Why are there no Sumo galaxies?
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People come in different sizes and masses, from little babies to children like yourself or adult persons like your parents. Among the biggest and heftiest people are Japanese Sumo wrestlers – they sometimes weigh more than 200 kilograms!
Galaxies also come in different sizes and masses, from puny dwarf galaxies with just a few million stars to big ones like our own Milky Way Galaxy, which contains a few hundred billion stars. But for some reason, there are almost no supermassive ‘Sumo galaxies’ in the Universe. It is as if the formation of galaxies with extremely large numbers of stars is somehow prevented. But how?
New observations with ALMA – carried out when only 16 of the final 66 antennas were in use – have solved this puzzle. ALMA observed the millimetre waves from cold gas in the Sculptor galaxy. Almost every galaxy contains huge amounts of cold gas – it’s the gas from which new generations of stars are born. But in the Sculptor galaxy, the cold gas is being blown away, out into space. The galaxy is losing the building material for new stars.
The Sculptor galaxy is a so-called starburst galaxy. Starburst galaxies are crowded cosmic nurseries: they contain many young stars, and new baby stars are being born all the time. But the shock waves and the energy from these baby stars blow away the remaining cold gas in the galaxy, with velocities up to a million kilometre per hour.
Every year, the Sculptor galaxy is losing at least ten times more gas than all the gas in our own Sun. At that rate, it won’t take more than 60 million years before all the cold gas is gone. That will mean the end for the formation of new stars in the galaxy.
So the Sculptor galaxy will never end up with huge amounts of stars. The same is probably true for many other galaxies: bursts of star formation are blowing away the building material for new stars. So that’s why there are nu ‘Sumo galaxies’ in the Universe.
As its name implies, the Sculptor galaxy is in the southern constellation the Sculptor, at a distance of some 11 million light-years. It’s also known as NGC 253. It is one of the neares starburst galaxies in the Universe.
The observations of the Sculptor galaxy were carried out by Alberto Bolatto of the University of Maryland in the USA. Alberto worked together with other astronomers from Canada, Germany and the USA. The results are published in the 25 July 2013 edition of the weekly magazine Nature.
Credit: Universe Awareness (unawe.org)