\u201cThis is the most massive black hole merger we\u2019ve detected through gravitational waves, and its interpretation provides both a major clue and a major challenge for our understanding of black hole formation processes,\u201d says Dr. Juan Calder\u00f3n Bustillo, Ram\u00f3n y Cajal researcher at IGFAE, a joint center of the University of Santiago de Compostela and the Xunta de Galicia.<\/p>\n
So far, approximately 100 black hole mergers have been observed via gravitational waves. The largest had been the one known as GW190521 \u2014 discovered in 2019 \u2014 with a significantly smaller total mass: \u201conly\u201d 140 times the mass of the Sun, whose analysis was led by Calder\u00f3n Bustillo. \u201cNow we\u2019ve broken our own record, nearly doubling the mass!\u201d he highlights.<\/p>\n
An IGFAE technique to study generations of black holes<\/strong><\/h4>\nIn addition to their enormous mass, these two black holes are spinning rapidly on their own axes. These two aspects make this signal uniquely challenging to interpret and suggest a complex formation history.<\/p>\n
\u201cIn principle, black holes like these shouldn\u2019t be able to form from the collapse of stars at the end of their lives. Therefore, it\u2019s possible that these two black holes resulted from successive previous mergers of smaller black holes,\u201d explains Juan Calder\u00f3n Bustillo. This is where one of IGFAE\u2019s main contributions to the discovery lies: techniques developed by the Institute\u2019s team, which have already been used in recent studies to understand the origin of such events.<\/a><\/p>\n\u201cWith these techniques, we\u2019ve been able to reconstruct the genealogy of these black holes. We found that the larger one is very likely a \u2018third-generation\u2019 black hole \u2014 meaning that, at best, its \u2018grandparents\u2019 would have formed from stellar collapse.\u201d<\/p>\n
![\"\"](\"https:\/\/igfae.usc.es\/igfae\/wp-content\/uploads\/gw231123-scaled.jpg\")
<\/p>\n
Pushing the limits of general relativity and detection systems<\/strong><\/h4>\nThe large mass and rapid spin of the black holes in the GW231123 signal push to the limit both the algorithms used for gravitational wave detection and the theoretical models that allow for their interpretation. Detecting such massive systems requires sophisticated techniques, the development of which IGFAE has led over the past five years.<\/p>\n
\u201cSignals from systems like GW231123 are extremely short and easily confused with artificial signals that continuously contaminate our detectors,\u201d explains Dr. Thomas Dent, Distinguished Researcher at IGFAE since 2018 and founder of its gravitational wave research program.<\/p>\n
\u201cOne of our main lines of work is the development of complex techniques to rule out artificial signals. This allows us to optimize the sensitivity of our detection systems,\u201d says Dent. \u201cIn fact, the PyCBC system we developed here was the one that provided what we call the \u2018quick alert\u2019 that something had been detected.\u201d Ultimately, extracting precise information from the signal required theoretical models that capture the complex dynamics of rapidly spinning black holes.<\/p>\n
In the future, the IGFAE team will continue refining their analyses and improving the models used to interpret these extreme events. \u201cIt will take years to truly understand the nature of these kinds of sources,\u201d predict Juan Calder\u00f3n Bustillo and Thomas Dent.<\/p>\n
\u201cThese types of signals often allow for multiple interpretations. While the most likely one seems to be a merger of two black holes in a circular but \u2018oscillating\u2019 orbit, future studies might reveal that it\u2019s actually an eccentric orbit \u2014 or, as has been proposed before, perhaps we\u2019re seeing something beyond black holes altogether,\u201d they add.<\/p>\n
Thomas Dent concludes, \u201cAlongside the necessary theoretical developments, the accumulation of more observations like this will allow us to investigate much more deeply how such black holes form and how the stars that once died to give them life \u2014 or to give life to their ancestors \u2014 actually behaved.\u201d<\/p>\n
Gravitational waves and IGFAE\u2019s role in LIGO<\/strong><\/h4>\nGravitational waves are ripples in the fabric of space-time that travel at the speed of light, produced by the most violent events in the universe, such as black hole mergers or stellar explosions (supernovae). They were first predicted theoretically by Albert Einstein over 100 years ago, but weren\u2019t directly observed until 2015, when the LIGO collaboration succeeded in doing so.<\/p>\n
This achievement became one of the greatest milestones in physics in recent decades. Three of the main architects of the discovery \u2014 Kip Thorne<\/a>, Barry C. Barish, and Rainer Weiss \u2014 received the Nobel Prize in Physics in 2017, among many other honors.<\/p>\n
\u201cWith these techniques, we\u2019ve been able to reconstruct the genealogy of these black holes. We found that the larger one is very likely a \u2018third-generation\u2019 black hole \u2014 meaning that, at best, its \u2018grandparents\u2019 would have formed from stellar collapse.\u201d<\/p>\n
<\/p>\n
Pushing the limits of general relativity and detection systems<\/strong><\/h4>\nThe large mass and rapid spin of the black holes in the GW231123 signal push to the limit both the algorithms used for gravitational wave detection and the theoretical models that allow for their interpretation. Detecting such massive systems requires sophisticated techniques, the development of which IGFAE has led over the past five years.<\/p>\n
\u201cSignals from systems like GW231123 are extremely short and easily confused with artificial signals that continuously contaminate our detectors,\u201d explains Dr. Thomas Dent, Distinguished Researcher at IGFAE since 2018 and founder of its gravitational wave research program.<\/p>\n
\u201cOne of our main lines of work is the development of complex techniques to rule out artificial signals. This allows us to optimize the sensitivity of our detection systems,\u201d says Dent. \u201cIn fact, the PyCBC system we developed here was the one that provided what we call the \u2018quick alert\u2019 that something had been detected.\u201d Ultimately, extracting precise information from the signal required theoretical models that capture the complex dynamics of rapidly spinning black holes.<\/p>\n
In the future, the IGFAE team will continue refining their analyses and improving the models used to interpret these extreme events. \u201cIt will take years to truly understand the nature of these kinds of sources,\u201d predict Juan Calder\u00f3n Bustillo and Thomas Dent.<\/p>\n
\u201cThese types of signals often allow for multiple interpretations. While the most likely one seems to be a merger of two black holes in a circular but \u2018oscillating\u2019 orbit, future studies might reveal that it\u2019s actually an eccentric orbit \u2014 or, as has been proposed before, perhaps we\u2019re seeing something beyond black holes altogether,\u201d they add.<\/p>\n
Thomas Dent concludes, \u201cAlongside the necessary theoretical developments, the accumulation of more observations like this will allow us to investigate much more deeply how such black holes form and how the stars that once died to give them life \u2014 or to give life to their ancestors \u2014 actually behaved.\u201d<\/p>\n
Gravitational waves and IGFAE\u2019s role in LIGO<\/strong><\/h4>\nGravitational waves are ripples in the fabric of space-time that travel at the speed of light, produced by the most violent events in the universe, such as black hole mergers or stellar explosions (supernovae). They were first predicted theoretically by Albert Einstein over 100 years ago, but weren\u2019t directly observed until 2015, when the LIGO collaboration succeeded in doing so.<\/p>\n
This achievement became one of the greatest milestones in physics in recent decades. Three of the main architects of the discovery \u2014 Kip Thorne<\/a>, Barry C. Barish, and Rainer Weiss \u2014 received the Nobel Prize in Physics in 2017, among many other honors.<\/p>\n
Gravitational waves are ripples in the fabric of space-time that travel at the speed of light, produced by the most violent events in the universe, such as black hole mergers or stellar explosions (supernovae). They were first predicted theoretically by Albert Einstein over 100 years ago, but weren\u2019t directly observed until 2015, when the LIGO collaboration succeeded in doing so.<\/p>\n
This achievement became one of the greatest milestones in physics in recent decades. Three of the main architects of the discovery \u2014 Kip Thorne<\/a>, Barry C. Barish, and Rainer Weiss \u2014 received the Nobel Prize in Physics in 2017, among many other honors.<\/p>\n