When two hot stars brushed by: Ancient stellar flyby left its mark near our Solar System

Cosmic Drive-By: Two Blazing Stars Once Skimmed Our Sun and Changed Local Space (Image: Canva)

A quiet trace in nearby space has stirred curiosity. New research suggests two huge stars once passed close to our sun, leaving subtle marks inside the clouds surrounding our solar system.

Why did two stars pass so near the sun?

A team led by Michael Shull at the University of Colorado Boulder explored this question in a study published on 24 Nov. in The Astrophysical Journal. Their work pieces together how Earth’s local space environment took shape over millions of years.

Earth sits inside a set of local interstellar clouds, thin regions of gas and dust stretching 30 light-years, or 175 trillion miles. Outside those clouds lies the local hot bubble, an area with little gas but intense past activity.

Shull said the clouds may shield Earth from harsh radiation. He noted this protection may have influenced life’s early development.

How did the stars affect the nearby clouds?

The team focused on Epsilon and Beta Canis Majoris. These B-stars sit today in the constellation Canis Major, forming the front and back legs of the Great Dog.

Models show both stars swept past the sun 4.4 million years ago, reaching a distance of 30 to 35 light-years. That is considered very close in cosmic terms.

Their ultraviolet radiation ionised atoms in the surrounding clouds. This stripped electrons from hydrogen and helium, leaving atoms with a positive charge. Scientists can still detect that ionisation today.

Shull said these stars would have shone four to six times brighter than Sirius, now the brightest star in the sky.

What mystery were researchers trying to solve?

For decades, astronomers have detected an unusual mix of ionised gas in the local clouds. Roughly 20% of hydrogen and 40% of helium appear ionised. The helium readings seemed especially high.

The team built models to track the sun’s movement through space at 58,000 miles per hour. They mapped shifting stars and drifting clouds. Shull described this challenge as a “moving jigsaw puzzle”.

Their results point to at least six sources of ionisation. These include three white dwarf stars and radiation from the local hot bubble. That bubble likely formed after 10 to 20 supernovae, which heated gas and filled the region with ultraviolet and X-ray radiation.

Epsilon and Beta Canis Majoris matched the bubble’s influence, adding significant radiation of their own.

What happens next to these stars and the clouds?

Epsilon and Beta Canis Majoris are 13 times the mass of the sun. They burn at 38,000 and 45,000 degrees Fahrenheit, far hotter than the sun’s 10,000 degrees Fahrenheit.

They will burn out within a few million years and eventually go supernova. Shull said these explosions will not threaten Earth but will create an extremely bright display if anyone is around to witness it.

As for the local clouds, the ionisation will fade over time. Positively charged atoms will capture free electrons again, returning to a neutral state over millions of years.

Shull said the team’s work helps explain how Earth’s cosmic surroundings formed and how they may have shaped life’s long history.