Did the Sun Actually Have a "Nemesis?"

Is it part of a binary system now? Highly unlikely.

Did it once have a binary companion?   Almost certainly.

Let's review:

Although the notion of a second Sun dates back centuries, the first scientific paper in reference to the Sun’s twin, nicknamed ”Nemesis,” was published in 1984. Entitled “Periodicities of Extinctions in the Geological Past,” this paper’s two authors, University of Chicago geophysicists David M Raup and John Sepkoski, proposed that mass extinctions during the last 250 million years exhibited a 26-million year periodicity. They further noted that two of these events

• Cretaceous–Paleogene 66 million years ago
• Eocene–Oligocene 33.9 - 33.4 million years ago

were both directly attributable to asteroid impacts. As these two researchers could not ascribe this periodicity to any terrestrial phenomenon, they cited the possibility of a celestial cause: either stellar or galactic. While this cause might include galactic motions,* another hypothesis involved the presence of a binary companion to the Sun: a red or even brown dwarf with a mean distance of 1.5 light years from the Sun. With a presumed orbital period of 26 - 27 million years, this star could induce perturbations on the Oort Cloud cometary nuclei when it passed close to periastron, the point of least separation distance between two stars. The resultant onslaught would likely send a few comets hurtling toward Earth. The resultant impacts, if sufficiently energetic, could cause an extinction event.

The “Nemesis” theory proposed that a binary companion to the Sun, either a red or brown dwarf, could push many Oort Cloud cometary nuclei in toward the inner solar system whenever it reached periastron. Any such comet, if it struck Earth, could cause a mass extinction event. The Oort Cloud is a spherical distribution of cometary nuclei that could extend between 2,000 - 200,000 AU from the Sun. (AU = astronomical unit. equal to Earth’s mean distance from the Sun.) Image credit: Laurine Moreau

Or, so the theory went.

However, three notable surveys, the Infrared Astronomical Satellite (IRAS) in the 1980s 2MASS (The Two-Micron All Sky Survey) between 1997–2001 and the Wide-Field Infrared Survey (launched Feb 2009) failed to detect any star at the proposed distance of “Nemesis.” Considering that Nemesis was believed to be a red or brown dwarf (any star more luminous would have been readily visible to the unaided eye), these three comprehensive surveys should have detected any such binary companion. The peak emissions of such stars is within the infrared spectrum. Also, as of now, approximately 1,800 brown dwarfs have been discovered. If Nemesis had been a brown dwarf, it would have been the closest one to us and should have already been found.

It seems highly unlikely that the Sun is now part of a binary system.

However, it does seem likely that the Sun did have such a companion quite a while ago.

In 2018, Harvard scientists Dr. Avi Loeb, Frank B. Baird Jr. and Amir Siraj, published a study in “The Astrophysical Journal Letters,” stating that the Sun may have once had a binary companion of comparable size and mass. They based this theory on the density and distribution of material within the Oort Cloud. We know that the Sun, like almost all stars- formed in a cluster. The stars gathered extraneous material within the cluster around themselves during and immediately after formation. Considering the sheer amount of material within the Oort Cloud, the Sun must have had a binary companion during its infancy to produce the gravitational attraction necessary to gather together this matter.

A solar “twin? “ This artistic depiction features the Sun and its proposed binary companion during its infancy. According to researchers at the Harvard-Smithsonian Center for Astrophysics, such a star would have helped the Sun to capture much of the material now contained within the Oort Cloud. Image credit: Universe today.

The gravitational influence of passing stars may have ultimately wrested this companion away from the Sun, hence its current absence. This detachment could have occurred as many as four billion years ago.

Also, radio observations of a giant molecular cloud in the Perseus region have shown that most if not all stars form as pairs. Statistical modeling of this cloud demonstrated that the observed distribution of stars could only be explained if all the stars at least initially formed as “wide binaries,” defined as binaries with a mean separation distance of more than 500 AU. Steven Stahler, A UC Berkeley astronomer and a co-author of the study related to the observations, was quoted as having said, “We are saying, yes, there probably was a Nemesis, a long time ago.”

So, yes, it seems highly likely that Earth had two suns a long time ago…perhaps so long ago that by the time Earth cooled and life started to develop, Nemesis had moved on.

A radio image of a forming triple star system within a giant molecular cloud in Perseus. Image credit: Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. Credit: Bill Saxton, ALMA (ESO/NAOJ/NRAO), NRAO/AUI/NSF

*The Shiva Hypothesis, named for the Hindu god of destruction and developed by William Napier and Victor Clube (1979), asserts that these periodic extinctions are solar system motions through the Milky Way Galaxy, itself. For instance, a 2008 study at the Cardiff Centre for Astrobiology suggests that the solar system passes through the galactic plane every 35 - 40 million years. The passage through this comparatively high density region could perturb myriad Oort Cloud cometary nuclei. The Sun’s gravity could then draw them into the inner solar system, where some would strike Earth, precipitating a mass extinction event.