The latest update to LIGO’s catalog has doubled the number of confirmed gravitational waves – waves in spacetime caused by catastrophic events. And now, astronomers come to the dire decision of selecting an updated dataset.
In a Nature paper published today, researchers have confirmed the first evidence of two unstable supernovae, doing so with gravitational waves. These unique supernovae occur when massive, extremely hot stars explode in a thermonuclear explosion that destroys the star, leaving nothing behind for anything else that might exist nearby, let alone black holes. Scientists have long assumed that black holes cannot form within this “gap of instability,” which is predicted to range from 50 to 130 times the mass of the Sun. But finding solid evidence of this explosion has proven difficult—until now.
“Unstable supernovas have been difficult to confirm with direct light-based observations because they are rare, distant, and leave small, uniquely detectable remnants,” Hui Tong, lead author of the study and a PhD student at Monash University in Australia, told Gizmodo.
Gravitational waves, on the other hand, allow the tracking of stellar explosions “indirectly”, Tong added, meaning that researchers now have a way to “recreate the effects of stellar explosions indirectly, with the mass of black holes they leave behind.”
Chasing the unseen
Since its Nobel-winning discovery of gravitational waves in 2015, the LIGO Collaboration continues to find surprising signals. Last summer, it announced the discovery of the largest merger ever found, the end product was a black hole more than 225 times the mass of the Sun.
Despite its massive size, the monster black hole’s parents appeared to be lying in an unstable vacuum, 103 and 137 times that of the sun, respectively. The discovery has shown astronomers the potential of gravitational waves to study “invisible” phenomena such as black holes, as well as the need to reexamine our understanding of black hole astronomy.
Tong explained: “Detecting gravitational waves allows us to ‘hear’ the violent collisions of the smallest objects in the universe. That has “opened up a whole new world about the universe,” he added, “revealing previously inaccessible black holes and changing our understanding of how massive stars live and die.”
(The video below is not directly related to the new findings, but it does show what Tong says about the gravitational waves that allow us to “hear” the violent collisions in the universe.)
Analyzing space time
To be clear, the current study deals with the possibility of two supernovas that are completely unstable. Last year’s publication referred to a black hole of two supermassive black holes in a gap thought to have been created by unstable supernovae. So these two results are slightly different in opinion but are intrinsically related in our quest to understand the many unknowns of stellar evolution.
For the new study, Tong and colleagues conducted a statistical analysis of the “cosmic census” of black holes based on LIGO data. According to Tong, their main goal was to “test whether there is a lack of black holes in merging systems at certain masses, as predicted by the physics of the binary instability, and what this can tell us about how black holes and their parent stars form and evolve.”
Their research produced an “unclear” gap in the distribution of the second mass — the smaller of two black holes together — between 44 and 116 times the mass of the Sun, according to the paper. Interestingly, this view allowed the team to follow an indirect path from remnants (black holes) to dying stars (supernovas).
Stay tuned (live)
Tong told Gizmodo that the new findings still require further analysis for astronomers to understand the structure and physical processes of the gap. For Tong, the most surprising aspect of the research is how quickly things are progressing in gravitational wave astronomy. Before 2015, “we had no direct way to know if black holes with masses tens of times the mass of the Sun existed at all because these systems are invisible in light,” he said.
But now, LIGO and its partners are taking hundreds of gravitational pulls – almost every day, at that – giving researchers endless data to test hypotheses like never before. When the next generation of magnetic wave detectors fires up in the 2030s, we could be looking at tens of thousands of signals a year.
Tong said: “This will be a big step forward. “With this richer view, we will be able to compare different views on how massive stars live and die, and connect the observed number of black holes directly to the physics of star formation and nuclear changes.
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