Eta Carinae Possibly Deciphered

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. Credits: NASA, ESA, and the Hubble SM4 ERO Team
Print Friendly, PDF & Email

By Kevin Roeten:

Kevin Roeten
Science Editor

Evidently, Eta Carinae is a star ready to explode. When – next year, or maybe one million years from now. Eta Carinae‘s mass is 100 times greater than our Sun, which makes it a likelihood for a full-blown supernova. Historical records show 150 years ago Eta Carinae became one of the brightest stars in the southern skyEta Carinae, in the Keyhole Nebula, is the only star currently emitting natural LASER light.

This image taken in 1996, brought out new details in the unusual nebula surrounding this rogue star. Now, two distinct lobes, a hot central region, and many radial streaks are readily visible. The lobes are filled with lanes of gas and dust which absorb the blue and ultraviolet light emitted. There is no specific reason for the streaks, but they are obvious.

Eta Carinea has been determined to have a temperature of 37,200 Kelvin, and an age of approximately 3 million years. The two main stars of the Eta Carinae system have an eccentric orbit with a period of 5.54 years. The primary is a peculiar star similar to a luminous blue variable[LBV] initially 150–250 [MSolar Mass] of which it has lost 30 M already, and is expected to explode as a supernova in the astronomically near future. This is the only star known to produce ultraviolet laser emission. The secondary star, is around 30–80 times as massive as the Sun. The system is heavily obscured by the Homunculus Nebula, material ejected from the Great Eruption.

Edward Halley gave an apparent magnitude of “4” at the time of discovery, which has been calculated as magnitude 3.3 on the modern scale. The handful of possible earlier sightings suggest Eta Carinae was not significantly brighter than this for much of the 17th century. It is unknown whether Eta Carinae varied significantly in brightness over the next 50 years.

A new brightening started in 1887, and peaked at about magnitude 6.2 in 1892, then at the end of 1895 faded rapidly to about magnitude 7.5. Although there are only visual records of the 1890 eruption, it has been calculated that Eta Carinae was suffering 4.3 magnitudes of visual extinction due to the gas and dust ejected in the Great Eruption. An unobscured brightness would have been magnitude 1.5–1.

Eta Carinae [η Carinae] is a stellar system containing two stars with a combined luminosity greater than five million times the Sun. The peaks in 1827, 1838, and 1843 are likely to have occurred at the periastron passage. This the point the two stars are closest together in this binaryorbit.[8]  Eta Carinae is located around 7,500 light-years distant in the constellation Carina. Which means we will never see the constellation unless it has gone supernova 7,500 years ago.

Previously a 4th-magnitude star, it brightened in 1837 and became brighter than Rigel at the start of the Great Eruption. Eta Carinae became the second-brightest star in 1843 before fading well below naked eye visibility after 1856. In a smaller eruption, it reached 6th magnitude in 1892 before fading again. It has brightened consistently since about 1940, becoming brighter than magnitude 4.5 by 2014.

The two stars of the Eta Carinae system have an eccentric orbit with a period of 5.54 years.  The primary is a peculiar star similar to aluminous blue variable [LBV] that was initially 150–250 M of which it has lost at least 30 M already, and is expected to explode as asupernova in the astronomically near future. This is the only star known to produce ultraviolet laser emission. The secondary star is 80 times as massive as the Sun. The system is heavily obscured by the Homunculus Nebula— which is a is a bipolar emission and reflection nebulasurrounding the massive star system Eta Carinae, about 7,500 light-years (2,300 parsecs) from Earth. The nebula is embedded within the much larger Carina Nebula, and contains material ejected during the Great Eruption.

Edward Halley, of Halley’s comet, gave an apparent magnitude of “4” at the time of Eta Carinae discovery, which is calculated as magnitude 3.3 the entire energy output of the system to be observed at wavelengths not strongly affected by interstellar extinction. Far infrared observations show a large mass of dust at 100–150 K, suggesting a total mass for the Homunculus of 20 solar masses [M] or more. This is much larger than previous estimates, and is all thought to have been ejected in a few years during the Great Eruption.[7]  Near-infraredobservations can penetrate the dust at the modern scale.

One theory of Eta Carinae’s ultimate fate is collapsing to form a black hole—energy released as jets along the axis of rotation forms gamma-ray bursts. Drawing of a massive star collapsing to form a black hole. Energy released as jets along the axis of rotation forms a gamma ray burst that lasts from a few milliseconds to minutes. Such an event within several thousand light years of Earth could disrupt the biosphere by wiping out half of the ozone layer, creating nitrogen dioxide and potentially cause a mass extinction.

Emissions are very characteristic of novae, where ejected material initially radiates like a pseudo-photosphere. The vast majority of the electromagnetic radiation from the central stars is absorbed by surrounding dust. This allows almost high resolution to observe features completely obscured at visual wavelengths The central region of the Homunculus contains a smaller Little Homunculus from the 1890 eruption.

Direct spectral observations did not begin until after the Great Eruption, but light echoes from the eruption reflected from other parts of the Carina Nebula were detected using the U.S. National Optical Astronomy Observatory’s Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory.

Annotated image of Carina Nebula

The dusty, bipolar cosmic cloud is around 1 light-year across The full scale Homunculus surrounds Eta Carinae, famously unstable massive stars in a binary system embedded in the extensive Carina Nebula about 7,500 light-years distant from earth. Between 1838-1845, Eta Carinae underwent the Great Eruption becoming the second brightest star in Earth’s sky and ejecting the Homunculus Nebula. Eta Carinae itself still undergoes violent outbursts, a candidate to explode in a spectacular supernova in the next million years.

The 5.5 year orbital cycle produces strong spectral changes at periastron known as spectroscopic events. Certain wavelengths of radiation suffer eclipses, either due to actual occultation by one of the stars. Despite being a result of orbital rotation, these events vary significantly during cycles to cycle. These changes have become stronger since 2003, and it is generally believed long-term changes in the stellar winds or previously ejected material may be the culmination of a return to the of the star before its Great Eruption.

The two stars are so massive and bright, the radiation they produce rips off their surfaces and spews them into space. This expulsion of stellar material is referred to as stellar “wind”, possibly travelling at millions of kph. Measurements were done through the Doppler effect. Astronomers use the Doppler effect shifts to calculate how fast stars and other astronomical objects move toward, or away from Earth. The movement of an object towards or away from us causes a slight shift in its spectral lines. The velocity of the motion is calculated from this shift.

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.
Credits: NASA, ESA, and the Hubble SM4 ERO Team

The nebula was spotted 7500 light-years away from earth about 15 years ago, but astronomers theorize the end of earth could be a possibility in that many years. Nonetheless, the author doesn’t plan to be around this neck of the woods…

******

Kevin Roeten can be reached at roetenks@CHARTER.NET.

© Copyright by Kevin Roeten, 2018. All rights reserved.

Kevin Roeten
About Kevin Roeten 168 Articles
CHO's science editor Kevin Roeten is a former Chemical Engineer. He enjoys riding the third rail of journalism: politics and religion. As an orthodox Catholic, Roeten appreciates the juxtaposition of the two supposedly incompatible subjects.   Kevin is a Guest Columnist for the Asheville Citizen-Times, and the Independent (Ohio), and writes for numerous blogs (Nolan Chart, Allvoices) and newspapers, including USA Today.   A collaborator in the book Americans on Politics, Policy, and Pop Culture (Jason Wright and Aaron Lee), he is also an amateur astronomer, and delves into scientific topics.   Kevin Roeten can be reached at roetenks@charter.net.