Stars have two "lives"

Rebirth observed in Sakurai's Object

"Rebirth" of an old star Institute for Astrophysics / Leopold Franzens University Innsbruck
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An international team of astrophysicists has witnessed an extraordinary cosmic event: an old star, which had already arrived at the end of its normal life, is unexpectedly quickly shining in new splendor.

In rare cases, such a star "ignites" again, instead of becoming stellar slag. Previously, it was suspected that this process takes several hundred years. This time, however, a flare could be observed after only a few years. This forces the researchers, led by Professor Albert Zijlstra of the University of Manchester, to reconsider their ideas about the reawakening of stars.

The astrophysicists with the participation of the Innsbruck researcher Professor Stefan Kimeswenger studied the star V4334 Sgr in the constellation of Sagittarius. Known in professional circles as "Sakurai's Object". The star showed a strong increase in brightness in 1996. At first, astrophysicists believed that this outbreak was a common nova explosion. Subsequent research showed that "Sakurai's Object" was not a nova.

The models were confirmed with the Radio Interferometer of the National Radio Observatory in New Mexico, the Hubble Telescope and the "Very Large Telescope" of the European Southern Observatory in Chile. The researchers report on their findings in the current issue of Science Journal Science.

Re-igniting fusion reactions possible

Computer simulations had predicted how such a reignition of fusion reactions would follow. The observed star did not follow these models. In reality, the event was 100 times faster than predicted in the simulations. "We have now developed a new theoretical model. The new observations have provided the first evidence supporting our model, "said Kimeswenger. display

The star is an old white dwarf who no longer had hydrogen for nuclear fusion reactions in its interior. Astrophysicists believe that such stars sometimes shine brightly in a final flare of nuclear fusion. However, the eruption of "Sakurai's Object" is the first to be observed in recent times.

Flare 100 times faster than expected

The original calculation models predict a period of a few hundred years for the flare-up. This assumption proved incorrect. "Sakurai's Object" went through the first stages of this process in a few years - 100 times faster than we expected. That's how we had to review and adapt our models, "says Kimeswenger.

The new models predict that the star will heat up again very quickly, reaching its maximum in temperature and brightness in a few years. In this state, he will linger a bit and then slowly cool again. "Finally, there will be another heating episode before the star turns into stellar slag in a final cooling, " predicted Kimeswenger.

(University of Innsbruck, 08.04.2005 - DLO)