In the late phases of binary neutron star development, the huge star expands and engulfs the neutron star buddy in a stage referred to as common-envelope evolution (a). Less-massive removed stars experience an additional mass transfer stage that even more removes the star and recycles the pulsar buddy, leading to systems such as the observed binary neutron stars in the Milky Way and GW170817 (b). Typically, the only way to see a binary neutron star system, such as the one that developed the GW190425 gravitational wave signal, is if one of the 2 stars in the system is a pulsar and then connects with its routine neutron star neighbor. None of the known binary neutron star systems had heavy sufficient stars to match the signal seen by LIGO.
They did not have such stars partially due to bigger stars turning into black holes rather than neutron stars when they die.
They are more able to hold on to their mass rather than moving it to their binary companion, letting it light up as a pulsar.
A whole population of large neutron star binary systems might exist, undetectable to our normal detection techniques. Now, with LIGO, we must at least be able to see when they merge, and that is another step towards truly comprehending them.
Initially released on Universe Today.
For more on this research, see Astrophysicists Explain Puzzling Results From Gravitational Wave Observatories.
Reference: “Fallback Supernova Assembly of Heavy Binary Neutron Stars and Light Black Hole– Neutron Star Pairs and the Common Stellar Ancestry of GW190425 and GW200115” by Alejandro Vigna-Gómez, Sophie L. Schrøder, Enrico Ramirez-Ruiz, David R. Aguilera-Dena, Aldo Batta, Norbert Langer and Reinhold Willcox, 8 October 2021, Astrophysical Journal Letters.DOI: 10.3847/ 2041-8213/ ac2903.
It depends on 2 aspects: the weight of the core thats left and the forcefulness of its supernova surge.
Utilizing stellar evolution models, the group showed that for helium stars, some of the outer layers of helium can be blown off in the explosion, decreasing the weight of the star to the point where it is no longer able to become a black hole. That could possibly explain where the heavy neutron stars come from, however why arent they more noticeable in binary systems with pulsars?
Usually, the only way to see a binary neutron star system, such as the one that produced the GW190425 gravitational wave signal, is if one of the 2 stars in the system is a pulsar and then interacts with its routine neutron star next-door neighbor. None of the recognized binary neutron star systems had heavy enough stars to match the signal seen by LIGO.
When they pass away, they lacked such stars partially due to bigger stars turning into black holes rather than neutron stars. The gravitational signals were coming from merging huge neutron stars, not merging black holes. So what is triggering the development of these big neutron stars, and why arent they appearing in binary pairs with pulsars?
In the late stages of binary neutron star formation, the huge star expands and swallows up the neutron star buddy in a phase referred to as common-envelope evolution (a). Ejection of the envelope leaves the neutron star in a close orbit with a stripped-envelope star. Less-massive stripped stars experience an additional mass transfer stage that even more removes the star and recycles the pulsar buddy, leading to systems such as the observed binary neutron stars in the Milky Way and GW170817 (b).
The verification of gravitational waves back in 2017 continues to open entire new worlds of physics however also continues to elicit further concerns. The detection of each gravitational wave brings a brand-new difficulty– how to discover out what caused the event. Sometimes that is more difficult than it sounds. Now a team led by Alejandro Vigna-Gomez of the University of Copenhagen believes they found a model of star death that assists to explain some previously inexplicable findings– and indicate a galaxy with much more massive neutron stars than formerly thought.
In science, it prevails to collect information that does not appear to fit the present scientific theory. That sort of unanticipated information originated from the Laser Interferometer Gravitational-Wave Observatorys ( LIGO) second-ever gravitational wave finding. Usually, LIGO would tape gravitational waves resulting from the collision of 2 massively thick items, such as a great void and a neutron star. When it comes to its 2nd favorable recording, at first taped in 2019 and now known as GW190425, the data pointed to the source as being two merging neutron stars, but they were remarkably big..
