Scientists from the Observatories Network Ligo-Virgo-Karga they detected the “gravitational echo” of fusion of more colossal black holes ever recorded. This record event, called GW231123has been observed indirectly through gravitational waves-ripples in the fabric of space-time-produced by the collision of a black hole of 140 solar masses and one 100 solar masseswhose fusion produced a single black hole of 225 solar masses. The previous record dates back to a similar event detected in 2021 which produced a black hole of 140 solar masses.
The signal dates back to November 23, 2023, but the announcement only arrives now because it has served more than a year and a half of analysis to reach a sufficient degree of security on the interpretation of the collected data. The discovery is particularly interesting because it represents one interpretative challenge for physicists and astrophysicians: such high mass black holes cannot be produced directly from the death of massive stars, therefore it is supposed that they have been generated through previous mergers. In addition, at least one of the two protagonists of this violent cosmic collision showed signs of such a rapid rotation that it is precisely to the limit of what allows Einstein’s relativity.
The scientific explanation of the record fusion: what physics says
First of all, let’s clarify that a black hole is not an astrophysical object like the others. It is not a “ball” made of some material, as can be a star or planet, but one region of space-time: in particular, a region of space-time characterized by a gravity so intense as to prevent the transmission towards the outside of any type of information from the subject contained within it.
Black holes are formed when a mass is compressed beyond a certain volume limit: this creates an imaginary “border” in space-time, called horizon of eventswhich hides the content of the black hole itself to the rest of the universe. To give you an idea, if we wanted to transform the entire planet Earth into a black hole we should compress it until it reaches the size of an Arachide! In fact, the only known mechanism capable of doing something like that is catastrophic implosion of the nucleus of very massive stars (at least 20 solar masses) which takes place when some supernovae explodes.
At this point, a black hole can grow if something ends inside or merging with another black hole, as happened in this case. And here the most attentive of you will have noticed an important detail: if the two black holes were 140 and 100 solar masses, because the resulting black hole is not 240 solar masses? Where is the missing mass over?
The answer is that it has turned into energy. When we are dealing with highly energetic events, such as nuclear fusion or the merger of black holes or neutron stars, this fact is far from unusual. The possibility of converting mass into energy or vice versa is established by the most famous formula of all physics, AND = MC2that we have to great Albert Einstein. The formula says that from a mass m It can be converted into an amount of energy AND which is the same as the starting mass for the square of the speed of light c (about 300 million meters per second).
In this case the beauty of 15 solar massesthat is, the difference between the 240 expected and the 225 actual. We are talking about something like 30,000 billion billions of billions of kg which, using Einstein’s formula, give us a frightening value 2.7 · 1048 joule! It is an energy thousands of billions of billions of billions of times higher than that freed from the most powerful nuclear device ever made, the Zar bomb.
How to observe a fusion of black holes: gravitational waves
Like a free explosion of shock waves in the air, the merger of two very high gravity objects such as black holes produces “shock waves” in the very fabric of space-time: it is waves of gravity who are named gravitational waves. The space-time deformation effect at a great distance is however incredibly smallless than the size of an atomic nucleus. This is why incredibly precise tools are needed, called interferometersto detect gravitational waves. It is no coincidence that it is something we started doing only ten years ago, in 2015!
Analyzing every detail of the gravitational waves detected, scientists are able to reconstruct them “backwards” the cause that produced them: in this case, the properties of the two black holes and the dynamics of their merger.
The GW231123 event was recorded by the network of detectors Ligo-Virgo-Karga. Ligo (Gravitational-Wave Observatory laser interferometer laser) consists of two twin detectors in the United States: it was the observatory that in 2015 detected the first gravitational waves never observed. Virgo Instead it is an Italian interfermetre, located near Pisa, while Kagra (Kamioka Gravitational Wave Detector) is located in Japan. Together, these three consortia recorded over 300 blacks of black holes.
Because this discovery is important
As we said, it is the first time that such a “massive” fusion is observed between black holes, however too high mass to be the direct result of a supernova explosion. Events like this can therefore help us understand the complex astrophysical mechanisms on “Genealogy of black holes”that is, as “small” black holes of stellar origin evolve over time into increasingly large black holes, to form the Supermassicci black holes that occupy the center of almost all galaxies. At the moment very little is known about the growth of black holes: that’s why these observations are very precious for astrophysics.
The dizzying rotation of the two black holes is also very interesting. “They seem to rotate very quickly, close to the limit allowed by Einstein’s theory of general relativity,” he explained Charlie Hoymember of the LVK network. «This makes the signal difficult to model and interpret. It is an excellent case of study to push the development of our theoretical tools ».
