The Keyhole Nebula

Keyhole_NebulaThe Keyhole is a small dark cloud of cold molecules and dust within the Carina Nebula, containing bright filaments of hot, fluorescing gas that is silhouetted against the much brighter background nebula. The diameter of the Keyhole structure is roughly 7 light years. Its appearance has changed significantly since it was first observed, possibly due to changes in the radiation from Eta Carinae.

Image Credit: NASA

A Possible Scenario

These six panels show a possible scenario for the powerful blast seen 170 years ago from the star system Eta Carinae.

1. Eta Carinae initially was a triple-star system. Two giant stars (A and B) in the system were orbiting closely and a third companion C was orbitint much farther away.

2. When the more massive of the close binary stars (A) neared the end of its life, it began to expand and lost most of its material, which fell into its slightly smaller companion (B).

3. As the companion (B) grew to about 100 solar masses, it became extremely bright. Meanwhile, the donor star (A) was losing its outer hydrogen layers, exposing its hot helium core. The shift in the masses of the stars altered the gravitational balance of the system, and the helium-core star moves farther away from its monster sibling.

4. As it moved outward, the now smaller, but still quite large, helium-core star interacted gravitationally with the outermost star (C), pulling it into the fray. The two stars traded places, as the outermost star was kicked inward.

5. The massive inner stat’s gravity interacted with Star C, moving inward, creating a disk of material around the giant star.

6. Eventually, star C merged with the inner star, producing an explosive event that formed the bipolar lobes of material ejected. Meanwhile, the surviving companion, A, settles into an elongated orbit around the merged pair. Every 5.5 years it passes through the giant star’s outer gaseous envelope, producing shock waves that are detected in X-rays.

Image Credit: NASA / ESA / SRScI

The Homunculus Nebula

A massive pair of gas and dust clouds have been blown outward from the supermassive star Eta Carinae. A sequence of eight images taken through red and near-ultraviolet filters by the Hubble Space Telescope have been combined to produce this color image. Multiple exposures necessary to cover the nebula’s wide dynamic range: the outer blobs are 100,000 times fainter than the central star. Eta Carinae exploded about 160 years ago and became one of the brightest stars in the southern sky. Even though the star released as much visible light as a supernova explosion, it survived and produced the two lobes and a large, thin equatorial disk, all moving outward at about 1 million km/h.

Image Credit: NASA

A Doomed Star

etacarinae_hst_960Eta Carinae may be about to explode. We’re not sure when—it might be next year, it might be one million years from now. The star’s mass of roughly 100 times our Sun’s makes it an excellent candidate for a full blown supernova, and about 150 years ago, Eta Carinae underwent an unusual outburst becoming one of the brightest stars in the southern sky. Eta Carinae is also the only star currently known to be emitting light from a natural laser. This Hubble image brings out details in the unusual nebula that surrounds this rogue star—two distinct lobes, a hot central region, and strange radial streaks. The lobes are filled with lanes of gas and dust which absorb the blue and ultraviolet light emitted near the center. The streaks remain unexplained.

Eta Carinae is in the constellation Carina. Carina is Latin for the keel of a ship, and it was formerly part of the larger constellation of Argo Navis (the ship Argo) until that constellation was divided into three pieces, the other two being Puppis (the poop deck), and Vela (the sails of the ship).

Image Credit: NASA