An article published in “The Astrophysical Journal Letters” describes a research that led to the discovery of stars really out of the ordinary. Those are binary systems consisting of two very massive stars where immense eruptions can take place. These systems are twins of Eta Carinae, which became famous for the eruption sighted in the 19th century. Examining observations made using the Hubble and Spitzer space telescopes a group of researchers found 5 candidates in other galaxies.
The Eta Carinae binary system is about 7,500 light years away from Earth and is composed of two very massive stars as the larger one is a blue hypergiant that has a mass about 90 times the Sun’s and the other has a mass that could be even more than 30 times the Sun’s. Their overall brightness is millions of times the Sun’s.
The Eta Carinae system became famous in the 19th century: in 1820 its brightness started increasing reaching a peak in 1843, an event that was called the Great Eruption and made it appear for a few decades as the second brightest star in the sky. Subsequently, its brightness fell considerably then rose again briefly on a couple of occasions during the 20th century.
The instruments of the 19th century were far from the ones we have today and astronomers haven’t found an explanation for an eruption such as Eta Carinae’s yet. Around its stars there are traces of an explosion that formed the Homunculus Nebula, a structure so far considered unique.
To get some answers and better understand the evolution of massive stars like those that form that binary system, a group of researchers tried to look for other similar systems. To succeed, it was necessary to develop the equivalent of Eta Carinae’s fingerprints in the visible light and infrared.
The research started in 2012 examining seven galaxies for about two years. A class of stars less massive and less luminous than Eta Carinae that are interesting from the scientific point of view for other reasons was found but those aren’t its twin. For this reason, in 2015 the research was extended to other galaxies and finally came the expected results.
In the galaxy M83, 15 million light years from Earth, two candidates were found and three more were found respectively in the NGC 6946, M51 and M101 galaxies, between 18 and 26 million light years away from Earth. These candidates showed characteristics at visible light and infrared similar to Eta Carinae. This means that most likely they contain a high mass star buried in a mass of gas and dust between 5 and 10 solar masses.
Additional observations are needed to confirm that the five candidates really are Eta Carinae’s twins. They will be among the research targets of the James Webb Space Telescope, whose launch is now scheduled for 2018. It’s equipped with the Mid-Infrared Instrument (MIRI) instrument, ideal for observations at infrared the frequencies Eta Carinae especially shines at.