Astronomers observing the Rosette Nebula, a huge cloud of gas and dust 4600 light years from Earth in the constellation Monoceros (the Unicorn), have found that tiny, round, dark clouds called globulettes have the right characteristics to form free-floating planets with no parent star. New observations, made with Chalmers University of Technology telescopes, show that not all free-floating planets were thrown out of existing planetary systems. They can also be born free. The study shows that the tiny clouds are moving outwards through the Rosette Nebula at high speed, about 80,000 kilometres per hour.
Previous research has shown that there may be as many as 200 billion free-floating planets in our galaxy, the Milky Way. Until now scientists have believed that such “rogue planets”, which don’t orbit around a star, must have been ejected from existing planetary systems. New observations of tiny dark clouds in space point out another possibility: that some free-floating planets formed on their own.
The team collected observations in radio waves with the 20-metre telescope at Onsala Space Observatory in Sweden, in submillimetre waves with APEX in Chile, and in infrared light with the New Technology Telescope (NTT) at ESO’s La Silla Observatory in Chile.
“We found that the globulettes are very dense and compact, and many of them have very dense cores. That tells us that many of them will collapse under their own weight and form free-floating planets. The most massive of them can form so-called brown dwarfs”, says team member Carina Persson, astronomer at Chalmers University of Technology. Brown dwarfs, sometimes called failed stars, are bodies whose mass lies between that of planets and stars.
”We think that these small, round clouds have broken off from tall, dusty pillars of gas which were sculpted by the intense radiation from young stars. They have been accelerated out from the centre of the nebula thanks to pressure from radiation from the hot stars in its centre”, explains Minja Mäkelä, astronomer at the University of Helsinki.
According to Gösta Gahm and his team, the tiny dark clouds are being thrown out of the Rosette Nebula. During the history of the Milky Way, countless millions of nebulae like the Rosette have bloomed and faded away. In all of these, many globulettes would have formed.
“If these tiny, round clouds form planets and brown dwarfs, they must be shot out like bullets into the depths of the Milky Way”, says Gösta Gahm. “There are so many of them that they could be a significant source of the free-floating planets that have been discovered in recent years”, he says.
Astronomers know of almost 900 planets which orbit around other stars than the Sun, but free-floating planets have also been found. Some have been discovered using a technique called microlensing, in which the planet is found when it passes in front of a background star, temporarily making it look brighter. This is an effect predicted by Einstein’s theory of general relativity, in which the light from the star is bent when the planet passes in front of it, a so-called gravitational lens. Scientists have estimated that the number of free-floating planets in our galaxy may exceed 200 billion.
The team observed radio waves from molecules of carbon monoxide using the 20-metre radio telescope at Onsala Space Observatory, Sweden, and submillimetre light with the telescope APEX at 5100 metres altitude in the Atacama desert in northern Chile. APEX is a collaboration between the Max Planck Institute for Radio Astronomy in Bonn, Germany, Onsala Space Observatory and ESO, with operations of the telescope entrusted to ESO. Observations in infrared light were made using the 3.58 metre New Technology Telescope (NTT) at ESO’s La Silla Observatory.
The Daily Galaxy via http://www.chalmers.se/en/news/
Image credit: ESO/M. Mäkelä