Black holes are often perceived as cosmic ogres, destroyers of stars. And yet, observations carried out thanks to the high resolution of the Hubble Space Telescope show that sometimes they can also give birth to stars in galaxies.
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Expected during the 1930s by Subramanyan Chandrasekhar and especially Robert Oppenheimer, the black holes relativists (Laplace and Mitchell already conceived them in physical Newtonian) were not taken seriously for decades and it was not until the 1960s, with the discovery of quasars, that visionary pioneers like John Wheeler, Roger Penrose or of course stephen hawking gave their letters of nobility to these objects exotic.
Soon enough, black holes became world-destroyers to the general public and science fiction fans, swallowing stars or spaceships. From astrophysicists, like Jean Pierre Luminet and Brandon Carter, will also develop scenarios in the early 1980s, with supporting calculations, showing how a star passing too close to one of the supermassive black holes that we were beginning to discover in large numbers in the heart of the great galaxies could be distorted by tidal forces, to the point of taking a pancake shape and then exploding. It is the phenomenon of Tidal disruption event (or TDE), which can be translated as “tidal rupture event”.
We are therefore a little surprised by the announcement made by two astrophysicists via an article published in Nature and which concerns a irregular galaxy named Henize 2-10.
Black holes, destroyers and creators of stars. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose “French”. © NASA’s Goddard Space Flight Center
Streams of matter collapsing molecular clouds
Henize 2-10 (its name is a tribute to Karl G. Henize, a astronomer American who was astronaut of the Nasa on board of skylab and sadly deceased on Everest) is a dwarf galaxy located approximately 34 millionlight years of the Milky Way in the constellation of the Compass. Its diameter is only about 3,000 light-years but it nevertheless contains a supermassive black hole of about a million masses solar. This is already in itself surprising because our Galaxy, thirty times larger, contains a supermassive black hole of about 4.3 million solar masses.
But what is most surprising is that the observations made with Hubble clearly seem to show that winds of matter from the central black hole of Henize 2-10 not only are associated with open clusters young people stars on their way, but that the stream of matter they constitute connects like a umbilical cord this black hole and a region, the seat of a feverish formation of stars about 230 light-years from the compact star.
Analysis of the information provided by Hubble indicates that the flow of matter was emitted from the black hole a few million years ago and that the shock waves with clouds molecules on the passage of this flow caused their collapse and therefore the formation of young stars.
Of course, powerful jets of matter from supermassive black holes have long been observed, but they are usually too hot and too energetic inside galaxies. Instead of causing the clouds in their path to collapse, they heat and expand them, making it impossible for stars to form.
A quasar could build its galaxy!
Article of Laurent Sacco published on 03/12/2009
It has long been suspected that galaxies and supermassive black holes grow together. New observations from quasar HE0450-2958 show that a giant black hole can cause part of the galaxy to form that will house it in its core. This scenario could be very common in the Universe.
After the nature of Kerr black hole rotating giant has been recognized as the engine responsible for the tremendous energy of quasars and active galactic nuclei, astrophysicists had discovered a strange relationship. The size of the central black hole is proportional to the size of its galaxy. A good way to account for this observation is to assume a co-genic link between supermassive black holes and galaxies.
It was not clear, however, who was at the origin of the other. A black hole needs matter to grow and one can imagine that of a forming galaxy accumulating in the center, eventually creating a black hole. Conversely, its gravitational force can attract a lot of matter around it and we can also imagine a cloud of gas spinning around a vast black hole and eventually forming a galaxy. In short, the problem is one of chicken and egg. However, some clues showed that so-called intermediate-mass black holes may predate the first galaxies and may have more or less served as germ for the growth of these primordial galaxies.
We also know that large galaxies are formed by merger dwarf galaxies. Their black holes being destined to merge after a certain time, in all probability, there was a way to explain, at least in part, the relationship between the mass of a galactic black hole and the mass of a galaxy.
We also know that when a giant black hole ignites into a quasar, it emits a stream of particles and radiation that can influence and regulate the rate of star formation in a galaxy.
However, we have known for some time about the quasar HE0450-2958, located some 5 billion light-years from Earth. It didn’t really seem to be located in a galaxy even if matter falling on the black hole was bound to be present in significant quantities. Astrophysicists had immediately proposed that due to a large quantity of dust interposed between the host galaxy of HE0450-2958 and us, this matter was invisible.
A cloud of gas jostled by a jet of matter
If this hypothesis were correct, observations in infrared should reveal it. astronomers David Elbaz and Knud Jahnke have therefore, literally, tried to see things more clearly with their colleagues by means of an instrument of the Very Large Telescope (the VLT) of the ESO, capable of observing in the mid-infrared range.
As Knud Jahnke, member of the Emmy Noether-Group on Coevolution of Galaxies and Black Holes of the MPIA : “ by observing these wavelengths we could have detected the dust supposedly hiding the host galaxy. However, we did not find any. Instead, we discovered that a seemingly unrelated galaxy in the immediate vicinity of the quasar was producing stars at a breakneck rate. “.
The rate of formation of new stars is indeed very high there, about 350 suns per year, a hundred times more than in the typical galaxies of the local Universe. Moreover, a remarkable fact too, as in the case of the quasar 3C 321, the galaxy located just 22,000 light-years from HE0450-2958 is hit hard by one of the quasar’s jets of matter.
By injecting energy into a large cloud of gas, this jet of matter could have caused at least the appearance of a new galaxy and certainly that of new stars. However, as David Elbaz points out, these two objects will inevitably merge in the future: the quasar moves at a speed only a few tens of thousands of kilometers per hour relative to the galaxy. Although the quasar is still “naked”, it will eventually be “clothed” when it merges with its star-rich galaxy. It will eventually reside inside a galaxy like all other quasars “.
This is enough to specify models linking the growth of galaxies and the growth of supermassive black holes. Jets of matter from quasars could play an important role. But this almost unique case cannot suffice. We would have to probe the Universe more deeply to show that this example, without necessarily being the rule, was very widespread in the Universe during its first billion years of existence. This should be one of the tasks of the next generation of giant telescopes, as Alma (Atacama Large Millimeter/submillimeter Array), L’E-ELT (the European Giant Telescope) or Hubble’s successor, the James Web Space Telescope.
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