Hubble discovers mystery object orbiting brown dwarf

Posted by Staff writer

Astronomers have discovered a planet-like object circling a brown dwarf that appears to have formed much more quickly than was previously thought possible.

At five to ten times the mass of Jupiter, it's the right size for a planet. But with the brown dwarf only a million years old, the object hasn't had the time to appear thast most theories say is necessary.

Researchers used the Hubble Space Telescope and Gemini Observatory to directly image the object.

It orbits the nearby brown dwarf at a separation of approximately 2.25 billion miles. But is it really a planet? The answer, says the team, depends on how it was formed.

There are three possibilities. First, that dust in a circumstellar disk slowly agglomerated to form a rocky planet, which then accumulated a large gaseous envelope; second, that a lump of gas in the disk quickly collapsed to form the object; and, third, that it formed directly from the collapse of the vast cloud of gas and dust in the same manner as a star.

If the last scenario is correct, it means that planetary-mass bodies can be made through the same mechanism that builds stars. And it seems the likely solution, as the companion is too young to have formed by the first scenario, which is very slow.

The second mechanism occurs rapidly, but the disk around the central brown dwarf simply didn't contain enough material to make an object that big.

"The most interesting implication of this result is that it shows that the process that makes binary stars extends all the way down to planetary masses. So it appears that nature is able to make planetary-mass companions through two very different mechanisms," says team member Kevin Luhman of the Center for Exoplanets and Habitable Worlds at Penn State University.

The research will appear in the Astrophysical Journal.