From the southern hemisphere you can see, through a modest telescope or binoculars, a faint diffuse point called Centaurus A or NGC 5128. Located 16 million light-years away, its active center produces enormous amounts of high-energy emissions. Seen in detail, a situation is discovered that astronomers consider completely out of place: an elliptical galaxy with a bar of matter crossing its center.
If there is one thing that is clear, it is that elliptical galaxies do not have dust clouds like spirals, much less a bar crossing them from side to side. On the other hand, radio telescopes have found that two jets of matter emerge from the center of this active galaxy. That stick of dust, gas, and stars may be the fuel that powers the engine of these jets. If it happens like in other galaxies, it must be a super black hole .
Now, what happens in Centaurus A? Many astronomers think this is one of the most terrifying phenomena in the universe: an example of galactic cannibalism , where a huge elliptical galaxy has literally swallowed a passing spiral. What we are now observing is how it is digesting several hundred million years…
Meanwhile, in the constellation of Pavo there is a system discovered by the infrared satellite IRAS and that has obtained its name from the catalog of sources detected by the satellite, IRAS 19254-7245. A difficult name to remember, and for this reason he is better known by the nickname of the Super Antenna .
Located 800 million light-years away, it is made up of two galaxies on a collision course: one, small and faint, seen face-on, and another 3 times more massive than ours, seen edge-on. Its nickname is due to the surprising similarity of its appearance with NGC 4038-39, two nearby galaxies that are colliding in the constellation of the Raven and that, due to their peculiar structure, are called Antenna.
The Super Antenna is 5 times larger and 10 times brighter in the infrared. But the real cannibalism seems to be happening 2.3 billion light-years from us, in the Shakhbazian 1 cluster of galaxies. There 24 galaxies, each 30 billion solar masses, are packed into a space just over six times the diameter of the Milky Way, 650,000 light-years. Are we facing a true galactic bacchanal ?
The Milky Way is a swallow
Something similar happens with our galaxy. Beautifully shaped, large and symmetrical, the Milky Way looks like a finished product. However, in recent years we have discovered that our beloved cosmic city may still be unfinished.
The Milky Way continues to scoop up cosmic material by gobbling up small, faint galaxies that venture nearby and risk being sucked into its gravitational well, like flies in honey. In fact, it is thought that when the universe was young, all the galaxies like the Milky Way grew thanks to a slow but continuous collection of smaller ones. Today the process continues , but at a slower pace.
A dramatic example is the small spheroidal galaxy Sagittarius that is merging into the disk of our galaxy, luckily on the other side of where we are. Discovered by accident in 1994, the Sagittarius dwarf has 1% of the mass of the Galaxy and its vision is obscured by the Milky Way itself. Today we know that the gravity of our galaxy is deforming it, stretching it, like a pastry chef with its mass, and a stream of stars is slowly “falling” on us. In fact, astronomers from the Instituto de Astrofisica de Canarias discovered part of the “debris” of Sagittarius, just over 18,000 light-years from the center of the Milky Way.
On the other hand, studying the movement of the stars in the galactic disk, it has been discovered that it is “inflating” due to the fact that a satellite galaxy was absorbed by ours 10 billion years ago. If this were not enough, it is more than likely that the largest and brightest globular cluster in the Milky Way, Omega Centauri , is not what it seems, but is what remains of the heart of a dwarf galaxy that we devoured long ago.
Will this intergalactic billiards ever end? No. At least not for the next 3 million years. By then the Andromeda galaxy, M31, and us will merge in a long and deep cosmic embrace…
