NASA observatories take an unprecedented look into superstar Eta Carinae

NASA observatories take an unprecedented look into superstar Eta Carinae
Eta Carinae's great eruption in the 1840s created the billowing Homunculus Nebula, imaged here by Hubble. Now about a light-year long, the expanding cloud contains enough material to make at least 10 copies of our sun. Astronomers cannot yet explain what caused this eruption. Credit: NASA, ESA, and the Hubble SM4 ERO Team

Eta Carinae, the most luminous and massive stellar system within 10,000 light-years of Earth, is known for its surprising behavior, erupting twice in the 19th century for reasons scientists still don't understand. A long-term study led by astronomers at NASA's Goddard Space Flight Center in Greenbelt, Maryland, used NASA satellites, ground-based telescopes and theoretical modeling to produce the most comprehensive picture of Eta Carinae to date. New findings include Hubble Space Telescope images that show decade-old shells of ionized gas racing away from the largest star at a million miles an hour, and new 3-D models that reveal never-before-seen features of the stars' interactions.

"We are coming to understand the present state and complex environment of this remarkable object, but we have a long way to go to explain Eta Carinae's past eruptions or to predict its future behavior," said Goddard astrophysicist Ted Gull, who coordinates a research group that has monitored the star for more than a decade.

Located about 7,500 light-years away in the southern constellation of Carina, Eta Carinae comprises two massive whose eccentric orbits bring them unusually close every 5.5 years. Both produce powerful gaseous outflows called , which enshroud the stars and stymy efforts to directly measure their properties. Astronomers have established that the brighter, cooler primary star has about 90 times the mass of the sun and outshines it by 5 million times. While the properties of its smaller, hotter companion are more contested, Gull and his colleagues think the star has about 30 solar masses and emits a million times the sun's light.

Speaking at a press conference at the American Astronomical Society meeting in Seattle on Wednesday, the Goddard researchers discussed recent observations of Eta Carinae and how they fit with the group's current understanding of the system.

At closest approach, or periastron, the stars are 140 million miles (225 million kilometers) apart, or about the average distance between Mars and the sun. Astronomers observe dramatic changes in the system during the months before and after periastron. These include X-ray flares, followed by a sudden decline and eventual recovery of X-ray emission; the disappearance and re-emergence of structures near the stars detected at specific wavelengths of visible light; and even a play of light and shadow as the smaller star swings around the primary.

Explore Eta Carinae from the inside-out with the help of supercomputer simulations and data from NASA satellites and ground-based observatories. Credit: NASA's Goddard Space Flight Center

During the past 11 years, spanning three periastron passages, the Goddard group has developed a model based on routine observations of the stars using ground-based telescopes and multiple NASA satellites. "We used past observations to construct a computer simulation, which helped us predict what we would see during the next cycle, and then we feed new observations back into the model to further refine it," said Thomas Madura, a NASA Postdoctoral Program Fellow at Goddard and a theorist on the Eta Carinae team.

According to this model, the interaction of the two stellar winds accounts for many of the periodic changes observed in the system. The winds from each star have markedly different properties: thick and slow for the primary, lean and fast for the hotter companion. The primary's wind blows at nearly 1 million mph and is especially dense, carrying away the equivalent mass of our sun every thousand years. By contrast, the companion's wind carries off about 100 times less material than the primary's, but it races outward as much as six times faster.

Madura's simulations, which were performed on the Pleiades supercomputer at NASA's Ames Research Center in Moffett Field, California, reveal the complexity of the wind interaction. When the companion star rapidly swings around the primary, its faster wind carves out a spiral cavity in the dense outflow of the larger star. To better visualize this interaction, Madura converted the computer simulations to 3-D digital models and made solid versions using a consumer-grade 3-D printer. This process revealed lengthy spine-like protrusions in the gas flow along the edges of the cavity, features that hadn't been noticed before.

NASA observatories take an unprecedented look into superstar Eta Carinae
In this supercomputer simulation, the stars of Eta Carinae are shown as black dots. Lighter colors indicate greater densities in the stellar winds produced by each star. At closest approach, the fast wind of the smaller star carves a tunnel in the thicker wind of the larger star. Credit: NASA's Goddard Space Flight Center/T. Madura

"We think these structures are real and that they form as a result of instabilities in the flow in the months around closest approach," Madura said. "I wanted to make 3-D prints of the simulations to better visualize them, which turned out to be far more successful than I ever imagined." A paper detailing this research has been submitted to the journal Monthly Notices of the Royal Astronomical Society.

The team detailed a few key observations that expose some of the system's inner workings. For the past three periastron passages, ground-based telescopes in Brazil, Chile, Australia and New Zealand have monitored a single wavelength of blue light emitted by helium atoms that have lost a single electron. According to the model, the helium emission tracks conditions in the primary star's wind. The Space Telescope Imaging Spectrograph (STIS) aboard Hubble captures a different wavelength of blue light emitted by iron atoms that have lost two electrons, which uniquely reveals where gas from the primary star is set aglow by the intense ultraviolet light of its companion. Lastly, X-rays from the system carry information directly from the wind collision zone, where the opposing winds create shock waves that heat the gas to hundreds of millions of degrees.

"Changes in the X-rays are a direct probe of the collision zone and reflect changes in how these stars lose mass," said Michael Corcoran, an astrophysicist with the Universities Space Research Association headquartered in Columbia, Maryland. He and his colleagues compared periastron emission measured over the past 20 years by NASA's Rossi X-ray Timing Explorer, which ceased operation in 2012, and the X-ray Telescope aboard NASA's Swift satellite. In July 2014, as the stars rushed toward each other, Swift observed a series of flares culminating in the brightest X-ray emission yet seen from Eta Carinae. This implies a change in mass loss by one of the stars, but X-rays alone cannot determine which one.

Goddard's Mairan Teodoro led the ground-based campaign tracking the helium emission. "The 2014 emission is nearly identical to what we saw at the previous periastron in 2009, which suggests the primary wind has been constant and that the companion's wind is responsible for the X-ray flares," he explained.

After NASA astronauts repaired the Hubble Space Telescope's STIS instrument in 2009, Gull and his collaborators requested to use it to observe Eta Carinae. By separating the stars' light into a rainbow-like spectrum, STIS reveals the chemical make-up of their environment. But the spectrum also showed wispy structures near the stars that suggested the instrument could be used to map a region close to the binary system in never-before-seen detail.

STIS views its targets through a single narrow slit to limit contamination from other sources. Since December 2010, Gull's team has regularly mapped a region centered on the binary by capturing spectra at 41 different locations, an effort similar to building up a panoramic picture from a series of snapshots. The view spans about 430 billion miles (670 billion km), or about 4,600 times the average Earth-sun distance.

NASA observatories take an unprecedented look into superstar Eta Carinae
Seen in blue light emitted by doubly ionized iron atoms (4,659 angstroms), these images of Eta Carinae were captured by Hubble's STIS instrument between 2010 and 2014. Gas shells created during the binary's 2003 close approach race outward at about 1 million mph (1.6 million km/h). Credit: NASA's Goddard Space Flight Center/T. Gull et al.

The resulting images, revealed for the first time on Wednesday, show that the doubly ionized iron emission comes from a complex gaseous structure nearly a tenth of a light-year across, which Gull likens to Maryland blue crab. By stepping through the STIS images, vast shells of gas representing the crab's "claws" can be seen racing away from the stars with measured speeds of about 1 million mph (1.6 million km/h). With each close approach, a spiral cavity forms in the larger star's wind and then expands outward along with it, creating the moving shells.

"These gas shells persist over thousands of times the distance between Earth and the sun," Gull explained. "Backtracking them, we find the shells began moving away from the primary star about 11 years or three periastron passages ago, providing us with an additional way to glimpse what occurred in the recent past."

When the stars approach, the companion becomes immersed in the thickest part of the primary's wind, which absorbs its UV light and prevents the radiation from reaching the distant gas shells. Without this energy to excite it, the doubly ionized iron stops emitting light and the crab structure disappears at this wavelength. Once the companion swings around the primary and clears the densest wind, its UV light escapes, re-energizes iron atoms in the shells, and the crab returns.

Both of the of Eta Carinae may one day end their lives in supernova explosions. For stars, mass is destiny, and what will determine their ultimate fate is how much matter they can lose—through stellar winds or as-yet-inexplicable eruptions—before they run out of fuel and collapse under their own weight.

For now, the researchers say, there is no evidence to suggest an imminent demise of either star. They are exploring the rich dataset from the 2014 periastron passage to make new predictions, which will be tested when the stars again race together in February 2020.

NASA is exploring our solar system and beyond to understand the universe and our place in it. We seek to unravel the secrets of our universe, its origins and evolution, and search for life among the stars.


Explore further

Eta Carinae: Our Neighboring Superstars

Citation: NASA observatories take an unprecedented look into superstar Eta Carinae (2015, January 7) retrieved 22 July 2019 from https://phys.org/news/2015-01-nasa-observatories-unprecedented-superstar-eta.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
1776 shares

Feedback to editors

User comments

Jan 07, 2015
So how did these stars get so big in the first place through the merger mania scenario? Did they just quietly accrete material until suddenly they became satiated and started constantly burping at a million mph? Certainly the burping would disrupt the accreting? And we just happen to observe the star at this precise moment in it's declining mass history?

Big stars generate new matter therein at an ever-increasing rate, leading to instability and outflows. See Fermi Bubbles and active galactic nuclei.

Jan 07, 2015
Eta Carinae, the most luminous and massive stellar system within 10,000 light-years of Earth, is known for its surprising behavior, erupting twice in the 19th century for reasons scientists still don't understand.


And they will never understand it by using outdated gas dynamics developed in the 19th century in trying to describe these plasma processes. Maybe one day they will arrive in the 21st century.


Jan 07, 2015
So how did these stars get so big in the first place through the merger mania scenario?
Probably not, mergers of stars are very rare and these two likely formed independently from the same gas cloud.
Did they just quietly accrete material until suddenly they became satiated and started constantly burping at a million mph? Certainly the burping would disrupt the accreting? And we just happen to observe the star at this precise moment in it's declining mass history?
Satiated? They accreted the material available to them until they ignited. Same as all stars. Once ignited, they began to emit wind.
Big stars generate new matter therein at an ever-increasing rate, leading to instability and outflows. See Fermi Bubbles and active galactic nuclei.
They don't generate new matter, they fuse one type into another. And, these are stars, not galaxies. Different processes.

Jan 08, 2015
This comment has been removed by a moderator.

Jan 08, 2015
This comment has been removed by a moderator.

Jan 08, 2015
Looking at the first image I always think how scary it would be to be close by (on a ship or even in the next nearest solar system) and see a wall like this racing towards you at several million kilometers per hour.

Jan 08, 2015
I wonder if changes in the orbital period could be measured with sufficient resolution to determine whether the stars are indeed loosing mass, or rather gaining mass. And would such an unexpected deviation be attributed instead to other factors, if the observation did not fit the presumption?

Jan 08, 2015
What a fascinating article on the Eta Carinae system! Up until now, I was unaware that it was a binary system. Makes sense now due to the shape of the nebula, but the amount of extrapolated information thanks to observations is simply amazing!

Jan 08, 2015
by using outdated gas dynamics
and you've already been shown the truth with regard to this continually posted blatant lie, cd
You've made this claim for a year now, and every time you do, you are proven to be a liar with regard to astrophysicists not knowing or learning plasma physics or applying them when applicable... case in point: http://science.na...agercme/
or even here: http://arxiv.org/...92v1.pdf
shall i link the thread where you floundered and proved you couldn't/didn't read as well... i am not so sure it was didn't as much as couldn't anyway

so why do you continue to post this BS?
you would think you would have learned something by now... in fact, you should have learned that repeating a lie doesn't make it any more true than the first time you say it

so ...
quit spreading pseudoscience lies

Jan 09, 2015
Makes sense now due to the shape of the nebula, but the amount of extrapolated information thanks to observations is simply amazing!


Except that we see hundreds of PN's with the double lobed structure that do not contain a binary system. The lobes are not a result of this.



Well, I guess it depends on what you mean. These particular lobes are the result of a binary, and it is pretty clear from the studies that this lobe is shaped by the two stars. Other lobes have different mechanisms to be sure, but that doesn't mean this one isn't exactly what they say it is.

Jan 09, 2015
If this nebulae was shaped by the process modelled, they would have directly stated it, the process modelled wasn't to see if it would produce this structure, that is why they don't claim that it does. The model was designed to reproduce observations from deep inside the nebulae and understand the periodic fluctuations of high energy emmissions.


They didn't explicitly state it because is it a given. If I write about the movement of the Cascadia subduction zone, I don't explicitly state that plate tectonics are involved. The emissions you discuss are the result of the outflow which created the lobe.

Jan 09, 2015
@ reset - I think we are talking past each other a little bit here. The material being emitted by these two stars is being shaped into a lobe structure both by the winds of the two stars and their orbits. This lobe structure is tiny as compared to the nebulae it is embedded in, and is related specifically to the stars themselves. The nebulae, on the other hand, is gigantic.

Take a look at this paper: http://www.etacar...ulus.pdf

Are you suggesting that the stars are not responsible for the material making up the lobes?
Are you suggesting the lobes are not shaped by the stars that produced the material that they are made of?

I am not sure what point you are trying to make here.

Jan 09, 2015
@reset - Well, ok, but there is a huge difference between a PN and the Carinae nebulae. The Carinae nebulae is being lit up by the giant stars that formed in it, and they are relatively young. A PN, on the other hand usually results when a dying star expels its atmosphere after the red giant stage. Eta Carinae is neither of those, although I suppose it is comparable to a PN in that it is the debris cast off by those giant stars. AT 30 and 90 SM, both stars are likely to end in spectacular fashion within a period of something less than a million years.

I think Viper was discussing this actual picture, not the Carinae nebulae in its entirety, although I will leave it to him to clarify if he wants. These stars are a part of that nebulae, but can be properly said to be a nebulae in their own right.

Jan 10, 2015
@reset - Well, ok, but there is a huge difference between a PN and the Carinae nebulae. The Carinae nebulae is being lit up by the giant stars that formed in it, and they are relatively young. A PN, on the other hand usually results when a dying star expels its atmosphere after the red giant stage. Eta Carinae is neither of those, although I suppose it is comparable to a PN in that it is the debris cast off by those giant stars. AT 30 and 90 SM, both stars are likely to end in spectacular fashion within a period of something less than a million years.

I think Viper was discussing this actual picture, not the Carinae nebulae in its entirety, although I will leave it to him to clarify if he wants. These stars are a part of that nebulae, but can be properly said to be a nebulae in their own right.

Your claims are nothing but hypotheses, don't present them as facts.

Jan 10, 2015
cd says
Your claims are nothing but hypotheses, don't present them as facts
i think this proves, more than any other post, that you are illiterate and you read into ANY post exactly what you want to see!

MAG said
I think Viper was discussing
which states that it is conjecture, and concludes with
although I will leave it to him to clarify if he wants
so what part of that was not clear to you?
did this part throw you off?
I suppose it is comparable
or was it simply that you are mad when your pseudoscience is pointed out so that you will attack anyone who is mainstream (or that can support their conjecture with actual evidence)?

have you found a way to prove your own blatant lies about astrophysicists yet?

After all, i gave studies and evidence proving you wrong (yet again) but you've never been able to show where you've been correct yet

your buddies & socks even downvoted it because you were proven wrong
See above

where is that evidence?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more