Eta Carinae is Getting Brighter Because a Dust Cloud was Blocking our View

In addition to being one of the most beautiful and frequently photographed objects in the night sky, Eta Carinae also has also had the honor of being one of the sky’s most luminous stars for over a century and a half. In addition, it has been a scientific curiosity since its giant ejected nebula (Homunculus) contains information about its parent star.

It is therefore sad news that within a decade or so, we will no longer be able to see the Homunculus nebula clearly. That was the conclusion reached in a new study by an international team of researchers. According to their findings, the nebula will be obscured by the growing brightness of Eta Carinae itself, which will be ten times brighter by about 2036.

Astronomers became aware of Eta Carinae in 1847, when the giant eruption that ejected its nebula also made it the second-brightest star in the sky after Sirius. At the time, the star was visible even in broad daylight, which made it easily distinguishable from other, similarly unstable stars called Luminous Blue Variables (LBVs) whose nebulae are not so clearly visible.

The new study, which recently appeared in the Monthly Notices of the Royal Astronomical Society (MNRAS), was led by Augusto Damineli of the University of Sao Paulo’s Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG) and included researchers from the NASA Goddard Space Flight Center, the Max Planck Institute for Radio Astronomy, and multiple institutes and universities.

According to their study, Eta Carinae’s brightness is likely caused by the dissipation of a dust cloud positioned in front of it (as seen from Earth). This contradicts previously-held notions that the brightness is intrinsic to the star itself. In fact, they claim that this cloud is responsible for shrouding the star and its winds, which obscures much of the light coming from it towards Earth.

The surrounding Homunculus is not affected by this cloud, however, since it is over 200 times larger. But by 2032 (plus or minus four years), the dusty cloud will have dissipated and the brightness of the central star will begin to obscure the Homunculus nebula. In other words, Eta Carinae will appear brighter and the nebula itself will no longer be visible.

While this certainly sounds like bad news, the team emphasizes that there is an upside to this. For one, the increased visibility of the star will allow for deeper study of Eta Carinae itself, which will settle some long-standing questions. For instance, astronomers have puzzled over whether Eta Carinae is in fact one star or a binary system.

As Anthony Moffat, a professor of astrophysics at the University of Montreal and a co-author on the study, explained in a UdeM press release:

“There have been a number of recent revelations about this unique object in the sky, but this is among the most important. It may finally allow us to probe the true nature of the central engine and show that it is a close binary system of two very massive interacting stars.”

“There have been a number of recent revelations about this unique object in the sky, but this is among the most important. It may finally allow us to probe the true nature of the central engine and show that it is a close binary system of two very massive interacting stars.”

To paraphrase Heraclitus, “The only constant is change”. In a Universe where everything is in flux, change can provide new and exciting opportunities for research. And with next-generation telescopes coming online soon, Eta Carinae could prove to be a very interesting subject of study.

Further Reading: University of Montreal