Sun May Blast Two Jets of Plasma into Interstellar Space

As the sun travels through the galaxy, its extended magnetic bubble (known as the heliosphere), interacts with the gases and magnetism in the space between the stars — a vast region known as the interstellar medium.

However, astronomers have assumed that the heliosphere gets dragged out into a comet-like tail (not too dissimilar to a stretched-out raindrop), shaped by the interstellar medium, but scientists now think the sun’s magnetic field strength has been underestimated, overturning our understanding as to how our solar system looks from afar.

The heliosphere reaches far beyond the orbit of Pluto and it is filled with the energetic particles ejected by the sun contained within the solar wind. The sun’s magnetic field pushes outward with the solar wind, creating a magnetic bubble separating solar plasma from the interstellar medium. A balance of pressure between the outward pressure of the solar wind and the inward pressure of the interstellar medium is reached at the heliosphere’s boundary, called the heliopause.

As the sun is moving, it was assumed that the heliopause is being shaped through its interaction with the interstellar magnetic field, but new models and observations suggest that the sun’s magnetic field is actually dominating its shape. Rather than producing a ‘classical’ comet-like tail researchers now suggest two tails are formed from jets protruding from the sun’s north and south poles.

“Everyone’s assumption has been that the shape of the heliosphere was molded by the flow of interstellar material passing around it,” said astronomer Merav Opher, of Boston University, lead author of a paper published in the Astrophysical Journal Letters in February. “Scientists thought the solar wind flowing down the tail could easily pull the magnetic fields in the heliosphere along as it flowed by, creating this long tail. But it turns out the magnetic fields are strong enough to resist that pull — so instead they squeeze the solar wind and create these two jets.”

Interestingly, other stars in our galaxy have been observed with this two-jet heliosphere morphology, but now the mechanisms behind the two tails are being revealed inside our own solar system. For example, the star BZ Cam, below, exhibits a shortened heliosphere shaped by 2 jets:

The revelation that our basic comet-like model of the sun’s heliosphere was incomplete came when NASA’s Voyager 1 probe exited the heliosphere. On measuring the direction of the interstellar magnetic field — the first mission ever to do so — astronomers were surprised to find it matched the direction of our sun’s magnetic field, contrary to predictions.

By adding these findings to high-resolution computer simulations of the sun’s magnetic field, it became apparent that these jets had a strong influence over the heliosphere’s interstellar shape.

“If there were no interstellar flow, then the magnetic fields around the sun would shape the solar wind into two jets pointing straight north and south,” said co-author Jim Drake at the University of Maryland in College Park. “The magnetic fields contract around these jets, shooting the solar wind out like squishing a tube of toothpaste.”

Read more at Discovery News