Eta Carinae is the biggest and brightest stellar system within 10,000 light-years in our galaxy. In the mid-19th century, a massive explosion took place within Eta Carinae, which launched a huge mass into space, approximately 10 times the sun's mass.

The explosion resulted in a "veil-like" shroud of dust and gas, which makes Eta Carinae a one-of-a-kind object in the galaxy. A recent analysis of NASA's archival data from the Hubble and Spitzer telescopes revealed Eta Carinae isn't so unique after all. The U.S. space agency found five other stellar objects in other galaxies with the same properties.

"The most massive stars are always rare, but they have tremendous impact on the chemical and physical evolution of their host galaxy," explained lead scientist Rubab Khan, NASA's Goddard Space Flight Center postdoctoral researcher. These enormous stars create and dispense high amounts of chemical elements that are crucial to their life. Eventually, the massive stars erupt as supernovas.

The Massive And Luminous Eta Carinae

Eta Carinae can be found 7,500 light-years away from the Carina constellation. It is so bright that it outshines our galaxy's sun by approximately 5 million times.

Its binary system is made up of two enormous stars. The bigger one is roughly 90 times bigger than the sun's mass and the smaller one is a little beyond 30 solar masses.

Eta Carinae is the nearest stellar site for scientists to study high-mass stars, the eruptions and how they are related to the development of massive stars. It is very difficult to catch unique stars after a major eruption, which is often short-lived.

Following the stellar system's great eruption in the 1840s, researchers needed more examples of the same stellar objects to understand the occurrence. Prior to Khan's research, nothing has ever matched Eta Carinae's descriptions.

A massive star ejects gas where dust forms. The dust lowers the star's visible and ultraviolet light by absorbing the light and reradiating it as heat. The reradiated energy comes in the form of longer, mid-infrared wavelengths.

Using the Spitzer data, the team saw a steady brightness increase in the stellar system beginning at about three microns. The brightness peaked between eight and 24 microns. They then compared the light peaking to the dimming in Hubble's data images of other stellar objects. The team was able to analyze the amount of dust present in other stellar objects and compare it to Eta Carinae's data.

Finding The Eta Twins

Khan worked with co-researchers from Ohio State University and George Sonneborn at Goddard to create what seems to be an infrared and optical fingerprint to help recognize potential twins for Eta Carinae. The team called these "Eta Twins."

From 2012 to 2014, the team surveyed seven galaxies but failed in finding Eta Twins. In 2015, the team conducted a follow-up stellar investigation and found two possible candidates in the M83 galaxy which lights 15 million light-years from Earth. The team found three more, one in each of the following galaxies: M101, M51 and NGC 6946. These three galaxies can be found 18 to 26 million light-years from Earth.

The five Eta Twins have the same infrared and optical properties. This means each of them is most likely concealing a massive star within the shroud of dust and gas. The discovery of the five Eta Twins was published in The Astrophysical Journal Letters in December 2015.

NASA's James Webb Space Telescope is scheduled to launch in the latter part of 2018. The new telescope will help in further studying the stars using its Mid-Infrared Instrument (MIRI).

An extensive study will allow scientists to determine each of their physical properties more precisely and confirm if these five Eta Twins are truly similar to Eta Carinae.

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