SETI [ASTRO] Trouble Brewing In Eta Carinae


Larry Klaes (lklaes@bbn.com)
Thu, 03 Jun 1999 10:59:44 -0400


>X-Authentication-Warning: brickbat12.mindspring.com: majordom set sender to owner-astro using -f >Date: Wed, 2 Jun 1999 20:31:48 GMT >From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> >To: astro@lists.mindspring.com >Subject: [ASTRO] Trouble Brewing In Eta Carinae >Sender: owner-astro@brickbat12.mindspring.com >Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> > >Bill Steigerwald >Goddard Space Flight Center June 2, 1999 >Greenbelt, MD >William.A.Steigerwald.1@gsfc.nasa.gov >Phone: (301-286-5017) > >RELEASE NO: 99-064 > >TROUBLE BREWING IN ETA CARINAE > >Eta Carinae, a massive star famous for violent outbursts, has doubled in >brightness since early 1998 and now shines more brilliantly than it has in >over a century. Astronomers observing the star with the Space Telescope >Imaging Spectrograph (STIS) onboard NASA's Hubble Space Telescope report >that a recently discovered inner, cone-shaped nebula has brightened >considerably as a consequence. If the brightening continues, Eta Carinae may >have begun a massive eruption like the one in the 1840's that created its >stunning dumbbell shaped nebula. > >"Eta Carinae is at its brightest in visible light since 1864," said Dr. >Theodore Gull of NASA's Goddard Space Flight Center, Greenbelt, Md. "An >inner cone-shaped nebula has tripled its brightness since we first >discovered it in March 1998. There is a lot going on inside the larger Eta >Carinae nebula, and we do not understand all of the activity at this point. >Some of the brightness increase may be due to the excitation of gas in the >nebula by light from Eta Carinae. However, we may also be witnessing the >start of another massive eruption." > >The observations will be the subject of a press conference June 2 at 11 a.m. >EDT during the 100th Anniversary meeting of the American Astronomical >Society in Chicago. > >Eta Carinae is about 7,500 light-years from Earth and appears in the >southern sky in the constellation Carina. At about 100 times the mass of >the Sun, Eta Carinae is a rare luminous blue variable star, a class that >includes the brightest and most massive stars in the universe. Luminous >blue variables are prone to violent displays because of their instability -- >they shine so brightly that their gravity can hardly hold them together. > >In the 1840's, Eta Carinae flared brightly and, over a 20 year period, >ejected enough material to create three Suns. The result of this eruption >can be seen today as a spectacular double-lobed nebula of gas and dust, lit >from within by an intemperate star. The STIS researchers recently found a >cone-shaped nebula inside of the larger nebula. > >"Eta Carinae is unquestionably the most mysterious and powerful star that >we can see with the unaided eye," says Professor Kris Davidson of the >University of Minnesota. "We basically understand how all of the naked-eye >visible stars work -- except Eta Carinae. Its new brightness increase >surprised us for a couple of reasons. First, we thought we had good reasons >not to expect a major outburst in the next few decades. Second, when an >eruption does occur, it shouldn't look like the recent behavior -- the >spectrum should change, and its color should get cooler. Both are contrary >to the data," said Davidson. > >The extremely high resolution of the STIS instrument made the discovery >possible. "We could not separate the activity of Eta Carinae from its >surrounding inner nebula without the very high resolution of the STIS >instrument on Hubble. Its one tenth of an arc-second resolution is like >viewing a baseball from across Lake Michigan. STIS showed us the new, >cone shaped inner nebula as well as revealing the brightness increase >before it was obvious to astronomers on the ground," said Gull. > >Astronomers in Chile, South Africa and Australia confirmed the change in >April, but the effect is less dramatic for them because ground-based >telescopes cannot separate the star from the surrounding outer nebula, >which is half a light year across," said Prof. Roberta Humphreys, also of >University of Minnesota. > >Eta Carinae is one of the brightest known luminous blue variables, a >mysterious category of extremely massive, extremely powerful unstable >stars. The explosion that ends the life of such a massive star is even more >violent than a normal supernova explosion. > >"Only one star in a billion is as massive as Eta Carinae. Some theorists >speculate that such an object ends its life as a hypernova, not a supernova >explosion, and may produce a gamma ray burster, which occurs about once >every 100 million years for each galaxy. A gamma ray burster is such an >cataclysmic event that it might even be hazardous at a distance of 7500 >light years," said Davidson. > >The research group is planning more observations of Eta Carinae in the next >two years. "The STIS instrument combines high resolution imaging with the >ability to get velocity information. We plan to use this powerful >combination to build a three dimensional map of the Eta Carinae nebula, >which will help us understand the beat within its fiery heart," said Gull. > >Editor's note: Images to support this story are available on the internet at: > ftp://PAO.GSFC.NASA.GOV/newsmedia/AAS/ECAR > > >



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