Jul 2 2019
The Hubble Space Telescope provides an unusual view of the expanding gases of the double star system Eta Carinae, glowing in blue, white, and red colors.
Telescopes, including Hubble, have monitored the Eta Carinae star system for more than two decades. It has been prone to violent outbursts, including an episode in the 1840s during which ejected material formed the bipolar bubbles seen here. (Image credit: NASA, ESA, N. Smith (University of Arizona, Tucson), and J. Morse (BoldlyGo Institute, New York))
To date, this is the highest resolution image of Eta Carinae to be captured by the NASA/ESA Hubble Space Telescope.
Envisage slow-motion fireworks that began to explode about two hundred years ago and have not ceased since then. This is how one might elucidate the double star system—Eta Carinae—situated 7500 light-years away in the constellation Carina, or The Ship’s Keel.
In the year 1838, the double star system went through a catastrophic outburst known as the Great Eruption, rapidly growing to become the second brightest star in the sky by April of 1844.
Since then, the star has faded, but this latest and unique view provided by the NASA/ESA Hubble Space Telescope demonstrates that the remarkable display is still continuing, revealing details that previously were never seen.
In the history of Eta Carinae, violent mass ejections were quite common; chaotic eruptions have marred the system, which usually blasts parts of itself into space. However, the Great Eruption was specifically spectacular. Among the two stars, the larger one is a huge, unstable star reaching the end of its life, and what astronomers observed more than 150 years ago was, actually a near-death experience of the stellar.
Only Sirius—which is nearly one thousand times nearer to Earth—outshines the ensuing rush of light. For a time, this light made Eta Carinae a vital navigation star for sailors in the southern seas. Such a close call almost destroyed Eta Carinae, and the intensity of light slowly diminished. Scientists exploring the star today will still be able to view the Great Eruption’s signature on its surroundings; the massive dumbbell shape is the result of the gas, dust, and other kinds of filaments that were flung into space in the expulsion. Such hot glowing clouds are called the Homunculus Nebula, and since its launch in 1990, have been a target of the Hubble Space Telescope.
As a matter of fact, almost every instrument on the Hubble Space Telescope has imaged the volatile star for more than 25 years. The cosmic drama play out has been observed by astronomers in ever greater resolution. This recent image was produced by using the Wide Field Camera 3 of the Hubble Space Telescope to chart the warm magnesium gas shining in ultraviolet light (indicated in blue color).
Researchers have known for a long time that the outer material flung off in the 1840s eruption was heated by the generated shock waves when it propelled into a material earlier ejected from the star.
The group who successfully took this recent image was hoping to detect light from the magnesium emerging from the intricate array of filaments observed in the light from glowing nitrogen (indicated in red color). Rather, an entirely new luminous magnesium structure was identified in the space between the outer shock-heated nitrogen-rich filaments and the dusty bipolar bubbles.
We've discovered a large amount of warm gas that was ejected in the Great Eruption but hasn't yet collided with the other material surrounding Eta Carinae. Most of the emission is located where we expected to find an empty cavity. This extra material is fast, and it 'ups the ante' in terms of the total energy of an already powerful stellar blast.
Nathan Smith, Department of Astronomy and Steward Observatory, University of Arizona
Smith was also the lead investigator of the Hubble program.
This recently exposed data is significant for inferring the way the eruption started, since it denotes the energetic and rapid ejection of material that could have been ejected by the star soon before the expulsion of the remaining nebula. More observations are required by astronomers to precisely determine when the material was ejected and how rapidly it is moving.
The streaks seen in the blue region beyond the lower-left bubble are another prominent trait of the image. Such streaks appear where the light rays of the star poke via the dust clumps distributed along the surface of the bubble. Wherever it hits the dense dust, the ultraviolet leaves a long thin shadow light that eventually extends further than the lobe into the surrounding gas.
“The pattern of light and shadow is reminiscent of sunbeams that we see in our atmosphere when sunlight streams past the edge of a cloud, though the physical mechanism creating Eta Carinae's light is different,” observed team member Jon Morse of BoldlyGo Institute in New York.
According to the researchers, this method of searching in ultraviolet light for warm gas could be used for studying other kinds of stars and gaseous nebulae.
We had used Hubble for decades to study Eta Carinae in visible and infrared light, and we thought we had a pretty full account of its ejected debris. But this new ultraviolet-light image looks astonishingly different, revealing gas we did not see in either visible-light or infrared images. We're excited by the prospect that this type of ultraviolet magnesium emission may also expose previously hidden gas in other types of objects that eject material, such as protostars or other dying stars; and only Hubble can take these kinds of pictures.
Nathan Smith, Department of Astronomy and Steward Observatory, University of Arizona
The causes of the Great Eruption of the Eta Carinae continue to be a speculative and debatable topic. According to a new theory, Eta Carinae, which once could have weighed 150 Suns, began as a triple system but when the primary star consumed one of its companions, this triggered the mass ejection in the 1840sm ultimately rocketing over 10 times the mass of the Sun into space.
For now, the actual circumstances of that show-stopping burst of light continue to be a puzzle, but astronomers are more confident about the conclusion of this cosmic light show.
The fireworks display of the Eta Carinae is destined to reach its culmination when it bursts as a supernova, significantly exceeding even its last robust outburst. While this might have already occurred, the explosion of light from such a blinding blast would take roughly 7500 years to arrive at Earth.