Melina's Physics 111 Blog: Eta Carinae

Eta Carinae is a stellar system in the constellation Carina. It is located about 7,500 to 8,000 light years away from Earth (so its parallax angle is about 0.435 to 0.408 micro arc seconds since 1 parsec = 3.262 light years) with a mass equivalent to that of about 100 solar masses. Its luminosity is known to be about a million times brighter than the sun! It is currently one the biggest and brightest stars in our galaxy. Astronomers who have studied its history and its present conditions suspect it to be a major supernova candidate that could erupt any day now.

History

In the 19^th century, its apparent brightness dramatically increased for two decades, then decreased. This period of time was known as the “great eruption.” No one is absolutely sure on the cause of this eruption. Also parts of the cloud of dust and gas in the two big globes that surround it today are believed to have been released during this dramatic increase in brightness. In 1843 it flared up and became the second brightest star in the sky, after Sirius. It remained this way for about 20 years and then faded, leaving a cloud of gas called the Homunculus Nebula. Eta Carinae has lost about 10% of its substance during that event. Astronomers have called this a “supernova impostor.” After this it returned to be quiet, for an unstable object that is.

From 1976 to 1998, astronomers observed start the South African Astronomical Observatory. During this period of time, they saw an increase across the J, H, K, and L bands, which are filters that allow certain infrared light to pass. However, the reason for this increase in infrared light was unknown at the time.

More Recently

After 1988, the brightness increased more rapidly than a linear trend in the J and H bands. Although this would typically lead observers to believe it is getting hotter, it’s highly unlikely that this is the cause of rapid brightness increase. One theory is that the cloud of dust absorbs blue light, so it is safe to say that this increase could just be the star’s actual brightness, seeing as how the dust could merely be getting destroyed. However this expansion of the cloud that surrounds Eta Carinae is not enough to account for the brightening. Instead it is possibly losing its mass or rotating at a different speed.

In 2005, astronomers discovered that Eta Carinae has at least one companion star. The more massive star, Eta Carinae A, is a blue star. The increase in temperature was most likely due to an overall increase in temperature of some component of the Eta Carinae system, which includes the cloud of dust and gas that surround the massive star.

Although this star has been studied so much by several types of telescopes, there is no theory that has explained what happened.

These changes have lead scientists to believe that the star is becoming more unstable and may be headed towards another eruptive phase, perhaps a second “great eruption.”

Fate

If Eta Carinae does indeed blow up into a supernova, would we be affected? Luckily for us, since we are about 7500 light years away, the radiation from the supernova would not be able to reach us.

These along with many others, are reason astronomers believe Eta Carinae to be a candidate for the next supernova to occur within our galaxy. Especially since there was a star in another galaxy that also seemed like a “supernova impostor” but then a few year later, boom

This star is heading towards instability and eruption and when it goes off it will create a blast so violent that its flash will briefly outshine the entire Milky Way.