Location of Eta twins in galaxies M51, M101, NGC 6946, and M83. Individual Image Credits: M51: NASA/ESA/Hubble Heritage Team (STScI/AURA); M101:NASA/ESA/K. Kuntz (JHU), F. Bresolin (U. Hawaii), J. Trauger (Jet Propulsion Lab), J. Mould (NOAO), Y.-H. Chu (U. Illinois, Urbana), Canada-France-Hawaii Telescope/ J.-C. Cuillandre/Coelum/, Jacoby, B. Bohannan, and M. Hanna/ NOAO/AURA/NSF; NGC 6946: NASA/ESA/STScI/R. Gendler/Subaru Telescope (NAOJ); M83: NASA/ESA/Hubble Heritage Team (STScI/AURA) Credit: NASA, ESA and R. Khan (GSFC and ORAU)
Eta Carinae, the most luminous and massive stellar system within 10,000 light-yrs, is best known for an enormous eruption seen in the mid-19th century that hurled an amount of material at least 10X the sun’s mass into space. This expanding veil of gas and dust, which still shrouds Eta Carinae, makes it the only object of its kind known in our galaxy. Now a study using archival data from NASA’s Spitzer and Hubble has found 5 similar objects in other galaxies for the first time.
“The most massive stars are always rare, but they have tremendous impact on the chemical and physical evolution of their host galaxy,” said Rubab Khan, Goddard. These stars produce and distribute large amounts of the chemical elements vital to life and eventually explode as supernovae.
Located ~7,500 light-years away in southern constellation of Carina, Eta Carinae outshines our sun by 5 million times. The binary system consists of 2 massive stars in a tight 5.5-year orbit. The more massive star has about 90X the sun’s mass, while the smaller companion may exceed 30 solar masses.
To understand why the eruption occurred and how it relates to the evolution of massive stars, they needed more examples. Khan et al developed an optical and infrared fingerprint for identifying possible Eta Carinae twins, aka Eta twins. Dust forms in gas ejected by a massive star. This dust dims the star’s UV and visible light, but it absorbs and reradiates this energy as heat at longer, mid-infrared wavelengths. “With Spitzer we see a steady increase in brightness starting at around 3 microns and peaking between 8 and 24 microns,” explained Khan. “By comparing this emission to the dimming we see in Hubble’s optical images, we could determine how much dust was present and compare it to the amount we see around Eta Carinae.”
The team found 2 candidate Eta twins in galaxy M83, 15 million light-years away, and 1 each in NGC 6946, M101, andM51, 18 – 26 million light-years away. These 5 objects mimic the optical and infrared properties of Eta Carinae, indicating that each very likely contains a high-mass star buried in 5 to 10 solar masses of gas and dust.
James Webb Space Telescope (JWST), set to launch in late 2018, carries an instrument ideally suited for further study of these stars. The Mid-Infrared Instrument (MIRI) has 10 times the angular resolution of instruments aboard Spitzer and is most sensitive at the wavelengths where Eta twins shine brightest. “Combined with JWST’s larger primary mirror, MIRI will enable astronomers to better study these rare stellar laboratories and to find additional sources in this fascinating phase of stellar evolution,” said Sonneborn, NASA’s project scientist for JWST operations. It will take JWST observations to confirm the Eta twins as true relatives of Eta Carinae. http://hubblesite.org/newscenter/archive/releases/2016/01/full/
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