The Major Star

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Giant lobes of gas billow out from monster stars at the heart of Eta Carinae, the biggest star system in our part of the universe.

The gas clouds, which extend ten trillion kilometres into space, are known as the Homunculus Nebula. They were created by a massive explosion between 1837 and 1856, which turned Eta Carinae into one of the brightest objects in the sky.

Located some 7500 light-years away in the southern constellation of Carina, the highly luminous expanding double bubbles of ionised gas and dust ejecta move outwards at about a million kilometres per hour, and contain enough material to make at least 10 Suns.

These lobes are actually 100,000 times fainter than the brilliant central stars.

Separating the two lobes is a faint disk called the equatorial skirt, which astronomers say appears to contain slightly younger material than the lobes.

Like Russian babushka dolls, the Homunculus Nebula is just the outermost layer of a series of smaller and smaller shells known as the Little Homunculus, and Baby Homunculus.

At the heart of the nebula are two monstrous blue stars producing powerful stellar winds of ionised gas.

The primary star is thought to be between 90 and 120 times the mass of the Sun.

The star’s stellar winds blow at some 1.6 million kilometres per hour, and are especially dense, carrying away the equivalent mass of our Sun every thousand years. These winds are so powerful, they prevent astronomers from actually seeing the star.

Astronomers predict this star will explode as a supernova or hypernova in the astronomically near future.

The smaller, secondary star is about 30 times as massive as the Sun. Its stellar winds carry about 100 times less material than the primary star, but are hotter and six times faster.

When the stellar winds from both stars collide, they reach temperatures of hundreds of millions of degrees, generating a flood of X-rays.

Every five and a half years the two stars come within 225 million kilometres of each other — about the same distance that Mars is from the Sun.

In the months before and after the stars reach their closest point, Eta Carinae undergoes dramatic changes, producing massive X-ray flares, followed by a sudden decline and eventual recovery of X-ray emissions as the smaller star ploughs through and carves out a spiral cavity inside the stellar winds of its larger companion.

This image, taken by the Hubble Space Telescope, is made up of a sequence of eight exposures in red and near-ultraviolet filters, which were subsequently combined to produce the final colour picture.

Dulce María Sáez Martínez

Jesús Sánchez García

Pablo Dorador Ontiveros

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