Distant Hot DOG galaxy is a cannibal, ALMA finds

Distant Hot DOG galaxy is a cannibal, ALMA finds

Read time: 3 minutes

Many people eat chicken, cow or pig. Cruel enough, if you think about it. But eating other people is much worse, of course. Eating your own kind is called cannibalism. Luckily, cannibals are very rare.

Now, ALMA has found a cannibal in space: a distant galaxy that is devouring other galaxies. And it’s a very gluttonous cannibal, too: it is feasting on three small galaxies at the same time.

The cosmic greedy-guts was first discovered in 2015. The galaxy is not extremely big, but it is very, very luminous. It emits as much energy as 350 trillion stars like our own sun. In fact, it is the most luminous galaxy that astronomers know of.

All this energy is produced in the galaxy’s core. Right at the center sits a supermassive black hole, 4 billion times more massive than the sun. A disc of superheated gas whirls around the black hole. Nearby clouds of dust are heated up by the radiation from the hot disc. As a result, the dust begins to emit huge amounts of infrared light. Infrared light is heat radiation. Our eyes can’t see it, but special telescopes and satellites can.

Because of all the dust, the core of the galaxy can’t be seen with optical telescopes. That’s why astronomers call it a Hot DOG: a hot, dust-obscured galaxy.

It was already known that the galaxy has three smaller companion galaxies. ALMA has now detected streamers of cool gas that flow from the three companion galaxies into the central Hot DOG galaxy. Apparently, the small galaxies are gobbled up by the larger one, in an act of galactic cannibalism. The streamers contain a very large amount of gas, weighing almost as much as the three small galaxies themselves.

Because the Hot DOG galaxy is so far away, its light took 12.4 billion years to reach Earth. Thus, it is seen as it appeared 12.4 billion years ago, when the universe was still very young. In the future, the galaxy will remain very luminous for at least hundreds of millions of years. That’s because it is eating all this additional gas. Part of the gas will feed the central black hole, so it will remain active for a long time to come. Another part of the gas will turn into new stars.

Never before did astronomers witness cosmic cannibalism at such an early stage in the life of the universe. The ALMA observations provide a unique view of the eating habits of some of the earliest and most extreme galaxies.


The cannibalistic Hot DOG galaxy is officially known as W2246-0526. It was discovered in 2015 by NASA’s Wide-field Infrared Survey Explorer (WISE) – a satellite observatory that detects infrared light from stars and galaxies. The galaxy is located in the constellation Aquarius (the Water Bearer). It is so far away that its light takes 12.4 billion years to reach Earth. Because of the extremely luminous core, it is in fact a so-called quasar. But most quasars are very bright at visible wavelengths, too, while W2246-0526 mainly emits radiation at infrared wavelengths.


The cannibalistic galaxy was studied by Tanio Diaz-Santos of the Universidad Diego Portales in Santiago de Chile. Tanio worked together with astronomers from Chile, the United States, France, the United Kingdom, China and South Korea. The team used ALMA to detect large streamers of cool gas that flow from three companion galaxies to the central Hot DOG galaxy. The results of the ALMA observations have been published in the scientific journal Science.