves and other electromagnetic radiation. When the pulsar rotates, these rays "pulsate" with enviable regularity, which is somewhat reminiscent of the clock. Most neutron stars are hard to identify, but when the radio waves of the pulsar penetrate the earth, it is much easier to detect and examine them.
The Pulsar J0740 + 6620 lives in a binary system next to a white dwarf. As a white dwarf passed in front of a beam of neutron star radio waves, astronomers on our planet were able to detect a slight deceleration of the incident radio waves. This happened because the white dwarf's gravity curved the space around him and the passing radio waves wandered a touch wider than usual. This measurement allowed astronomers to calculate the mass of the white dwarf. And if you know the mass of an object in a binary system, you can easily calculate the mass of another. The researchers found that J0740 + 6620 is the most massive neutron star so far.
The authors of the study hope that their work will help scientists in areas such as high-energy physics, relativistic astrophysics, and so forth. And all because the fusion of these objects in addition to the properties of the neutron stars listed in the article forms the heaviest elements in the universe.