Planetary ‘spitballs’ hurtled from galaxy’s centre

Researchers believe a giant black hole at the centre of the Milky Way is hurling planet-sized objects throughout the galaxy, after new research by researchers in the US.

The black hole rips stars apart, sending a long stream of gas whipping outward. The gas gathers itself into these objects before being flung, according to astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA), like ‘spitballs’.

James Guillochon, co-author of the study and from the CfA, said: “Other galaxies like Andromeda are shooting these 'spitballs' at us all the time.”

Calculations suggest the closest of these planet-mass objects may be within a few hundred light years of Earth. With weights estimated between Neptune and several Jupiters, they would glow from the heat of its formation, but not brightly enough to be detected by previous surveys. Future telescopes such as the Large Synoptic Survey Telescope and James Webb Space Telescope may be able to spot these planet-sized objects.

Eden Girma, an undergraduate student at Harvard University involved in the research, said: “A single shredded star can form hundreds of these planet-mass objects. We wondered: Where do they end up? How close do they come to us?“

The large majority of these objects leave the galaxy due to travelling at speeds of about 20 million miles per hour. As most other galaxies have black holes at their centre, it’s likely this is happening elsewhere. James Guillochon from the Harvard-Smithsonian Centre for Astrophysics, said: “Other galaxies like Andromeda are shooting these 'spitballs' at us all the time.”

Girma said to Laboratory News: “We simulated the spatial evolution of these fragments motion with a computer code consisting of two parts: the first modelling a randomly drawn tidal disruption from which we interpolated the number of fragments produced. The second, an integrator, solved the subsequent position, velocity, and acceleration of each fragment.”

Due to a process called tidal disruption, it takes a day for the black hole to rip the star apart and about a year for the fragments to pull themselves back together. Usually planetary formation takes millions of years. After the planet-sized object is launched it would take about a million years for one of these objects to reach Earth’s neighbourhood.

These findings were presented at the American Astronomical Society.