Binary Star Systems: Can They Teach Us How Planets Form?

New research has shed light on how planets form around paired stars. Looking into these systems might change what we know about how planets form around different stars.

The Dynamics of How Planets Form in Binary Systems

Over half of all stars have a companion star. In our solar system, on the other hand, planets circle a single star. Planets in these pairs can also be in "circumstellar orbit" or "circumbinary orbit."

Astronomers used ALMA and the Keck II 10-meter telescope to study two systems of two stars. This finding could help us understand how binary systems can help or hurt worlds.

Like how a single star forms, thick clouds of gas between stars create too-dense areas that fall apart under their weight to create a "protostar." The protostars use the gas and dust in their bodies to fuel nuclear fusion, which turns them into main-sequence stars. Big clouds between the stars can make two or three stars.

These clouds leave behind "protoplanetary disks," which could be around stars or binaries. Scientists are trying to determine why these disks stay together long enough to form planets and break apart.

Studying these issues in circumstellar rings in pre-main-sequence protostar binary systems might be possible. The shapes, sizes, and directions of early disks can show how complex interactions affect the conditions for planet formation.

D.F. Tau is a binary system with two protostars about 0.6 times the sun's mass. It is 150 light-years from Earth and is in the star-forming area of Taurus. It takes 44 Earth years for their extended circles to finish, and D.F. Tau stars are 14 times farther from each other than the sun.

ALMA discovered that the cloud between the stars that gave birth to these stars split into two rings that circle the stars. One gives matter to the core star D.F. Tau A, and the other has split off from D.F. Tau B.

As the new star spins quickly, the disk's center looks worse for wear. Young stars may rotate, disks may be magnetically locked to them, and disks may break apart early on. If D.F. Tau's orbit, circumstellar disks, and star inclinations are not lined up correctly, it could change how disks evolve.

Possible Planet Formation

The second system, F.O. Tau, is only 2.8 million years old and is 450 light-years away. There is 22 times more space between its stars, F.O. Tau A and B, than between Earth and the sun.

ALMA found that F.O. Tau's disks aligned with this binary star's path. Both stars spin very slowly, and their rings around the stars are magnetically connected to their protostars. This suggests that slower stars with circle orbits, like F.O. Tau, might be better for making planets than stars with longer orbits that move faster.

ALMA has found spiral patterns, holes, and ring shapes in several single and double-star disks. These structures can't be seen for D.F. Tau and F.O. Tau, but studying their large-scale features has helped us learn more about how planets grow.

At the 244th AAS meeting, the experts discussed their results and stressed the importance of studying binary star systems to understand how planets form.

What is the ALMA?

The Atacama Large Millimeter/Submillimeter Array (ALMA), built in northern Chile by people from North America, East Asia, and Europe, is the world's most advanced telescope for astronomy. It takes pictures of how planets form, the Milky Way, and the very first galaxies and stars.

ALMA, a transformational radio telescope, studies radio-infrared cosmic light. Most things in space give off this energy, which is why astronomers need it. ALMA's 66 high-precision dish antennas pick up tiny space signals in the dry, high-altitude Atacama Desert. This gives us new information about how the universe began and is changing now.

Lastly, ALMA and Keck II can show how planets form by looking at systems with two stars. Figuring out the factors that help or hurt planet formation in these systems helps us understand how planets are born and how they change over time. It also shows us how complicated and changing our universe is.