"Attention, astronomers! Please keep a close eye on Eta Carinae! It's acting up again."
OK, that's not exactly how Dan Green worded the announcement in IAU Circular 9094 on November 11th, but the gist of his alert was crystal clear. On August 19th Kris Davidson and Andrea Mehner (University of Minnesota), along with John Martin (University of Illinois at Springfield) and others, used the Hubble's Space Telescope Imaging Spectrograph (STIS) to show that one of the most massive and unstable stars known has surged in brightness over the past six months. Now at magnitude 5.1, it's fairly easy picking with the unaided eye for southern-sky observers. And there's every indication that more surprises are in the offing.
STIS, by the way, is now back in action after failing in 2004 — and that's especially welcome in this case, since it's too bright to be imaged by Hubble's new Wide-Field Camera 3 (as Martin notes in a comment below).
When we last left this rogue star's ongoing saga, researchers were debating whether an 1843 outburst that made Eta Carinae the night sky's second-brightest star resulted from a violent internal explosion or the radiation-driven escape of matter off its surface. And with the realization that Eta Carinae is actually a binary star, there's no way to tell which half is causing trouble — or what will happen next.
With 90 to 100 times the Sun's mass and some 5,000,000 times its luminosity, Eta Carinae's two stars close to within 1 or 2 astronomical units of each other every 5½ years &mdash most recently last January.
Now there's evidence that X-rays created as outflowing winds from these heavyweight suns crash together have strengthened and gained energy, "a possible indicator that the star is entering a new unstable phase of mass loss," according to Michael Corcoran (USRA).
This remarkable rogue star is probably in the last gasps of its brief but spectacular life. By some estimates Eta Carinae might take a few thousand years to blow itself to smithereens. But its mimicry of other luminous blue variables that have abruptly become supernovae — such as SN 2006jc, which flared in 2004 and went kapow two years later) has raised speculation that the end might come within our lifetimes or even in a few years!
(Don't worry — it's at least 7,000 light-years away.)
So the deathwatch continues. Astronomers have mounted observing campaigns with the Hubble Space Telescope and at La Plata Observatory in Argentina. Observers also plan to compare notes next January during a meeting of the American Astronomical Society.