The closest pair of black holes to Earth, in a new image from the Very Large Telescope

The protagonist of this image is the galaxy Ngc 7727, 89 million light years away in the constellation Aquarius, the result of the collision of two smaller galaxies.

A collision between two galaxies is not like that between two cars: the stars that form them practically never collide, because the space between them is too large and the stars are too small for it to be a statistically relevant phenomenon. 

Typically the collision between two galaxies is much more like a dance, in which each of the two revolves around its partner under the influence of reciprocal gravity;  large tails of material, stars, gas and dust are formed, like the beautiful ones visible in this image;  finally the two galaxies merge into a single large galaxy.  Using the instruments of the Very Large Telescope of the European Southern Observatory, the researchers then studied this galaxy in depth, analyzing its properties and structure to reconstruct its past evolution and envision its future.

The collision between the two galaxies would have begun about a billion years ago, but it is not yet complete: in the center, the two nuclei of the galaxies that formed it persist, separated.  They are two supermassive black holes, one of 153 and the other of 6 million solar masses, separated by only 1600 light years from each other: they are very close to each other and will melt within the next 250 million years.  At that point a single gigantic black hole will arise, and Ngc 7727 will have a single core.

Anne Mare

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