Eta Carinae - X-ray Source

X-ray Source

4U 1037–60 (A 1044–59) is Eta Carinae. Three structures around Eta Carinae are thought to represent shock waves produced by matter rushing away from the superstar at supersonic speeds. The temperature of the shock-heated gas ranges from 60 MK in the central regions to 3 MK on the horseshoe-shaped outer structure. "The Chandra image contains some puzzles for existing ideas of how a star can produce such hot and intense X-rays," says Prof. Kris Davidson of the University of Minnesota.

A "spectroscopic minimum", or "X-ray eclipse", appeared in 2003. Astronomers organized a large observing campaign which included every available ground-based (e.g. CCD optical photometry) and space observatory, including major observations with the Hubble Space Telescope, the Chandra X-ray Observatory, the INTEGRAL Gamma-ray space observatory, and the Very Large Telescope. Primary goals of these observations were to determine if, in fact, Eta Carinae is a binary star and, if so, to identify its companion star; to determine the physical mechanism behind the "spectroscopic minima"; and to understand their relation (if any) to the large-scale eruptions of the 19th century.

There is good agreement between the X-ray light curve and the evolution of a wind-wind collision zone of a binary system. These results were complemented by new tests on radio wavelengths.

Spectrographic monitoring of Eta Carinae showed that some emission lines faded every 5.52 years, and that this period was stable for decades. The star's radio emission, along with its X-ray brightness, also drop precipitously during these "events" as well. These variations, along with ultra-violet variations, suggest a high probability that Eta Carinae is actually a binary star in which a hot, lower-mass star revolves around η Carinae in a 5.52-year, highly eccentric elliptical orbit.

The ionizing radiation emitted by the secondary star in Eta Carinae is the major radiation source of the system. Much of this radiation is absorbed by the primary stellar wind, mainly after it encounters the secondary wind and passes through a shock wave. The amount of absorption depends on the compression factor of the primary wind in the shock wave. The compression factor is limited by the magnetic pressure in the primary wind. The variation of the absorption by the post-shock primary wind with orbital phase changes the ionization structure of the circumbinary gas, and can account for the radio light curve of Eta Carinae. Fast variations near periastron passage are attributed to the onset of the accretion phase.