Astronomers unveil 'heart' of Eta Carinae

November 16, 2016

An international team of astronomers has imaged the Eta Carinae star system in the greatest detail ever. Eta Carinae is a colossal binary system that consists of two massive stars orbiting each other. It is found almost 8,000 light years from Earth within the Carina Nebula, a giant star-forming region in the Carina-Sagittarius Arm of the Milky Way.

The images enabled the astronomers to observe unexpected new structures in the binary system, including a region between the two stars in which extremely high-velocity stellar winds are colliding.

"With these observations, we were able to map the zone in which the two stellar winds collide and make sure we genuinely understand the basic parameters of the binary system," said Augusto Damineli, Full Professor at the University of São Paulo's Institute of Astronomy, Geophysics & Atmospheric Sciences (IAG-USP) in Brazil.

Damineli has studied mysterious phenomena involving Eta Carinae for more than 20 years with FAPESP's support and is one of the three Brazilian authors of the paper published by Astronomy & Astrophysics.

The other two are Mairan Macedo Teodoro, a researcher at NASA's Goddard Space Flight Center, and José Henrique Groh de Castro Moura, a professor at Trinity College Dublin in Ireland.

According to the researchers, the Eta Carinae binary pair are so massive and bright that the radiation they produce rips atoms off their surfaces and spews them into space. This expulsion of atomic material is referred to as stellar wind.

The raging winds from Eta Carinae are much faster and denser than the solar wind streaming off our own Sun. They collide violently in the zone between the two stars at speeds that can reach 10 million km per hour.

The combined effect of the two stellar winds as they smash into each other at extreme speeds is to create temperatures of millions of degrees and intense deluges of X-ray radiation.

The central area where the raging winds collide is so comparatively tiny that telescopes in space and on the ground have not been able to image them in detail - until now.

Utilizing an advanced new imaging technique called infrared long baseline interferometry, which combines light beams collected from the same astronomic object by several telescopes to analyze it in great detail, the researchers were able to observe the turbulent collision zone for the first time.

They did this with the Astronomical Multi-Beam Recombiner known as AMBER, an instrument currently installed on the Very Large Telescope Interferometer (VLTI) at the European Southern Observatory's Paranal Facility in Chile's Atacama Desert.

They used three of the VLT's four auxiliary telescopes, each with a diameter of 1.8 m and mounted on tracks so that they can move up to 200 m apart.

Image sharpness increases with telescope separation, so the astronomers were able to achieve a tenfold increase in resolving power compared with one of the VLT array's main telescopes, delivering for the first time direct images 50,000 times finer than human vision of both the wind that swirls around Eta Carinae's primary star and the wind collision zone between the two stars.

Using the Doppler effect, which enables astronomers to calculate precisely how fast stars and other astronomical objects are moving toward or away from Earth, they obtained images of the stellar winds at different velocities, measuring velocities and densities to compare them with a computer model of the collision.

"The images we obtained via the Doppler effect show the stellar winds colliding at different velocities," Damineli said. "So we were able to use them to reconstruct the shape of the walls of the cavity formed by the collision shockwave from its apex to the most distant regions."

The researchers also observed in the images an unexpected fan-shaped structure where the raging wind from the smaller, hotter star crashes into the denser wind from the larger of the pair.

The wind from the secondary star is less dense but much fiercer than the wind from the primary star, reaching velocities of 3,000 km per second, they estimated.

On the basis of these stellar wind velocities, they hope to be able to create more accurate computer models of Eta Carinae's internal structure and increase their understanding of how extremely massive stars lose mass as they evolve.

"Because light from the secondary star is 200-300 times weaker than light from the primary, we couldn't see it directly with AMBER," Damineli said. "We should be able to do so with GRAVITY, a new VLTI instrument due to come on stream soon."

GRAVITY is an interferometric instrument operating in the K band and combining four telescope beams. Its higher resolution will enable the astronomers to obtain interferometric images of astronomic objects with even greater precision and over a wider range of wavelengths.

According to Damineli, they may succeed in tracking Eta Carinae's secondary star from point to point along its 5.5-year orbit and plotting its ellipse.

"When we've done that we'll at last be able to 'weigh' the secondary star. Mass is a star's most fundamental parameter," he said.

Fundação de Amparo à Pesquisa do Estado de São Paulo

Related Astronomers Articles from Brightsurf:

Astronomers are bulging with data
For the first time, over 250 million stars in our galaxy's bulge have been surveyed in near-ultraviolet, optical, and near-infrared light, opening the door for astronomers to reexamine key questions about the Milky Way's formation and history.

Astronomers capture a pulsar 'powering up'
A Monash-University-led collaboration has, for the first time, observed the full, 12-day process of material spiralling into a distant neutron star, triggering an X-ray outburst thousands of times brighter than our Sun.

Astronomers discover new class of cosmic explosions
Analysis of two cosmic explosions indicates to astronomers that the pair, along with a puzzling blast from 2018, constitute a new type of event, with similarities to some supernovae and gamma-ray bursts, but also with significant differences.

Astronomers discover planet that never was
What was thought to be an exoplanet in a nearby star system likely never existed in the first place, according to University of Arizona astronomers.

Canadian astronomers determine Earth's fingerprint
Two McGill University astronomers have assembled a 'fingerprint' for Earth, which could be used to identify a planet beyond our Solar System capable of supporting life.

Astronomers help wage war on cancer
Techniques developed by astronomers could help in the fight against breast and skin cancer.

Astronomers make history in a split second
In a world first, an Australian-led international team of astronomers has determined the precise location of a powerful one-off burst of cosmic radio waves.

Astronomers witness galaxy megamerger
Using the Atacama Large Millimeter/submillimeter Array (ALMA), an international team of scientists has uncovered a startlingly dense concentration of 14 galaxies that are poised to merge, forming the core of what will eventually become a colossal galaxy cluster.

Astronomers discover a star that would not die
An international team of astronomers has made a bizarre discovery; a star that refuses to stop shining.

Astronomers spun up by galaxy-shape finding
For the first time astronomers have measured how a galaxy's spin affects its shape -- something scientists have tried to do for 90 years -- using a sample of 845 galaxies.

Read More: Astronomers News and Astronomers Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to