Back in 2019, astronomers managing the Laser Interferometer Gravitational-Wave Observatory (LIGO) array of sensors noticed what seemed to be the crash between two ultra-dense neutron stars, for the second time in history.
However, the stars’ mass did not appear to fit humans’ current understanding of astrophysics. The extremely high-powered clash between two neutron stars could determine researchers reanalyze everything they think they know about the Universe, Dr. Enrico Ramirez-Ruiz, an astronomy and astrophysics professor at the University of California at Santa Cruz, said.
The star collision, observed by a LIGO network detector in Livingston, Louisiana, on April 25th, 2019, and named GW190425, was believed to have happened between 290 to 720 million light-years away but had to be powerful enough to send shockwaves that could be identified on Earth, through space-time.
While the first-ever confirmed identification of gravitational waves in 2015 appeared to match astrophysicists’ understanding of neutron stars, these new discoveries do not.
Such Prevalence May be Common
In a study detailing the findings, Ramirez-Ruiz and other colleagues have determined that GW190425’s attributes seem to put scientists’ understanding of the predominance of these types of binary stars in a corner.
First of all, the neutron star couple’s mass, about 3.4 times bigger than that of our Sun, appears to be too big in comparison to that of the about 18 binary neutron star pairs detected in the Milky Way, besides the 2,500 or so identified neutron stars.
Based on LIGO’s observations, it is possible that such massive pairings of stars may be much more normal than researchers previously thought. Perhaps they haven’t been able to identify them because of the lack of omnidirectional sensors such as the ones on LIGO, as well as due to a bias in early radio surveys ‘against observing such systems if they are born from a far-merging channel.’
“Moreover, the comparable merger rate challenges our understanding of supernova explosions in massive stars as more massive new stars are born from heavier progenitors such that the relative formation rate of massive to normal binary neutron star systems should be at least suppressed by an order of magnitude,” the paper reads.
Dr. Benn Farr, an assistant professor of physics at the University of Oregon who is one of the members of the team of researchers studying the findings, said that there is still a lot that researchers do not know about the way binary stars behave.
“We know a great deal about stellar formation and evolution, but a lot of the physics related to producing compact binaries,” he said, “is still very poorly understood.”
Ramirez-Ruiz believes that the difference between the current hypothesis, which stated that less than one in ten neutron stars in the Universe are sufficiently massive to generate gigantic neutron star couples like GW190425, and the recently-discovered opposite is ‘a call to action.
“We have a population of pulsar stars that we see, and all of the binary population models are aimed to explain that population. All of the sudden LIGO says, well, that population is not representative of the population of double neutron stars. So we have to rethink the paradigm of assembly and how these things are made,” he emphasized.