Astronomy Now | 2016 Sep 04
Best known for an enormous eruption in the 1840s that created the billowing,
hourglass-shaped Homunculus Nebula imaged here by
the NASA/ESA Hubble Space Telescope, Eta Carinae is the
most massive and luminous star system within 10,000 light-years.
Image credit: Nathan Smith/UA and NASA.
hourglass-shaped Homunculus Nebula imaged here by
the NASA/ESA Hubble Space Telescope, Eta Carinae is the
most massive and luminous star system within 10,000 light-years.
Image credit: Nathan Smith/UA and NASA.
AnnIn the mid-1800s, astronomers surveying the night sky in the Southern Hemisphere noticed something strange: over the course of a few years, a previously inconspicuous star named Eta Carinae grew brighter and brighter, eventually outshining all other stars except Sirius, before fading again over the next decade, becoming too dim to be seen with the naked eye...
By carefully analysing images of Eta Carinae taken with NASA’s Hubble Space Telescope, Kiminki and her team were surprised to discover that the Great Eruption was only the latest in a series of massive outbursts launched by the star system since the 13th century...
The expansion rate of gas that was far outside the Homunculus indicated that it was moving slowly and must have been ejected centuries before the observed 19th-century brightening. In fact, the motions of the outer material point to two separate eruptions in the mid-13th and mid-16th centuries...
In addition to having a separate origin in time, the older material also showed a very different geometry from the Homunculus, where material was ejected out from the star’s poles and appears symmetric about its rotation axis.
“We found one of the prior eruptions was similarly symmetric, but at a totally different angle from the axis of the Great Eruption,” Kiminki explains. “Even more surprising was that the oldest eruption was very one-sided, suggesting two stars were involved, because it would be very unlikely for one star to blow material out toward just one side.”...
Eta Carinae’s eruptions provide unique insights into the last unstable phases of a very massive star’s life. Researchers who study supernovae have identified a subclass of supernova explosions that appear to suffer violent eruptions shortly before they finally explode. Smith notes that Eta Carinae might be our nearest example of this.
Because it takes light 7,000 years to travel from Eta Carinae to Earth, much could have happened in the meantime, Kiminki says. “Eta Carinae may have gone supernova by now, and we wouldn’t know until 7,000 years from now.”
