Space

Rebel stars spotted forming in the turbulent center of the Milky Way

Rebel stars spotted forming in...
An artist's rendition of a young solar system, where a protostar pulls in material from a parent cloud of dust and gas into a rotating disk (right), and gives off jets of material (left) from its north and south poles
An artist's rendition of a young solar system, where a protostar pulls in material from a parent cloud of dust and gas into a rotating disk (right), and gives off jets of material (left) from its north and south poles
View 3 Images
An ALMA image of the Milky Way's central supermassive black hole (shown at the illustrated star), surrounded by 11 protostars (marked 1 to 11)
1/3
An ALMA image of the Milky Way's central supermassive black hole (shown at the illustrated star), surrounded by 11 protostars (marked 1 to 11)
The double-lobe feature of a young protostar, which the ALMA observatory can detect to identify the object and its age
2/3
The double-lobe feature of a young protostar, which the ALMA observatory can detect to identify the object and its age
An artist's rendition of a young solar system, where a protostar pulls in material from a parent cloud of dust and gas into a rotating disk (right), and gives off jets of material (left) from its north and south poles
3/3
An artist's rendition of a young solar system, where a protostar pulls in material from a parent cloud of dust and gas into a rotating disk (right), and gives off jets of material (left) from its north and south poles

At the center of the Milky Way galaxy there sits a supermassive black hole with the mass of about 4 million Suns. With strong swirling gravitational forces and intense UV light and X-ray radiation, the region around it is one of the most extreme environments in the galaxy. That was thought to be too harsh to harbor star formation, but almost a dozen young, rebellious stars have now been spotted there, triggering a rethink of our understanding of how stars are born.

Normally, stars start life as huge clouds of dust and gas in the disk of a galaxy. Particularly dense sections of these clouds eventually begin to collapse under their own gravity, forming stellar buds known as protostars. In turn, these protostars pull in more dust and gas from the parent cloud and gradually grow into a star.

An ALMA image of the Milky Way's central supermassive black hole (shown at the illustrated star), surrounded by 11 protostars (marked 1 to 11)
An ALMA image of the Milky Way's central supermassive black hole (shown at the illustrated star), surrounded by 11 protostars (marked 1 to 11)

This process is often seen in action in stellar nurseries such as the Orion Nebula, where the conditions are just right. But strong tidal forces can whip the dust away from these budding cores and prevent them from growing properly, while intense radiation can disturb the cloud in the first place.

Flying in the face of that assumption is the recent observation by the Atacama Large Millimeter/submillimeter Array (ALMA) of 11 protostars happily forming in that hostile territory. These low-mass objects, which may one day grow into stars like our Sun, sit just three light-years away from the supermassive black hole at the galactic center.

"Despite all odds, we see the best evidence yet that low-mass stars are forming startlingly close to the supermassive black hole at the center of the Milky Way," says Farhad Yusef-Zadeh, lead author of a new paper describing the discovery. "This is a genuinely surprising result and one that demonstrates just how robust star formation can be, even in the most unlikely of places."

The double-lobe feature of a young protostar, which the ALMA observatory can detect to identify the object and its age
The double-lobe feature of a young protostar, which the ALMA observatory can detect to identify the object and its age

The rebels were spotted thanks to their hourglass-shaped "double lobes", which are created when some of the dust and gas pulled into the protostar is ejected in twin jets from the object's north and south poles. ALMA can pick out these plumes because of molecules like carbon monoxide, which glow brightly at the millimeter wavelengths that the instrument is designed to focus on.

Young stars have been seen forming under similar circumstances before: Earlier this year, the European Southern Observatory noticed young stars forming under similar extreme conditions at the center of a pair of colliding galaxies, but these objects were much bigger and older, at up to 10 million years. These new babies are a mere 6,000 years old, and are closer to the black hole.

The researchers have outlined possible ways the stars might form under these less-than-ideal conditions. To hold the protostars together long enough for them to grow, other forces must be compressing the material. For example, high-velocity gas clouds could be charging through the interstellar medium, or jets given off by the supermassive black hole itself could be squashing the matter into star-forming spots.

"The next step is to take a closer look to confirm that these newly formed stars are orbited by disks of dusty gas," says Mark Wardle, co-investigator on the research. "If so, it's likely that planets will eventually form from this material, as is the case for young stars in the galactic disk."

The research was published in Astrophysical Journal Letters.

Source: National Radio Astronomy Observatory

2 comments
ValeriyPolulyakh
Star formation is one of the least comprehended phenomenon in astrophysics. Is there a general theory of star formation? No, there is not. There is a number of models based on computer simulations which include supersonic hydrodynamics with non-ideal MHD turbulence influenced by gravity. They include the line and continuum radiative processes of the energy transfer; a number of chemical processes with dissociation, recombination and ionization, with uncertain nomenclature of atoms and molecules, unknown magnetic fields and formation and destruction of dust particles. In addition there is macrophysics that is an environment in the molecular clouds, clumps and cores; inclusion in the multiple systems, collisions among stellar systems; jets and outflows; radiation pressure. https://www.academia.edu/14720924/The_Star_Formation https://www.academia.edu/12468184/Are_there_Black_Holes_and_Dark_Matter_in_the_Milky_Way
Gene Preston
If these rogue stars were on an elliptical orbit they could have formed farther away from the center and then swept past the center after the star had formed. I think the barrel shape of the Milky Way is rich in elliptical orbits of stars rather than circular orbits. Am I wrong on this?