- An international team of scientists, including Australian researchers from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), have collaborated on a study released today, presenting the largest number of gravitational wave detections to date — 90 detections!
- Gravitational waves are cosmic ripples in space and time that are caused by some of the most violent and energetic processes in the Universe, like supernovas, merging black holes, and colliding neutron stars — city-size stellar objects with a mass about 1.4 times that of the Sun.
- The newest gravitational wave detections come from the second part of the third observing run which lasted from November 2019 to March 2020. There were 35 new gravitational wave detections in this period: 32 detections were from pairs of merging black holes; 3 were likely to come from the collision of a
Of these 35 new events, here are some notable discoveries (the numbers in the names are the date and time of the observation):
- Two mergers between possible neutron star — black hole pairs. These are called GW191219_163120 and GW200115_042309, the latter of which was previously reported in its own publication. The neutron star in GW191219_163120 is one of the least massive ever observed.
- A merger between a black hole and an object which could either be a light black hole or a heavy neutron star called GW200210_092254
- A massive pair of black holes orbiting each other, with a combined mass 145 times heavier than the Sun (called GW200220_061928)
- A pair of black holes orbiting each other, in which at least one of the pair is spinning upright (called GW191204_171526)
- A pair of black holes orbiting each other which have a combined mass 112 times heavier than the Sun, which seems to be spinning upside-down (called GW191109_010717)
- A ‘light’ pair of black holes that together weigh only 18 times the mass of the Sun (called GW191129_134029)
The different properties of the detected black holes and neutron stars are important clues as to how massive stars live and then die in supernova explosions.
“It’s fascinating that there is such a wide range of properties within this growing collection of black hole and neutron star pairs,” says study co-author and OzGrav PhD student Isobel Romero-Shaw (Monash University). “Properties like the masses and spins of these pairs can tell us how they’re forming, so seeing such a diverse mix raises interesting questions about where they came from.”
Not only can scientists look at individual properties of these binary pairs, they can also study these cosmic events as a large collection — or population. “By studying these populations of black holes and neutron stars we can start to understand the overall trends and properties of these extreme objects and uncover how these pairs came to be,” says OzGrav PhD student Shanika Galaudage (Monash University) who was a co-author on a companion publication released today: ‘The population of merging compact binaries inferred using public alerts for possible detections are typically released within a few minutes of the observation. Rapid public alerts are an important way of sharing information with the wider astronomy community, so that telescopes and electromagnetic observatories can be used to search for light from merging events — for example, merging neutron stars can produce detectable light.
Says Dr. Aaron Jones, co-author and postdoctoral researcher from The University of Western Australia, “It’s exciting to see 18 of those initial public alerts upgraded to confident gravitational wave events, along with 17 new events.”
After thorough and careful data analysis, scientists then decipher the shortlist of gravitational-wave detections, delving into the properties of the systems that produced these signals. They use parameter estimation, a statistical technique to learn information about the black holes and neutron stars, such as their masses and spins, their location on the sky and their distance from the Earth.
All of these detections were made possible by the global coordinated efforts from the continuous gravitational waves, and of course new surprises!
For more on this research, read Massive “Tsunami” of Gravitational Wave Detections Breaks Record.