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Astronomers working with data from the Chandra X-ray space observatory said this week (25 September 2019) that they had located three supermassive black holes on a collision course. The system in which this merger of three black holes is in progress is called SDSS J0849 + 1114. It is located about a billion light-years away from Earth. Telescopes on the ground and in space, including Chandra, Hubble, WISE and NuSTAR, have captured the scene, which scientists call:
… The best proof to date for a trio of giant black holes.
So we have not seen many systems like this yet. And yet, astronomers believe that triplet collisions like this play a vital role in the growth of the largest black holes over time. Ryan Pfeifle of George Mason University in Fairfax, Virginia, is the first author of a new article in the Astrophysical Journal, which describes these results (preprinting here). He said:
We were only looking for pairs of black holes at the time, and yet, thanks to our selection technique, we came across this incredible system. This is the strongest evidence that has been found for such a triple active power system of supermassive black holes.
The statement of these scientists describes their process:
The researchers had to combine telescope data on the ground and in space to discover this rare black hole. First, the Sloan Digital Sky Survey telescope, which sweeps large swaths of the sky in New Mexico's optical light, took an image of the SDSS J0849 + 1114. With the help of citizen scientists participating in a project called Galaxy Zoo, it was later identified as a collision system of galaxies.
Next, data from NASA's Wide-field Infrared Survey Explorer (WISE) mission revealed that the system was shining intensely in the infrared during a phase of galaxy fusion during which several black holes eat fast. To follow these clues, astronomers then turned to Chandra and the large binocular telescope in Arizona.
Chandra's data revealed X-ray sources – a tell-tale sign of material consumption by black holes – at the light centers of each galaxy of fusion, exactly where scientists expect supermassive black holes resident. Chandra and NASA's network of nuclear spectroscopy telescopes (NuSTAR) have also revealed large amounts of gas and dust around one of the black holes, typical of a system of black holes in fusion.
Co-author Christina Manzano-King of the University of California, Riverside, said:
Optical spectra contain a wealth of information on a galaxy. They are commonly used to identify supermassive black holes that actively accumulate and can reflect the impact they have on the galaxies that they inhabit.
These astronomers have explained that one of the reasons it is difficult to find a triplet of supermassive black holes is that the holes are probably wrapped in gas and dust, blocking much of their light. The infrared images of WISE, the infrared spectra of LBT and the radiological images of Chandra bypass this problem, they said, because infrared and X-ray light penetrate gas clouds much more easily than optical light. Pfeifle explained:
Using these main observatories, we have identified a new way to identify supermassive triple black holes. Each telescope gives us a different clue about what's going on in these systems. We hope to extend our work to find more triples using the same technique.
Shobita Satyapal, also of George Mason, also explained why this system is exciting for scientists:
Double and triple black holes are extremely rare, but such systems are actually a natural consequence of galaxy fusions, which we believe is the mode of growth and evolution of galaxies.
As you might expect, these scientists have stated that the fusion of three supermassive black holes behaves differently than a pair:
When there are three of these interacting black holes, one pair should blend into a larger black hole much faster than if the two were alone. This could be a solution to a theoretical riddle called "parsec's final problem", in which two supermassive black holes can approach a few light-years away from each other, but would require an effort extra to blend because of excess energy. they carry in their orbits. The influence of a third black hole, as in SDSS J0849 + 1114, could finally bring them closer.
Computer simulations have shown that 16% of pairs of supermassive black holes in colliding galaxies will have interacted with a third supermassive black hole before fusion. These fusions will produce ripples in space-time called gravitational waves. These waves will have lower frequencies than those detected by the National Science Foundation's laser interferometer gravitational wave observatory (LIGO) and the European Virgo detector. However, they may be detectable with radio observations of pulsars, as well as future space observatories, such as the European Space Agency's Laser Interferometer Spatial Antenna (LISA), which will detect black holes up to a million solar masses.
In summary: astronomers have discovered a system of 3 galaxies – called SDSS J0849 + 1114 – that have orbited a billion light-years from Earth. Each galaxy contains a supermassive black hole, which overlap, about to collide.
Via Chandra
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