Wonders of the Universe

A STAR IS BORN

Our sun is in the middle of its life cycle, but look out into the Milky Way and we can see the whole cycle of stellar life playing out. Roughly once a year a new light appears in our galaxy, as somewhere in the Milky Way a new star is born.

The Lagoon Nebula is one such star nursery; within this giant interstellar cloud of gas and dust, new stars are created. Discovered by French astronomer Guillaume Le Gentil in 1747, this is one of a handful of active star-forming regions in our galaxy that are visible with the naked eye. This huge cloud is slowly collapsing under its own gravity, but slightly denser regions gradually accrete more and more matter, and over time these clumps grow massive enough to turn into stars.

The centre of this vast stellar nursery, known as the Hourglass, is illuminated by an intriguing object known as Herschel 36. This star is thought to be a ‘ZAMS’ star (zero ago main sequence) because it has just begun to produce the dominant part of its energy from hydrogen fusion in its core. Recent measurements suggest that Herschel 36 may actually be three large young stars orbiting around each other, with the entire system having a combined mass of over fifty times that of our sun. This makes Herschel 36 a true system of giants. Eventually Herschel 36 and all the stars in the Milky Way will die, and when they do, many will go out in a blaze of glory.

Eta Carinae is a pair of billowing gas and dust clouds that are the remnants of a stellar explosion from an unstable star system. The system consists of at least two giant stars, and shines with a brightness four million times that of our sun. One of these stars is thought to be a Wolf-Rayet star. These stars are immense, over twenty times the mass of our sun, and are engaged in a constant struggle to hang onto their outer layers, losing vast amounts of mass every second in a powerful solar wind. In 1843, Eta Carinae became one of the brightest stars in the Universe when it exploded. The blast spat matter out at nearly 2.5 million kilometres (1.5 million miles) an hour, and was so bright that it was thought to be a supernova explosion. Eta Carinae survived intact and remains buried deep inside these clouds, but its days are numbered. Because of its immense mass, the Wolf-Rayet star is using up its hydrogen fuel at a ferocious rate. Within a few hundred thousand years, it is expected that the star will explode in a supernova or even a hypernova (the biggest explosion in the known Universe), although its fate may be sealed a lot sooner. In 2004, an explosion thought to be similar to the 1843 Eta Carinae event was seen in a galaxy over seventy million light years from the Milky Way. Just two years later, the star exploded as a supernova. Eta Carinae is very much closer – at a distance of only 7,500 light years – so as a supernova it may shine so brightly that it will be visible from Earth even in daylight.

Out in the Milky Way we can see the whole cycle of stellar life playing out. Roughly once a year a new light appears, as somewhere in the Milky Way a new star is born.

Eta Carinae is one of the most massive and visible stars in the night sky, but because of its mass it is also the most volatile and most likely to explode in the near future.

NASA

Seeing the light from these distant worlds and watching the life cycle of the Universe unfold is a breathtaking reminder that light is the ultimate messenger; carrying information about the wonders of the Universe to us across interstellar and intergalactic distances. But light does much more than just allow us to see these distant worlds; it allows us to journey back through time, providing a direct and real connection with our past. This seemingly impossible state of affairs is made possible not only because of the information carried by the light, but by the properties of light itself

Eventually all the stars in the Milky Way will die, many in spectacular explosions. Herschel 36 was formed from just such a stellar explosion, which occurred within the Eta Carinae system.