Tiny, round, cold clouds in
space have all the right characteristics to form 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.
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.
A team of astronomers from Sweden and Finland used several
telescopes to observe the Rosette Nebula, a huge cloud of gas and dust
4600 light years from Earth in the constellation Monoceros (the
Unicorn).
They 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.
”The Rosette Nebula is home to more than a hundred of these tiny
clouds – we call them globulettes”, says Gösta Gahm, astronomer at
Stockholm University, who led the project.
“They are very small, each with diameter less than 50 times the
distance between the Sun and Neptune. Previously we were able to
estimate that most of them are of planetary mass, less than 13 times
Jupiter’s mass. Now we have much more reliable measures of mass and
density for a large number of these objects, and we have also precisely
measured how fast they are moving relative to their environment”, he
says.
“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.
The study shows that the tiny clouds are moving outwards through
the Rosette Nebula at high speed, about 80 000 kilometres per hour.
”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.
More about exoplanets and free-floating planets
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.
More about the research
The study has been published in the article Mass and motion of globulettes in the Rosette Nebula in the July issue of the journal Astronomy & Astrophysics.
The team consists of Gösta Gahm (Stockholm University, Sweden), Carina
M. Persson (Onsala Space Observatory at Chalmers University of
Technology, Sweden), Minja M. Mäkelä (Department of Physics, University
of Helsinki, Finland) and Lauri K. Haikala (Finnish Centre for Astronomy
with ESO [FINCA], University of Turku, Finland).
More about the telescopes
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.
More about Onsala Space Observatory
Onsala Space Observatory is Sweden's national facility for radio
astronomy. The observatory provides researchers with equipment for the
study of the earth and the rest of the universe. In Onsala, 45 km south
of Gothenburg, it operates two radio telescopes and a station in the
international telescope Lofar. It also participates in several
international projects. The observatory is hosted by Department of Earth
and Space Sciences at Chalmers University of Technology, and is
operated on behalf of the Swedish Research Council.
For more information, please contact:
Robert Cumming,
astronomer and communications officer,
Onsala Space
Observatory at Chalmers University of Technology,
+46 31-772 55 00 or
+46-70-493 31 14,
email: robert.cumming@chalmers.se
Gösta Gahm, astronomer,
Stockholm University,
+46-73-785 70 71,
email: gahm@astro.su.se
Carina Persson,
astronomer,
Onsala Space Observatory at Chalmers University of Technology,
+46 31-772 55 37,
email: carina.persson@chalmers.se
Minja Mäkelä,
Department of Physics,
University of Helsinki,
+358-9-191 50811,
email: minja.makela@helsinki.fi
